SUGARS

          Sugar is used extensively in cookery, in the preparation of processed fruit products, flavoured syrups, non-alcoholic beverages, confectionery etc. In addition to pure sugar, crude sugar(brown sugar and jaggery), corn syrup and honey are also used.

Types of sugar

Type Characteristics UsesCastor Fine white crystals Bakery Granulated Crystals of medium size General sweetening

agent Cube Crystals compressed to cubes Tea service Icing Fine white powder with or without

starch Cake icings

Golden syrup

Processed to a yellow syrup Cooking and baking confectionery

Molasses Dark – by – product of sugar Cooking and confectionery

Diamond sugar

Small rectangular crystals Used with beetle nuts, confectionery

 Rock sugar

Big slabs Used on festive occasions

Brown sugar

Contain molasses, glucose and fructose pleasing and distinctive flavour

Baked products

Sugar powder

Pulverized granulated sugar Dough nuts, hard puris

Sugar and sugar related products

Pure sugar 

Pure sugar is commonly manufactured from sugar cane or beet root. It contains 99.8% sucrose.

Brown sugar

          Brown sugar is manufactured from sugar cane. It contains about 92% sucrose and 3.7% of invert sugar.

Jaggery   

          Jaggery is mainly obtained from sugar cane though it can also be prepared from palm, date palm and coconut. Jaggery obtained from sugar cane juice contains about 90.0% sucrose and 5.2% invert sugar. It is used in the preparation of peanut candy, puffed rice balls, chick pea candies etc. in India. Jaggery is preferred to sugar because it is rich in iron, gives colour has a typical flavour, gives body or thickness and it is less expensive.

Corn syrup          

          Corn syrup (liquid glucose) is prepared by the hydrolysis of corn starch. It is extensively used in the preparation of confectionery products.

Honey 

          Honey contains about 17% water and 82.5% carbohydrate with small amounts of minerals and vitamins and enzymes. The carbohydrate portion of honey includes invert sugar (glucose and fructose), maltose and sucrose.

Properties

1. Solubility

          In the natural state of foods, sugars are in solution. Crystallization of sugar occurs from a sufficiently concentrated sugar solution, and use of this is made in the commercial production of sugar from  sugarcane and beets. The most soluble sugar is fructose, followed by sucrose and lactose. The sugar that is the most difficult to crystallise than that the least soluble sugar, lactose.

2. Absorption of moisture

          Sugars are hygroscopic. Fructose is more hygroscopic than the other sugars. Cakes made with honey, molasses remain moist for a long time.

3. Fermentation

          Most sugars, except lactose may be fermented by yeasts to produce CO2 gas and alcohol. This is an important reaction in making bread and other baked products. The CO2 leavens the product and the alcohol volatilizes during baking.

4. Acid hydrolysis

          Sucrose is easily hydrolysed by acid but maltose and lactose are slowly acted on. The end products of sucrose hydrolysis are a mixture of glucose and fructose. This mixture is commonly called invert sugar. The monosaccharides are not appreciably affected by acids. Heat accelerates the action of acid.

5. Enzyme hydrolysis

          The enzyme sucrose also called invertase is used in the candy industry to hydrolyze some of the sucrose in cream fondant to fructose and glucose. This is done to produce soft, semi fluid centres in chocolates. The enzyme is commonly added to the fondant layer around the fruit in chocolate coated cherries.

6. Melting point and decomposition by heat

    Caramelization:  With the application of sufficient dry heat, sugar melts or changes to a liquid state. Heating beyond the melting point brings about a number of decomposition changes. As sucrose melts around 160C, a clear liquid forms that gradually changes to a brown colour with continued heating. At about 170C, caramelization occur with the development of a characteristic caramel flavour along with the brown colour.

          Caramelisation is a complex reaction, involving the removal of water and eventual polymerization. Caramel has a pungent taste, is often bitter, is much less sweet than the original sugar from which it is produced, and is non crystalline. It is soluble in water. Fructose caramelizes at 110C and maltose caramelizes at about 180C, galactose at 170C.

         Granulated sugar, when heated in a heavy pan, caramelizes. When hot liquid is added, the caramelized sugar dissolves and can be used to flavour puddings, custards, ice creams, cakes and sauces. Caramel is also produced in making peanut brittle and caramel candy.

7. Decomposition  by alkalies

          The monosaccharides are markedly decomposed by alkalies and flavour may become strong and bitter. Sucrose is least affected by alkalies.

8. Sweetness      

Of the sugars, lactose is the least sweet, followed by maltose, galactose, glucose and sucrose with fructose being the most sweet. A maximum sweetness from fructose is most likely to be achieved when it is used with likely to be achieved when it is used with slightly acid, cold foods and in beverages.

Crystallization

          A crystal is composed of closely packed molecules arranged in a pattern. Crystallization occurs only if the solution is super saturated. The size of the crystals produced will depend on the rate of the formation of nuclei about which the crystals grow and the rate of growth of crystals around the nuclei. If only one or two nuclei are formed, the size of the crystals produced will be large but if the rate of formation of nuclei is very rapid, many small crystals will form. Both the rate of crystallization and the rate of nuclei formation are modified by many factors.

Factors affecting the crystallization of sugar

          In the preparation of fondant, fudge, etc., from super-saturated sugar solutions, crystallization of sugar occurs. The factors affecting the rate of crystallization of sugar and the size of crystals are as follows: (1) Formation of nuclei, (2) Seeding, (3) Concentration of the solution, (4) Temperature, (5) Agitation and (6) Presence of other sugars.

Formation of nuclei: Nuclei can only form from a super-saturated solution. Nuclei form spontaneously in various places in the solution and crystallization begins from these nuclei. The rate of  nuclei formation may be favoured by specks of dust present in the solution. When only a few nuclei develop in the solution, the crystals grow to a large size.

Seeding: When crystals of the same material are added to the solution to start crystallization, the process is called seeding. These crystals serve as nuclei for crystal formation.

Concentration of the solution:  A more super-saturated solution favours the formation of nuclei and crystals. A fondant syrup boiling at 114oC contains more sugar and less water than one boiling at 111oC. Nuclei will form more readily from the more concentration syrup, i.e., the syrup, boiling at 114oC.

Temperature: If crystallization is allowed to occur at high temperature, then coarser crystals are formed. The most favourable temperature for crystal growth in a sugar syrup boiling at 112oC is between 70oC and 90oC. Further, lowering the temperature at 30oC, increases the viscosity of the syrup and retards crystallization. Larger size crystals are formed at higher temperature, while super-saturation and low temperature are conductive for formation of small crystals.

Agitation: Agitation or stirring of the super-saturated sugar solution accelerates the formation of nuclei and helps in the formation of small crystals. Continuous agitation is necessary, till crystallization is complete if a fine textured product is desired.

Presence of other sugars: When glucose or fructose is added to sucrose syrup, crystallization of sucrose is slow. The mixture has a higher solubility and glucose and fructose crystallize less readily than sucrose. A mixture of sucrose, glucose and fructose is formed when sucrose is cooked with acid or acid salts such as citric acid or acid potassium tartrate. Syrups containing 30-45 per cent invert sugar will not crystallize, those containing 16-23 per cent form semi-fluid mass of crystals and those with 6-15 per cent give a plastic mouldable product. Fondants containing 7 per cent invert sugar have a fine texture.

STAGES OF SUGAR COOKERY

Product Temperature (oC)

Stage Description Test

Syrup 110-112 Thread When syrup is dropped from a spoon syrup spins a 5 cm thread

Barfi, fondant fudge

112-115 Soft ball Forms a soft ball when syrup is dropped into cold water; Flattens on removal from H2O

Caramels 118-120 Firm ball

Forms a firm ball when syrup is dropped into cold water; does not flatten on removal from water

Divinity, LaduMarshmellow

120-130 Hard Ball

Forms a ball hard enough to hold its shape when syrup is dropped into cold water.

Butterscotch Toffees

132-143 Soft crack

Forms threads which are hard but not brittle when syrup is

dropped into cold waterBrittle, glaze

150-154 Hard crack

Forms thread which are brittle when syrup is dropped

Barley sugar

160 Clear liquid

Sugar melts`

Caramel 170 Brown liquid

Sugar melts and browns

SUGAR-BOILED CONFECTIONERY

          From boiled sugar solution, two types of confectionery are prepared – crystalline and noncrystalline. The temperature of boiling sugar solution, the ingredients used and the method of handling the supercooled sugar solution determine the nature of the end product.

Crystalline candies (Nonamorphous candies)

          Crystalline candies are chewed easily and they may be cut with a knife.  Sugar is present in the form of very small crystals. Fondant and fudge are two types of crystalline candies.  Crystallization is ensured by adjusting (1) the consistency of sugar syrup to enable the sugar to crystallize (2) to induce crystallization by seeding or agitation and (3) addition of small amounts of other materials which will prevent formation of large  crystals.

          In the case of fondant, small amounts of corn syrup (or) cream of  tartar are used, while in the case of fudge, a mixture of corn syrup and cream (or) corn syrup, milk and butter are used. Such substances prevent the crystal formation.

Fondant : Fondant is prepared from sucrose syrup boiling at 113-115oC . A good fondant should be snowy white in colour, the crystals soft enough to be plastic and velvetty, but not gritty when tasted.

          Fondant can be prepared with the addition of cream of tartar or corn syrup to sugar. The ingredients are sugar – 400 gm, cream of tartar 0.5 gm (or) corn syrup (30 gm), tap water – 200 gm.

The first step in the preparation of fondant is to dissolve the amount of sugar used completely by adding sufficient water. The candy mixture in solution is next concentrated by boiling until it reaches the appropriate doneness. Slow heating resulted in excess acid hydrolysis and many produce too soft a product. The doneness of the candy mixture is determined by measuring the temperature of the

boiling solution. For fondant, it should be 113-115oC.  Another method of measuring doneness in the making of candies is by dropping a small portion of boiling syrup into very cold water, allowing the syrup to cool and evaluating its consistency. In the case of fondant it is the softball shape.

          In the preparation of fondant, at the appropriate stage, the boiled solution is poured on a smooth flat surface and allowed to cool to 40oC. Then it is beaten continuously until it becomes a creamy mass. At first, the mixture becomes cloudy from the air beaten into it and then sets into a stiff mass. A 24 hours ripening period in a tightly covered container softens the crystalline candy slightly and promotes smoothness.

          Fondants are used in confectionery for numerous purposes. They are used to make mints. In this case, the supersaturated sugar mixture in the boiling kettle is cooled to about 71oC and flavoured with mint. The mint quickly solidifies on further cooling. Softened fondant is used in coating fruit and nut mixtures that are moulded and sliced. Fondants are largely used as cream centers of chocolate confectionery.

Fudge :  Fudge is generally prepared from brown sugar. As brown sugar contains a higher percentage of invert sugar than white sugar, sucrose crystallizes less readily. Fudge ripens during storage and becomes soft and velvetty after 24 hr storage.

          The ingredients required for the preparation of fudge is sugar – 200 gm, milk – 120 gm, butter – 14 gm and chocolate – 21 gm. The procedure is as follows : 1) add the chocolate and butter to cooking pan and heat it on a steam bath till the chocolate and butter have melted add sugar. Mix the chocolate and butter well with sugar               (2) Then add milk and heat till the sugar dissolves completely (3) Cook the syrup to a soft ball stage (112oC) (4) Allow it to cool to about 70oC and transfer to a greased moulding pan (5) Cut the candy when it is cool and wrap in butter or foil and store in an air-tight container.

Non-crystalline candies (Amorphons candies)

          Amorphous candies in contrast, have a heterogenous structure and crack into pieces rather than be cut with a knife (eg. toffee and brittles). Caramels, the softest of the amorphous candies, however, may be cut.

          In amorphous candies, sugar is not present in the form of crystals and crystallization of sugar should be prevented by (1) cooking the syrup to a high temperature so that the finished product hardens

quickly before crystals can be formed and (2) adding large amounts of materials like corn syrup, cream, butter etc. which prevent crystallization and make the product plastic and chewy. Amorphous candies are caramels, toffees, brittles and butterscotch. These confections owe their character mainly to the presence of milk, butter and certain vegetable fats.

          Milk solids, when heated in the presence of water and sugars, develop a characteristic flavour due to the reaction between the milk proteins and the reducing sugars. This is known as malliard reaction. Caramelization of a different type also occurs in sugar, glucose and invert sugar when syrups are boiled to temperature of 149 to 157oC. A stronger type of caramelization with yet another flavour is obtained by alkaline treatment, for example, by the reaction of NaHCO3 with boiling syrup at about149oC.

          The action of ammonia on certain reducing sugars also gives ‘caramel colour’. Butter when added to high boiled syrup is subject to some decomposition and gives a characteristic and attractive flavour. Brown sugars, golden syrup and molasses have a flavour that goes well with caramelized milk and these sugars are used a great deal in caramel recipes. 

          The flavour produced by heating milk solids with sugars is related to the method and time of cooking. Sweetened condensed milk is mostly used for the preparation of caramel.  Vegetable fats with suitable emulsifiers (glycerol mono sterate) can be used in place of milk fat (butter) for preparing caramels.

Caramels: Caramels are hard type (or) hard boiled candy, which are not crystalline. To prevent crystallization of sucrose, larger amounts of invert sugar (or) corn syrup are added to sucrose. The temperature at which the syrup should be cooked for obtaining a product of proper texture will depend on the quantity of corn syrup, molasses (or) invert sugar present in the syrup. Addition of milk improves the colour and flavour of caramels. The temperature for caramel preparation is 118-120C.

          The ingredients required for the preparation of caramels are water 750 gm, sugar, white granulated – 1125 gm, sugar brown – 1125 gm, glucose syrup –                1925 gm, sweetened condensed milk 2050 gm, hardened vegetable fat 900 gm, glycerol monosterate – 57 gm and salt – 36 gm.

          All the ingredients are placed in the pan and the mixer set in motion. The gas fire is lighted and heating continued on a low flame

until the sugar is dissolved and the ingredients are completely mixed. Any sugar or other solids that may have accumulated on the sides of the pan above the liquid level are removed. Heating and mixing proceed with the heat increased and the mixture boiling steadily. The level of heating will be obtained by experience, fierce heat will produce scorching on the pan surface and cause dark particles to appear in the mixture. The degree of boil is determined by hand thermometer, which should be kept in hot water before use. The heat is lowered, the mixture stopped, and the thermometer moved quickly through the caramel until the temperature is constant. Boiling is continued and the testing repeated until the thermometer registers 118oC. The fire is turned off, mixing continued for a few minutes, and then the caramel is discharged on a cooling table.

Toffee : Toffees are harder than caramels and therefore are made from syrups cooked at higher temperature. Invert sugar or corn sirup or molasses are added to prevent crystallization of sucrose. Taffies appear white, due to air bubbles present in them. The temperature required is 132-143C.   The manufacture of toffee can be divided into four stages (1) preparation of the raw materials (2) cooking to the desired consistency (3) cooling and cutting into shapes (4) packing. For preparation of the raw materials all the ingredients are mixed in a mixing machine. The chief function of this stage is to bring about emulsification of the fat. Formulation for a quality toffee is sugar – 12 lbs, liquid glucose -8 lbs,   salt-1 tsp, water-1½ qt, hardened coconut – 4 oz, butter -1lb malted milk extract – 1 tablespoonful.

          The mixer used for this purpose generally consists of a horizontal cylindrical vessel, inside which rotates a number of arms fixed along the length of a horizontal axis. Babbles re fixed to break the flow. For loading there is a lid on the top, and for unloading a large diameter hole in the bottom fitted with a closing plate. In some case, raw materials are prepared in the boiling pan prior to cooking.

          In the boiling pan the mixture is cooked rapidly. The temperature of cooking is adjusted between (260-280oF). The stem pressure required for toffee boiling is upwards of 90 lb.

          The toffee from the pans is cooled by pitching on to rectangular cast-iron tables through which cold water can be circulated. Its treatment on the tables varies according to the method of cutting to be adopted. In many cases the toffee is passed through rollers or by “leveling” the still liquid toffee on the tables. If it is to be made into slab toffee, steel frames are forced into the cooling mass and removed when the toffee has set.

          The toffee can be brought to the correct thickness by the use of rollers. The machine used is called a ‘break’. The toffee is poured onto the tubes, not leveled, but allowed to cool until plastic, then passed through the ‘break’ and treated exactly as leveled toffee.

          In the case of roll pieces, they are put into automatic cut and wrap machines which produce 400 pieces of toffee a minute, wrapped in over strip-aluminum foil laminated with waxed paper, cellulose film or waxed paper.

 

Brittles: Brittles are much harder than caramels or toffees. Since the syrup is cooked to a higher temperature than that require for caramels or toffees, slight caramelization of the sugar takes place to impart a characteristic flavour.  Sodium bicarbonate is added in small amounts to syrup to liberate Co2 which gives a porous structure  and glassy appearance to the product (150-154oC). Peanut and cashew nut brittle are commercially prepared and sold in the market.  The ingredients required for the preparation of peanut brittle is sugar – 375 gm, corn sirup (light) – 125 ml, water – 125 ml, Butter – 45 ml, soda – 2 gm, roasted peanut – 375 gm and vanilla essence –          2 gm.

          First combine the water, corn sirup and sugar in a pan. Heat the sugar mixture rapidly to 138oC. Stir as little as possible to keep mixture from scorching, when the syrup reaches 138oC, add the peanuts and the butter. Stir the mixture continuously and heat to 152oC. Remove pan from heat immediately.  Add the soda and the vanilla; stir these ingredients as quickly as possible. Pour the mass on the greased plate, cool it and cut it into desired sizes.

Butter scotch

          Butter scotch has a chewy consistency. It is prepared by boiling a mixture of sugar and corn syrup in the ratio of 4:1 with water till the syrup attains a temperature of 146C. Butter and flavour are then added to the mixture. The ingredients required for the preparation of butter scotch are as follows:.      sugar- 500 g, corn sirup – 125gm, water-150 ml, butter -20 gm, salt- 1.0 gm, oil of lemon -1.0 gm. The method is: Dissolve sugar in water and bring to  146C.Add the butter in small pieces. Add oil of lemon and salt ,while the material is still plastic. Cut it into pieces using a frame cutter. Wrap in waxed foil  or paper.

 

PULSES

Pulses are the edible fruits or seeds of pod bearing plants belonging to the family of Leguminous. The major pulses which find an important place in our dietaries are red gram dhal, bengal gram dhal black gram dhal, green gram dhal and masoor dhal. Some are used as whole grams. Cowpea, rajmah and dry peas also comes under leguminous family.

Composition and nutritive value Principal nutritional characteristics of food legumes1.  Positive factors        High protein content       High lysine content        Excellent supplementary protein to cereal grains2.  Limiting factors       Sulphur amino acid deficiency        Low protein digestibility        Antiphysiological substances

       Trypsin inhibitors        Haemagglutinins        Polyphenolic compounds       Flatulence factors Energy:  Pulses give 340 calories per 100 gm which is almost similar to cereal calorie value.Protein: In a vegetarian diet, pulses are important sources of protein. They give double the amount of protein compared to cereals. They contain chiefly globulins. Albumins can also be seen in pulses.        The protein of pulses are of low quality since they are deficient in methionine and red gram is deficient in tryptophan also. Bengal gram contains higher amounts of arginine and sufficient amount of tyrosine. However pulses are rich in lysine. Hence they can supplement cereal protein. A mixture of cereals and pulses is superior to that of the either one. Legumes are better than cereals as a source of the essential amino acids like isoleucine, leucine, phenylalanine, threonine and valine. Carbohydrates :  Pulses contain 55 to 60 per cent starch. Soluble sugars, fibre and unavailable carbohydrates are also present. The unavailable sugars in pulses include substantial levels of oligosaccharides of the raffinose family (Raffinose, verbascose and stachiose) which produce flatulence in man. These sugars escape digestion due to lack of  -galactosidase activity and digested by the microflora of the lower intestinal tract resulting in the production of large amount of CO2, hydrogen and small amount of methane. Fermentation, germination, cooking, soaking and autoclaving reduce considerable amount of oligosaccharides. Lipids:  Pulses contain 1.5 per cent lipids on moisture free basis. They contain high amounts of polyunsaturated fatty acids. Along with cereals they meet the requirements of essential fatty acids for an adult. Apart from linoleic acid most legume seed oils contain high proportion of linolenic acid.  They undergo oxidative rancidity during storage resulting in loss of protein solubility, off flavour development and loss of nutritive quality, oleic, stearic and palmitic acids are also present. Minerals :  They contain calcium, magnesium, zinc  iron, potassium and phosphorus. 80 per cent phosphorus is present as phytate phosphorus. Phytin complexes with proteins and minerals and renders them biologically unavailable to human beings and animals. Processing such as cooking, soaking, germination and fermentation can reduce or eliminate appreciable amounts of phytin.

Vitamins: Legume seeds are excellent source of B complex vitamins particularly thiamine, folic acid and pantothenic acid. Like cereals, they do not contain any vitamin A or C but germinated legumes contain some vitamin C.  Pulse cookery        Mostly pulses are cooked and consumed and they take longer time to cook than cereals. The cooking process softens that hard seed by improving the plasticity of the cell wall, thus facilitating cell expansion and reduction of intercellular adhesion. Cell cementing material – pectin is altered during cooking so that the cells of the beans separate with comparative ease. Effect of cooking1.     Antinutritional factors:  Uncooked legume seeds contain

antinutritional factors that can be toxic if large amounts are consumed. Trypsin inhibitors and haemagglutinins disappear at about 90 minutes however, polyphenolic compounds although decreasing with time are still found in the cooked material. Relatively high amounts are found in the cooking liquid.

2.     Protein quality: Heating increases protein quality by destroying antinutritional factors, increase digestibility and availability of amino acids. Excess heat reduces the quality of the bean protein.

3.     Vitamins: Loss of thiamine may occur due to the heat applied.

4.     Colour: Sodium metabisulphite is found to be effective in maintaining colour of lentils, other seeds acquired in darker colour processing.

Factors affecting cooking quality        The hardness is of two types, hard shell and sclerema. Hard shell is described as a physical condition in which the seed fails to absorb water. Sclerema takes place in the cotyledons and is induced by various factors:1.     Inherent character:  Some varieties are hard-to-cook

inherently. 2.     Storage condition:  Cooking quality is influenced by time,

temperature and relative humidity during storage. Cooking time for the some hardness increases with storage time. Moisture content during storage is above 10 per cent may cause deterioration in the cooking quality.

3.     Seed maturity :  Cooking time decreases with the increase in seed maturity. The very hard mature seeds take long time to cook.

4.     Dehulling:  This reduces the cooking time and increases digestibility.

5.     Pre cooking:  The cooking time for pre cooked lentil seeds is less compared to untreated ones. Precooking is done by cooking, treating with enzymes and dehydrating in controlled conditions.

6.     Phytin content :  High available phosphorus in the soil contribute to high phytin content in the seed and consequently to good cooking. Phytin has a softening action on peas during cooking by acting as a calcium absorbent, consequently preventing the formation of insoluble calcium pectate.

It is suggested that the softening of peas during cooking takes place through a reaction between sodium/potassium phytate and insoluble calcium/magnesium pectate that converts the latter into the soluble sodium / potassium pectate. Thus cooking quality is related to levels of monvalent elements and to some extent to the ratio of monovalent to divalent elements. No direct relationship is found between phytic acid content in the seed and the cooking quality. 7.     Calcium and magnesium:  Large amounts of insoluble

calcium and magnesium pectates are formed in the middle lamella of the cell walls when the seed is high in calcium and magnesium or when the cooking water is high in these elements. When legumes are cooked in hard water, they take long time to get cooked. Hard water contains chlorides and sulphates of calcium and magnesium salts. They appear to react with pectic substances and phytates and harden the cellulose and delay the cooking of pulses.

8.     Cellulose:  The thickness of the palisade layer and the contents of lignin and alpha cellulose in the seed coats are probably important factors in the cooking quality of pulses. Sodium bi carbonate softens the cellulose and hastens cooking.

It has been proposed that polymerization of polyphenolic compounds in the seed coat where these substances are found and changes in the micro chemical structure of the cotyledons involving carbohydrates-pectic substances. Phytic acid and potassium, calcium and magnesium ions, affect cooking quality.Effect of soaking in water:  Dry legumes have to absorb water before they can be cooked. If legumes are soaked in cold water overnight or in warm water (60-700C) for 4 to 5 hours prior to

cooking, they absorb enough water and can be cooked easily in about 30 to 40 minutes. Germination (or) sprouting       Whole grains are soaked overnight and water should be drained away and the seeds should be tied in a loosely woven cotton cloth and hung. Water should be sprinkled twice or thrice a day. In a day or two germination takes place. Moisture and warmth are essential for germination. Green gram can be germinated in a shorter time. In summer germination process is faster than in winter. Bengal gram, dry beans and dry peas can also be germinated. Advantages:1. (a). During sprouting dormant enzymes get activated and digestibility and availability of nutrients is improved. Starches and proteins are converted to simpler substances. As germination proceeds, the ratio of essential to non essential amino acids changes providing more of essential amino acids. Sprouting reduces trypsin inhibiting factors due to the release of enzymes. Germinated seeds have more of maltose. The action of cytases and pectinases are released during sprouting and the cell walls are broken down and the availability of nutrients increases.

b)    During sprouting minerals like calcium, zinc and iron are released from bound form. Phytic acid amount is reduced so the availability of proteins and minerals are increased.

c)     Riboflavin, niacin, folic acid, choline and biotin content are increased.

d)    Vitamin C is synthesized during germination hence germinated pulses can be substituted for fruits. The increase in Vitamin C is around 7-20 mg per 100 gm of pulses. Vitamin C content is maximal after about 30 hours of germination.2.      Sprouting decreases cooking time. The thick outer coat bursts

open the grain and the grain becomes soft making it easier for the cooking water to penetrate the grain.

3.      Dehusking is easier when the grains are sprouted and dried.4.      Germination decreases the mucus inducing property of

legumes. 5.      Thickening power of starch is reduced due to conversion of

starch to sugars.6.      Germination metabolises oligosaccharides and hence do not

produce gas or flatulence.

7.      Germination improves taste and texture and without much cooking also sprouts like green gram can be consumed.

8.      Germinated pulses add variety to diet.   Antinutritional factors in legumes        Some pulses used in food contain chemical constituents having toxic properties.  1.  Trypsin inhibitor        Trypsin inhibitors are proteins that inhibit the activity of trypsin in the gut and interfere with digestibility of dietary proteins and reduce their utilization. They are generally heat labile. Autoclaving at 1200C for 15-30 minutes inactivates almost all trypsin inhibitors. Trypsin inhibitors are easily inactivated from dhals but more drastic heat treatment is necessary to inactivate trypsin inhibitors of soyabean and kidney bean. 2.  Lathyrism       Lathyrism is a nervous disease that cripples man. This is entirely preventable. The disease is now known to result from an excessive consumption of the pulse Lathyrus sativus (Khesari dhal). It affects young men between the ages of 15 and 45 years.       Lathyrus sativus is grown in dry districts of MadhyaPradesh, Uttarpradesh, Bihar, Bengal, Maharashtra, Mysore and Andhrapradesh.           Throughout the country, it is known by the common name “ Khesari dhal”. The dehusked seeds resemble Bengal gram dhal or red gram dhal.  Hence sometimes khesari dhal is used as adulterant in other dhals. When it is eaten in small quantities lathyrus seeds are valuable as food since it contains 28 per cent protein. But if they are the main source of energy providing more than 50 per cent a severe disease of spinal cord may result. The neurotoxin responsible for lathyrism is -N-Oxalyl-L-, diamino propionic acid. Toxin can be removed by steeping or parboiling.     Steeping process1.     Four times the quantity of seeds is first brought to boil.2.     Seeds are soaked in hot water for two hours.3.     Water should be drained off.4.     The seeds are washed with cold fresh water and sun dried.5.     80 to 90% of the toxin is removed by this method.  Parboiling process

1.     The seeds are soaked in cold water for 12 hours. 2.     Then the seeds are steamed for 20 to 30 minutes. 3.     Again seeds are soaked for one hour and dried. 4.     80 to 90% of toxin leach out by this process.3.  Favism       Favism is a disease characterized by haemolytic anaemia that occurs when individual who are deficient in glucose-6-phophate dehydrogenase consume faba beans or broad beans. In susceptible individuals the level of glutathione in the erythrocytes is also reduced. Three different compounds present in faba beans have been implicated as playing a causative role in the disease. Two of these are glycosides known as Vicine and Covicine and the third is an amino acid derivative known as dihydroxy phenyl alanine- DOPA. These are present only in the cotyledons of the beans, the hulls being essentially free. Germinating and boiling reduce these toxic substances. 4.  Haemagglutinins:  These are proteins in nature and sometimes referred to as phytoagglutins or lectins. They occur widely in leguminous seeds. Haemagglutinins reduce the food intake and resulting in poor growth. Haemagglutinins are heat labile. Haemagglutinins combine with the cells lining the intestinal wall, in almost the same way as it combines with red blood cells thus causing an impairment with the absorption of amino acids. 5.  Cyanogenic glycoside:  Cyanogenic glycosides yield hydro-cyanic acid upon hydrolysis by an enzyme present in the foodstuff. This causes cyanide poisoning by interferring with tissue respiration. On hydrolysis of the glycoside of the enzyme -glycosidase hydrogen cyanide is liberated. Cyanide content in the range of 10-20 mg/100g of pulse is considered safe. Many legumes except lima bean contain cyanide within this limit.   6. Saponins: Saponins produce lather or foam when shaken with water. These are glycosides of high molecular weight. They are present in soyabeans. Saponins cause nausea and vomiting. These toxins can be eliminated by soaking prior to cooking. 7.  Goitrogens  : These substances interfere with iodine uptake by thyroid gland. Thiocyanate, isothiocyanates and their derivatives are present in soyabean, groundnuts and lentils. Excessive intake of these foods in the face of marginal intake of iodine from foods and water may lead to precipitation of goitre.

8.  Tannins:  Tannins are condensed polyphenolic compounds. They are present in high amounts in seed coat of most legumes. Tannins bind with iron irreversibly and therefore interfere with iron absorption. Removal of seed coat of legumes reduce the tannin content. Tannins also bind proteins and reduce their availability. White coat beans have negligible quantity of tannins whereas black and red varieties have higher content of tannins.       

  

NUTS AND OIL SEEDS

          Nuts and oilseeds are seeds or fruits consisting of an edible fat containing kernel and surrounded by a hard or a brittle shell. The nuts and oilseeds are almond, cashewnut, coconut, groundnut, gingelly seeds, mustard seeds, soyabean, walnut pistachio nut, safflower seeds and sunflower seeds.

Nutritive value

          Like pulses, oil seeds and nuts are rich in protein and in addition they contain a high level of fat. Hence they are not only good sources of protein but are concentrated source of energy. They do not contain

an appreciable amount of carbohydrate but contain high level of B-vitamins. Groundnuts are particularly rich in thiamine and nicotinic acid.  Since they are concentrated in fat and protein and also expensive, usually they are not used as main ingredient in cooking and hence may not contribute substantially to the nutrient intake.

Role of nuts and oilseeds in cookerya. Nuts are used fresh, raw, roasted or boiled or salted forms and

also fried forms. b. Nuts are used as thickening agents. Coconut, poppy seeds and

cashewnuts are used as thickening agents in the preparation of gravy.

c. Chutneys can be made and used from nuts e.g. groundnut and coconut.

d. Sweets are made from nuts, e.g. chikki, burfi, kozhukattai, chashewnut cake.

e. Oil is used as cooking media for frying and seasoning. Oil is also used as preservative in pickles.

f. Powders made out of nuts like ground nut and coconut are used as chutneys and salad dressing.

g. Nuts are also used in ice creams, cakes, pastries, payasams and confectionery (chocolate).

h. Nuts are also used in beverages. E.g. badam kheer.i. Peanut butter is used as a topping on the bread or as a side dish

along with chapathis. j. Oil seed cakes are used as weaning food or as thickening agents

in vegetables like capsicum. k. Nuts are used as garnishing material – raw, roasted, salted (or)

boiled forms.

Fats and oils Physical properties 1.    Melting point:  All food fats are mixtures of triglycerides and therefore do not have sharp melting point, but melt over a range of temperatures.

2.    Creaming of fats: Solid fats like butter and margarine can be creamed or made soft and fluffy by the incorporation of air. Fat and sugar are usually creamed together in the preparation of cakes.

3.    Plasticity of fats:  Fats are mouldable and can be creamed to exhibit plasticity. Such fats do not have the ability to flow at room temperature and are thus solid fats. The spreading quality of butter is the result of its plastic nature. Plastic fats are composed of a mixture of triglycerides and not of one kind of a molecule. They

therefore do not have a sharp melting point and are plastic over a fairly wide range of temperature.

4.    Emulsification:  The specific gravity of oils and fats is about 0.9, which indicates that they are lighter than water. Though insoluble in water, they can form an emulsion with water when beaten up with it to form tiny globules in the presence of suitable emulsifying agent. Butter is an emulsion, so also is cream. The presence of minute amounts of milk protein helps to stabilize these emulsions. Lecithin, a phospholipid from egg yolk helps to stabilize mayonnaise, a salad dressing made from vegetable oil. Emulsification of fats is a necessary step in a number of products such as cakes, ice cream and other frozen desserts.

5.    Smoke point:  When fats and oils are heated to a high temperature, decomposition occurs and finally a point is reached at which visible fumes are given off. This is called the smoke point. Fats and oils with low molecular weight fatty acids (those with a short chain length) have low smoke point. If oils with low smoke points are used for deep fat frying purposes, then the food stuff is fried at a lower temperature and thus will take a longer time to acquire the stage of doneness. The factors affect the smoking point of fats and oils are (1) the quantity of free fatty acids present (2) they surface area of oil exposed while heating and (3) the presence of suspended matter (i.e.) repeated use of same sample of oil for frying results in a decrease in its smoke point ultimately in its decomposition.        The smoke point of a fat is partly a matter of its natural composition and partly a matter of the processing it has received. Soyabean, cotton seed, peanut and corn have smoke points at about 230oC. Hydrogenated fats smoke at 221oC to 232oC. Shortening containing monoglyceride as a emulsifier smoke at a lower temperature about 176oC. First, smoke is given off by the emulsifier and later the smoke point may raise from 190o to 193oC.

6.    Hydrogenation:  By this process, liquid fats can be converted into semi solid and solid fats (e.g. Dalda) and to increase the stability of the oils to prevent spoilage from oxidation, which results in undesirable rancid flavour and odours. Plant oils contain a large percentage of unsaturated fatty acids. These unsaturated glycerides in the oil can be converted to more saturated glycerides by addition of hydrogen. This process is known as hydrogenation. Hydrogenated fat is manufactured from vegetable oils by the addition of molecular hydrogen to the double bonds in the unsaturated fatty acids in the presence of nickel, platinum or palladium catalysts under pressure at 300-370oF for a period of 1-3 hours. During hydrogenation, the double bonds present in unsaturated fatty acids taken up hydrogen

and saturated fatty acids result. This hydrogenated fat used as shortening in the preparation of bakery products. They hydrogenated fat has very good keeping quality. They are colourless and odourless.

Chemical properties of fats:  The chemical properties of fats such as iodine value, acid number, and saponification number are useful in that they have been widely used in the identification of different kinds of fats and oils, and in the detection of adulteration of refined oils with other oils that are cheaper and of poorer quality.

Uses/Functions of fats and oils in cookery

          In addition to their nutritional function, oils and fats have other uses which derive principally from their distinct physical properties. They contribute to the tenderness, flavour, colour and texture of food products. They also serve as chief ingredients in preparing foods that form emulsions and as cooking media.

1. Tenderness :  One of the most important function of oils and fats is to tenderize baked products. Large quantities of them find use in the preparation of baked products, such as breads, cakes, biscuits cookies etc. Their function is particularly important in pastry and bread which have little or no sugar to contribute to tenderness. Butter, margarine a blend of vegetable and animal fats, and hydrogenated fats or oils are used as shortening agents.

Fats also contribute to the incorporation and retention of air in the form of small bubbles in the batter. Carbondioxide and steam diffuse into these air cells during baking. Thus, fats contribute to the grain and volume of the baked products.

2.  Flavour: Some fats influence the flavour of the food. Fats that are used for seasonings, table use and salad dressings, possess distinctly pleasing flavours. Ghee and buter when used in the recipe improve the flavour. The ability of fats to take up or dissolve certain aromatic flavour substance is frequently used in food preparation. Onion, ginger, garlic, peppers and other flavourful foods are cooked in oil so initially flavour fruit and other flavours are also   by fat. Butter, margarine, pecan fat and olive oil are commonly used for salad dressings. Cotton seed oil, corn oil, groundnut oil and soyabean oil lack flavour and are used for salad dressing when a bland flavour is required.

3. Texture :  Fats have texture effects in foods. They affect the smoothness of crystalline candies and frozen desserts through the retardation of crystallization and the gelatinization of starch

in starch –thickened mixtures. They contribute to the juiciness of meats and the foam structure of whipped cream.

4. Emulsion:  Fats constitute one of the essential constituents in food emulsions. Prominent among the natural food emulsions are milk, cream and egg yolk. In most food emulsions, oil is the dispersed or discontinuous phase and water is the dispersion medium or continuous phase. For the stabilization of the emulsion, an emulsifying agent is required. Various substances commonly used as emulsifiers are egg yolk, whole eggs, gelatin, starch paste. Vegetable gum, casein and fine powders such as those of paprika and mustard. Salad dressings such as mayonnaise, French dressings and cooked salad dressings are permanent or semipermanent emulsions of oil-in-water.

5. Fat/oil used as medium of cooking:  Fat is used in shallow and deep fat frying. Cooking oil is a better heat transfer medium than air or water in that it heats up very quickly because of its greater specific heat, and its operating temperature of about 200oC is considerably higher than that of water.

Pan frying is used to cook dosas, chapathis, omelettes, cutlets and tikkis. In pan frying, the amount of fat used can be limited.

Deep fat frying method is used in preparing pooris, vadas, cutlets, bajjis and pakodas. In deep fat frying, there is direct transfer of heat from the hot fat to the cold food that continues until the food is cooked. Water is lost from the exterior surface of the food as it is converted the steam. The steam carries of energy from the surface of the food and prevents charring.

Changes in fats due to heat during cooking:         Several changes occur in fats and oils during frying of

foods. Some of the changes are (a) increasing in free fatty acids (b) decrease in iodine value (c) increase in peroxide value and carbonyl, (d) reduction in the content of polyunsaturated fatty acids (e) formation of polymers (f) increase in viscosity.

 Free fatty acids: The free fatty acids content increases during heating. Moisture present in the food material fried tends to hydrolyse the fat and increase the free fatty acid content.

Iodine value:       The iodine value decreases as a result of heat treatment. The decrease is due to the formation of dimers, polymers and epoxides at the double bond.

Peroxides and carbonyls:The peroxide formed are unstable and yield volatile aldehydes, ketones alcohols and acids.

Polymerisation of unsaturated fatty acids: During the thermal oxidation of fats, there is considerable isomerisation of double bonds. Epoxides are formed and cleavage products of fatty acids are formed. Some of the cleavage products are not volatile and are called monomers. Hydroxy fatty acids are formed. Cyclic compounds having benzene nucleus are also formed. More complicated compounds known as dimers and polymers are also formed. The content of polyunsaturated fatty acids decreases as a part of it undergoes polymerization.

Increase in viscosity :  The viscosity of heated oil increases due to the formation of cyclic compounds and polymerized products.

Factors affecting amount of fat absorbed during frying

          The chief factors influencing the amount of fat absorbed by fried foods are (1) the temperature and time of cooking (2) the total surface area of the food (3) the moisture content of the food  (4) the protein, carbohydrate and fat contents of the food and (5) smoking temperature of the fat.

1.     Temperature and time of cooking : When doughnuts were fried at 170oC, 185oC and 200oC the time required for frying at 170oC was greater than at 200oC. Consequently, the amount of fat absorbed was also greater.

2.     Total surface area:  Studies with frying of doughnuts have shown that doughnuts having a greater surface area absorbed more fat than doughnuts with smaller surface area.

3.     Moisture content of the dough: Studies with frying poories and vadas have shown that if the moisture content of the material is highest, the fat absorption is also greater than the control.

4.     Protein, fat and carbohydrate contents:  Studies with doughnuts showed that if doughnuts are made of hard wheat flour having more protein, they absorbed less fat than doughnuts made out of soft wheat flours containing less protein. Foods containing more fat, e.g. pork chops absorb less fat than lean fish during frying.

5.     Smoking temperature of fat:  Studies with doughnuts showed that fat absorption was greater when doughnuts were fried in fats

having lower smoking temperature and containing higher amounts of free fatty acids.

Rancidity in fats

          The development of off-flavours in fats is known as rancidity. There are three main types of rancidity. (a) Hydrolytic (b) oxidative and (c) ketonic.  

a.  Hydrolytic rancidity:    Hydrolysis of fat by lipase need not always produce off-flavours. Incase of butter fat and coconut oil, butyric acid and other low molecular weight fatty acids are set free by hydrolysis by lipase. The odours of these acids contribute largely to the smell of rancid butter. The higher fatty acids such as palmitic and stearic acids have little odour.

b. Oxidative rancidity :  This is the common type of rancidity observed in all fats and oils. The oxidation takes place at the unsaturated linkage. Certain metals, e.g. copper, hasten the onset of oxidative rancidity. The addition of oxygen to the unsaturated linkage results in the formation of peroxide value, which on decomposition, yields aldehydes and ketones having pronounced off-flavour.

c. Ketonic rancidity :  This type is most frequently encountered as a result of action of fungi such as Aspergillus niger, pencillium glaucum on coconut or other oil seeds. They tallowy odour developed may be due to aldehydes and ketones formed by the action of the enzymes present in the fungi on oils.

Factors affecting the development of rancidity

          The rate at which oxidation occurrs varies with the degree of unsaturation and the conditions of storage. The other factors which influence the rates of oxidation are certain metals (e.g., copper), light, temperature of storage, moisture content and presence of lipoxidases.

Metals: Certain metals e.g. copper, even when present in traces (2 ppm) accelerates the development of rancidity. Lead, iron and zinc are moderately active while tin and aluminium are the least active of the metals studied. Copper is 20 times as active as iron as a pro-oxidant.

Lipoxidase: These enzymes are present in some food stuffs., e.g., oilseeds, cereals etc. and they accelerate the oxidation of fatty acids containing 1-4 pentadiene system.

Light:  Light accelerates the development of rancidity when the fat is exposed to light as such or in white transparent bottles.

Moisture:  The moisture content of the product may affect the rate of development of oxidative rancidity. For example, biscuits with 2% moisture content develop oxidative rancidity more rapidly than biscuits with 3-5% moisture content.

Temperature:  Rancidity develops more rapidly with increase in the temperature of storage e.g. products stored at 37oC develop rancidity more rapidly than products stored at 10oC.

Prevention of rancidity

          Fats can be protected against the rapid development of rancidity by controlling the conditions of storage.

1.     Storage at refrigerator temperature prevent rancidity. 2. Rays of light catalyse the oxidation of fats. By the use of

coloured glass containers  that absorb the active rays, fats can be protected against spoilage. Certain shades of green bottles and wrappers and yellow transparent cellophane wrappers are effective in preventing rancidity.

3. Vacuum packaging also helps to retard the development of rancidity by excluding oxygen.

4. Antioxidants naturally present in the food such as vitamin C, beta carotene and vitamin E protect against rancidity.

5. Antioxidants can also be added like butylated hydroxy anisole (BHA), butylated hydroxy toluene (BHT), tertiary butyl hydroquinone (TBHQ) and propyl gallate.

6. Substances like citric acid may be used along with antioxidants in foods as synergists. A synergist increases the effectiveness of an antioxidant but is not as effective an agent when used alone. Some synergists may be effective because of their ability to bind or chelate the metals and prevent them catalyzing the oxidation process. Chealting agents are sometimes called sequestering agents. 

 

 

MILK

 Composition of milk:

          Milk from different sources, regardless of breed or even species, will contain the same classes of constituents. They are milk fat (3-6%), protein (3-4 %), milk sugar (5%) and ash (0.7%). Water accounts for the balance of 85.5-88.5%. All the solids in milk are referred to as ‘ total solids’ (11.4 – 14.5%) and the total solids without fat is known as ‘milk solids – non fat’ (MSNF) or  ‘ solids – not-fat’. The composition of milk from various sources include Buffalo, Cow, Goat, Human and Ass. The yield of milk and its composition, from the same source, vary depending upon many factors. These include the breed of the animal, its age, the stage of lactation, time of milking, time interval between milking, season of the year, feed of the animal condition of the animal and so on.

Milk fat

          Milk fat or butter fat is of great economical and nutritive value. The flavour of milk is due to milk fat. It exists in milk in the form of minute globules in a true emulsion of oil-in-water type, the globules being the dispersed phase. The fat globules are invisible to the naked eye, but are readily seen under a microscope. Each globule of fat is surrounded by a very thin layer of protein, phospholipids and neutral lipids.

          Fat globules vary widely in size from 2 to 10 m, and in numbers 3 x 109/ml. Milk fat is a mixture of several different glycerides. Other lipid materials present in milk are phospholipids, sterols, free fatty acids, carotenoids and fat soluble vitamins. Carotenes are responsible for the yellow colour of milk fat.

Milk proteins

Casein : Casein constitutes 80% of the total nitrogen in milk. It is precipitated on the acidification of milk to pH 4.6 at 20oC. The remaining whey protein constitutes lactoglobulin and lactalbumen. Milk protein contains proteoses, peptones and milk enzymes.

          Casein is also a glycoprotein. The calcium content of whole casein is about 8.2%, carbohydrates are present to the extent of 5.7% in casein. Glutamic acid is the predomiant one in casein. Proline, aspartic, leucine, lysine and valine are also present. Casein is a good source of essential amino acids.

          Casein can also be separated from the milk by the addition of rennin an enzyme secreted by the young calves.

Why proteins: Whey protein constitutes lactoglobulin and lactalbumin. These are not precipitated by acid or rennin, they can be coagulated by heat. Whey also contains small amounts of lactoferrin and serum transferrin.

Milk sugar: The chief carbohydrate present in milk is lactose or milk sugar is a disaccharide, although trace amounts of glucose, galactose and other sugars are present. Lactose gives on hydrolysis glucose and galactose. Lactose has only one sixth the sweetness of sucrose and one third – one fourth of its solubility in water. When milk is heated lactose reacts with protein and develops a brown colour. The development of brown colour is due to non-enzymatic browning. It is called Maillard reaction. Reducing sugar reacts with the amino acid lysine and brown colour develops. As the amino acid lysine is involved the quality of protein is decreased. The brown colour in condensed milk, khoa, basundi and gulabjamun is due to maillard reaction.

          Lactose is acted upon by bacteria to produce lactic acid. The acid produced by the action of intestinal microorganisms on lactose checks the growth of undesirable putrefactive bacteria and promotes absorption of minerals. The acid fermentation is used in making butter, cheese and curd. 

Ash and salts: Milk ash is a white residue remaining after incineration of milk at 600oC. It consists of oxides of sodium, potassium, calcium, magnesium, iron, phosphorus and sulphur, plus some chloride. In addition to these, milk contains many trace elements like copper, zinc, aluminium ,molybdenum, iodine etc., depending upon the feed of the animal.

          The salts of milk are phosphates, chlorides, and citrates of sodium, potassium, calcium and magnesium. Milk is a rich source of calcium. The calcium, phosphorus ratio (1:2:1) in milk is regarded as most favourable for bone development. In addition, dairy products contain other nutrients such as vitamin D and lactose which favour calcium absorption. The calcium requirement cannot be met easily without taking milk.

Enzymes: The enzymes present in milk is alkaline phosphatase, lipase, xanthin oxidase, catalase and lactoperoxidase.

Vitamins: Thiamine occurs in only fair concentration in milk, but is relatively constant in amount. Riboflavin is present in a higher concentration in milk than the other  B-vitamins and its stability to heat makes milk a dependable source of this vitamins. Milk is  not a good source of niacin but it is an excellent source of tryptophan. Milk is very

poor source of vitamin C. The amount of fat soluble vitamins depend on the feed of the animal.

Colour: The yellowish colour of milk is due to the presence of carotene and riboflavin. The fat soluble carotenes are found in the milk fat; the riboflavin is water soluble which can be visible clearly in whey water.

Use/Role of milk and milk products in cookery

1.      It contributes to the nutritive value of the diet., e.g. milk shakes, plain milk, flavoured milk, cheese toast.

2.      Milk adds taste and flavour to the product e.g. payasam, tea, butter to toast.

3.      It acts as a thickening agent along with starch, e.g., white sauce or cream soups.

4.      Milk is also used in desserts., e.g. ice cream, puddings.5.      Curd  or butter milk is used as a leavening agent and to

improve the texture e.g. dhokla, bhatura. 6.      Curd is used as a marinating agent, e.g. maintaining chicken

and meat.7.      Cur is used as a souring agent, e.g. rava dosa, dry curd

chillies.8.      Khoa is used as a binding agent, e.g. carrot halwa.9.      Milk and curd increases shelf life poories preserve better when

the dough is mixed with milk / curd. 10. To prevent browning in vegetables, e.g. butter milk is used for

preventing browning when plantain stem is cut.11. Variety to the diet., e.g. butter milk sambar, avial   and butter 

paneer.12. Cheese is used as garnishing agent.13. Milk is used as clarifying agent in sugar syrup.14. Salted buttermilk is used for quenching thirst.

Points to be remembered in using milk and milk products in cookery

1.     Prevention of scorching:  Too thin vessels and too high a temperature can scorch the milk at the bottom of the vessel . Use double boiler or stir constantly and continuously.

2.     Prevention of curdling in fruit milk beverages: Fruit and milk are cooled thoroughly as high temperature favour curdling. Raw pineapple contain pomelin and may lead to curdling of milk.

3.     Prevention of curdling in fruit custard: This can be done by adding ripe (or) canned fruits. Some fruits like grapes and pineapples may curdle custard.

4.     Prevention of scum formation can be achieved by covering the pan, stirring, using milk cooker, or by adding whipped cream.

5.     Prevention of curdling in tomato soups: This can be done by adding tomato juice to the white sauce.          

 

Enzymatic browning

          Browning can be observed on the cut surfaces of light coloured fruits and vegetables such as apples, banana, potatoes and brinjal due to enzymatic action is known as enzymatic browning. Normally, the natural phenolic compounds present in intact tissues do not come in contact with the phenol oxidase present in some tissues. When the tissue is injured or cut and the cut surfaces is exposed to air. Phenol oxidase enzymes released at the surface act on the polyphenols present oxidizing them to Orthoquinones. The orthoquinones rapidly polymerize to form brown pigments. Tyrosine, Chlorogenic acid, the various catechins and several mono and dihydroxy phenols are among the many compounds that can serve as substrates for oxidation by polyphenoloxidase to cause browning or other discolouration in these foods.

Polyphenols involved in browning

flavanols, catechins, tannins, cinnamic acid derivatives Tea

chlorogenic acid, caffeic acid, caffeylamideSweet potato

tyrosine Shrimp

chlorogenic acid, caffeic acid, catechol, DOPA, p-cresol, p-hydroxyphenyl propionic acid, p-hydroxyphenyl pyruvicacid, m-cresol

Potato

chlorogenic acid, catechin, caffeic acid, catechol, DOPA Plum

chlorogenic acid, catechol, catechin, caffeic acid, DOPA, 3,4-dihydroxy benzoic acid, p-cresol Pear

chlorogenic acid, pyrogallol, 4-methyl catechol, catechol, caffeic acid, gallic acid, catechin, dopamine Peach

tyrosine, catechol, DOPA, dopamine, adrenaline, noradrenalineMushroom

dopamine-HCl, 4-methyl catechol, caffeic acid, catechol, catechin, chlorogenic acid, tyrosine, DOPA, p-cresol Mango

tyrosine Lobster

tyrosine, caffeic acid, chlorogenic acid derivatives Lettuce

catechin, chlorogenic acid, catechol, caffeic acid, DOPA, tannins, flavonols, protocatechuic acid, resorcinol, hydroquinone, phenol

Grape

chlorogenic acid, caffeic acid, coumaric acid, cinnamic acid derivatives Eggplant

chlorogenic acid, caffeic acid Coffee beans

catechins, leucoanthocyanidins, anthocyanins, complex tannins Cacao

3,4-dihydroxyphenylethylamine (Dopamine), leucodelphinidin, leucocyanidinBanana

4-methyl catechol, dopamine, pyrogallol, catechol, chlorogenic acid, caffeic acid, DOPA Avocado

isochlorogenic acid, caffeic acid, 4-methyl catechol, chlorogenic acid, catechin, epicatechin, pyrogallol, catechol, flavonols, p-coumaric acid derivatives

Apricot

chlorogenic acid (flesh), catechol, catechin (peel), caffeic acid, 3,4-dihydroxyphenylalanine (DOPA), 3,4-dihydroxy benzoic acid, p-cresol, 4-methyl catechol, leucocyanidin, p-coumaric acid, flavonol glycosides

Apple

Phenolic substrates Source

Enzymic browning is beneficial for

• Developing flavor in tea (here the reaction is incorrectly called fermentation)

• Developing color and flavor in dried fruit such as figs and raisins.

Enzymic browning is detrimental to

• Fresh fruit and vegetables, in particular apples and potatoes

• Seafood such as shrimp

Prevention of enzymatic browning 

          The methods commonly used for the prevention of enzymatic browning are the following:

1.  Thermal in activation of polyphenolase: The most commonly used method is blanching i.e. heating in live steam. The enzyme is fairly heat-stable and requires to be heated at 100oC for 2 to 10 min. for complete inactivation. This may not be possible in practice as cooking for long periods will affect the flavour and texture of the fruit or vegetable. Further, blanching breaks the cellular structure and brings about the contact of the enzyme with the substrate. If the thermal destruction is not complete or rapid, the high temperature may accelerate browning.

2.  Changes of pH using acids: The optimal pH for polyphenolase activity is between 6.0 and 7.0. Lowering of the pH to 4.0 by the addition of citric acid inhibits the phenolase activity. It is also possible citric acid reacts with the copper present in the enzyme. Malic acid also has been found to be effective.

3.  Use of antioxidants: Ascorbic acid retards browning by virtue of its reducing power. It reduces 0-quinones formed to the parent o-diphenols. Ascorbic acid is used along with citric acid to prevent browning in fruit products. SO2, sulphites and bisulphites inhibit effectively browning.

4.  Prevention of contact with oxygen: a)Using controlled / modified atmosphere packaging for the processed foods i.e. packaging the product under nitrogen prevents surface browning effectively. b)Contact with oxygen can be reduced by immersing the fruits in water or liquids like milk, curd, fruit juice or honey or sugar solution or sodium chloride solution after cutting or by covering with a wet cloth.  

Inhibitors of enzymatic browning : 

Category Example of inhibitor Mode of action

Reducing agents

sulphiting agentsascorbic acid and analogscysteineglutathione

Removal of oxygen

Chelating agents

phosphates EDTA organic acids

Removal of metals (most PPO enzymes contain metal atoms)

Acidulants citric acid phosphoric acid

Reducing pH

Enzyme inhibitors

Aromatic carboxylic acidspeptidessubstituted resorcinols

React with enzymes

NON – ENZYMATIC BROWNING

          The formation of brown discolouration in foods during heat processing and storage is known as nonenzymatic browning. Four mechanisms are involved in non-enzymatic browning in foods.

1. Maillard reaction  involving interaction between reducing sugars, amino acids and proteins

2. Reaction of oxidation products of ascorbic acid with proteins or amino acids.

3. Reaction of oxidation products of polyunsaturated fatty acids with amino acid and proteins and

4. Caramelization of sugars.    

1. Reaction between reducing sugars and amino acids (or) proteins

          The steps involved in the maillard reaction between reducing sugars and amino acids (or) proteins are as follows :- a) Condensation of the aldehyde or ketone group with the amino group. b) rearrangement of condensation products. c) dehydration of   rearrangement products d) further degradation and e) polymerization to brown pigments. The monosaccharides, ie. glucose, fructose etc., react faster with aminoacids than the disaccharides – maltose and lactose. Sucrose does not react by itself as it has no reacting group but

the hydrolytic products of sucrose ie., glucose and fructose react with amino acids.

2. Reaction of oxidation products of ascorbic acid with amino acids (or) proteins

          Ascorbic acids is responsible for the development of browning reactions in fruit juices, and concentrates and in canned vegetables. Mixtures of ascorbic acid and amino acids develop brown colour more rapidly than mixtures of reducing sugars and amino acids. Dehydroascorbic acid is highly reactive and can react with amino acids. In the decomposition of ascorbic acid or dehydro ascorbic acid, the following products which are highly reactive are formed;  a) Furfural and b) ozone of L-xylose.

3. Reaction between oxidation products of polyunsaturated fatty acids and amino      acids.

          When polyunsaturated fatty acids undergo oxidation, the hydroperoxides formed are broken down to aldehydes and ketones. One of the main products of autoxidised polyunsaturated fatty acids is malonaldehyde.  This reacts with amino acids and proteins yielding coloured products. Malonaldehyde and other aldehydes and ketones formed by the degradation of polyunsaturated fatty acids react with the end amino group of lysine in the protein leading to the development of brown colour.  

4. Browning due to caramelization of sugars

          Sugars can undergo browning in the absence of amino acids by the process of caramelization but this reaction requires a high temperature of over 160C.

Conditions for the browning reactions

          The factors affecting the reaction of reducing sugars or oxidation products of ascorbic acid (or) polyunsaturated fatty acids with proteins (or) amino acids are : 1) pH of the medium 2) Temperture and 3) Moisture content.

pH

          The maillard reaction occurs in neutral or slightly acid or alkaline pH. The reaction is faster in neutral or slightly alkaline medium than in slight acid medium.

Temperature   

          The reaction does not takes place at very low temperature (0C). As the temperature is raised, the reaction velocity increases, a linear relationship exists between the rate of reaction and temperature over a range of 30 – 90C.

Moisture

          The reaction does not take place at low moisture levels ie., 3 to 4% moisture. The optimal moisture levels for the reaction range from 10 to 15% in a dehydrated product. 

Prevention of non-enymatic browning

          The browning reactions can be prevented or retarded by the following procedures: a) storing the material at low temperature 0-5C. 2) keeping the moisture content of dry products below 4-0%. 3) excluding oxygen in the case of products containing ascorbic acid and fat to prevent their oxidation and 4) addition of SO2 or bisulphite in the case of dehydrated vegetables and fruits.

Effect on nutritional quality

          The development of browning reaction in protein – rich foods such as skim milk powder, fish meal, egg powder etc., lead to the loss of available lysine due to the reaction of the end amino group of lysine with the reducing sugars. The reduction in the available lysine content will lower the nutritive value of the proteins. Good correlation has been found between the available lysine content and protein efficiency ratio of the proteins in processed foods.

 MILK 

Composition of milk

          Milk from different sources, regardless of breed or even species, will

contain the same classes of constituents. They are milk fat (3-6%), protein (3-4

%), milk sugar (5%) and ash (0.7%). Water accounts for the balance of 85.5-

88.5%. All the solids in milk are referred to as ‘ total solids’ (11.4 – 14.5%) and

the total solids without fat is known as ‘milk solids – non fat’ (MSNF) or  ‘ solids –

not-fat’. The composition of milk from various sources include Buffalo, Cow,

Goat, Human and Ass. The yield of milk and its composition, from the same

source, vary depending upon many factors. These include the breed of the

animal, its age, the stage of lactation, time of milking, time interval between

milking, season of the year, feed of the animal condition of the animal and so on.

Milk fat

          Milk fat or butter fat is of great economical and nutritive value. The flavour

of milk is due to milk fat. It exists in milk in the form of minute globules in a true

emulsion of oil-in-water type, the globules being the dispersed phase. The fat

globules are invisible to the naked eye, but are readily seen under a microscope.

Each globule of fat is surrounded by a very thin layer of protein, phospholipids

and neutral lipids.

          Fat globules vary widely in size from 2 to 10 m, and in numbers 3 x

109/ml. Milk fat is a mixture of several different glycerides. Other lipid materials

present in milk are phospholipids, sterols, free fatty acids, carotenoids and fat

soluble vitamins. Carotenes are responsible for the yellow colour of milk fat.

Milk proteins

Casein : Casein constitutes 80% of the total nitrogen in milk. It is precipitated on

the acidification of milk to pH 4.6 at 20oC. The remaining whey protein constitutes

lactoglobulin and lactalbumen. Milk protein contains proteoses, peptones and

milk enzymes.

          Casein is also a glycoprotein. The calcium content of whole casein is about

8.2%, carbohydrates are present to the extent of 5.7% in casein. Glutamic acid is

the predomiant one in casein. Proline, aspartic, leucine, lysine and valine are

also present. Casein is a good source of essential amino acids.

          Casein can also be separated from the milk by the addition of rennin an

enzyme secreted by the young calves.

Why proteins: Whey protein constitutes lactoglobulin and lactalbumin. These

are not precipitated by acid or rennin, they can be coagulated by heat. Whey also

contains small amounts of lactoferrin and serum transferrin.

Milk sugar: The chief carbohydrate present in milk is lactose or milk sugar is a

disaccharide, although trace amounts of glucose, galactose and other sugars are

present. Lactose gives on hydrolysis glucose and galactose. Lactose has only

one sixth the sweetness of sucrose and one third – one fourth of its solubility in

water. When milk is heated lactose reacts with protein and develops a brown

colour. The development of brown colour is due to non-enzymatic browning. It is

called Maillard reaction. Reducing sugar reacts with the amino acid lysine and

brown colour develops. As the amino acid lysine is involved the quality of protein

is decreased. The brown colour in condensed milk, khoa, basundi and

gulabjamun is due to maillard reaction.

          Lactose is acted upon by bacteria to produce lactic acid. The acid

produced by the action of intestinal microorganisms on lactose checks the growth

of undesirable putrefactive bacteria and promotes absorption of minerals. The

acid fermentation is used in making butter, cheese and curd. 

Ash and salts: Milk ash is a white residue remaining after incineration of milk at

600oC. It consists of oxides of sodium, potassium, calcium, magnesium, iron,

phosphorus and sulphur, plus some chloride. In addition to these, milk contains

many trace elements like copper, zinc, aluminium ,molybdenum, iodine etc.,

depending upon the feed of the animal.

          The salts of milk are phosphates, chlorides, and citrates of sodium,

potassium, calcium and magnesium. Milk is a rich source of calcium. The

calcium, phosphorus ratio (1:2:1) in milk is regarded as most favourable for bone

development. In addition, dairy products contain other nutrients such as vitamin

D and lactose which favour calcium absorption. The calcium requirement cannot

be met easily without taking milk.

Enzymes: The enzymes present in milk is alkaline phosphatase, lipase, xanthin

oxidase, catalase and lactoperoxidase.

Vitamins: Thiamine occurs in only fair concentration in milk, but is relatively

constant in amount. Riboflavin is present in a higher concentration in milk than

the other  B-vitamins and its stability to heat makes milk a dependable source of

this vitamins. Milk is  not a good source of niacin but it is an excellent source of

tryptophan. Milk is very poor source of vitamin C. The amount of fat soluble

vitamins depend on the feed of the animal.

Colour: The yellowish colour of milk is due to the presence of carotene and

riboflavin. The fat soluble carotenes are found in the milk fat; the riboflavin is

water soluble which can be visible clearly in whey water.

Use/Role of milk and milk products in cookery

1.      It contributes to the nutritive value of the diet., e.g. milk shakes, plain

milk, flavoured milk, cheese toast.

2.      Milk adds taste and flavour to the product e.g. payasam, tea, butter to

toast.

3.      It acts as a thickening agent along with starch, e.g., white sauce or

cream soups.

4.      Milk is also used in desserts., e.g. ice cream, puddings.

5.      Curd  or butter milk is used as a leavening agent and to improve the

texture e.g. dhokla, bhatura.

6.      Curd is used as a marinating agent, e.g. maintaining chicken and meat.

7.      Cur is used as a souring agent, e.g. rava dosa, dry curd chillies.

8.      Khoa is used as a binding agent, e.g. carrot halwa.

9.      Milk and curd increases shelf life poories preserve better when the

dough is mixed with milk / curd.

10. To prevent browning in vegetables, e.g. butter milk is used for preventing

browning when plantain stem is cut.

11. Variety to the diet., e.g. butter milk sambar, avial   and butter  paneer.

12. Cheese is used as garnishing agent.

13. Milk is used as clarifying agent in sugar syrup.

14. Salted buttermilk is used for quenching thirst.

Points to be remembered in using milk and milk products in cookery

1.     Prevention of scorching:  Too thin vessels and too high a temperature

can scorch the milk at the bottom of the vessel . Use double boiler or stir

constantly and continuously.

2.     Prevention of curdling in fruit milk beverages: Fruit and milk are cooled

thoroughly as high temperature favour curdling. Raw pineapple contain

pomelin and may lead to curdling of milk.

3.     Prevention of curdling in fruit custard: This can be done by adding ripe

(or) canned fruits. Some fruits like grapes and pineapples may curdle

custard.

4.     Prevention of scum formation can be achieved by covering the pan,

stirring, using milk cooker, or by adding whipped cream.

5.     Prevention of curdling in tomato soups: This can be done by adding

tomato juice to the white sauce.

VEGETABLES

Classification

          Vegetables are classified on the basis of the parts consumed of plants,

such as roots, stems, leaves, flowers etc. This is not satisfactory as some parts

of plants may be grouped under more than one heading. Vegetables can be

divided into two main groups: winter or rabi vegetables and summer or kharif

vegetables according to their growing seasons. They are further sub divided into

groups based on their cultural requirements. On this basis, the commonly used

vegetables can be classified as follows:

1 Cole crops - Cabbage, cauliflower, knol-khol,Brussels sprouts,

chineese cabbage ,broccoli

 

2 Root

vegetables

- Carrot, parsnip, radish, turnip, beet root

3 Fruit vegetables - Tomato, bell pepper, egg plant,okra

4 Cucurbits   Cucumber, pumpkin, squash gourds

5 Leafy

vegetables

- Spinach, lettuce, amaranthus, celery, fenugreek etc.

6 Tuber crops - Potato, sweet potato, tapioca

7. Bulbs - Onion, garlic, leek

8. Perennial

vegetables

- Asparagus, rhubarb, globe artichoike

9. Leguminous

vegetables

- Peas, beans

 Composition

          Vegetables differ widely in their chemical composition. Vegetables, as a

group have a high water content, particularly in the greens. The crispness of

greens depends on the water in the cells. Partial dehydration of cells results in a

change from a crisp to a limp leaf. The protein value of a vegetable is very low

except with legumes. The carbohydrates present in vegetables are cellulose,

starch and sugars. Cellulose, with hemicellulose and pentosans, forms the

structural material of vegetables. Peetic substances, the cementing material are

between the cell walls of vegetables. Some vegetables like potato and tapioca

contain a high percentage of carbohydrates as starch. In immature vegetables

this carbohydrate is mostly in the form of sugar and gradually changes to starch

as the vegetables matures. Vegetables contain nonvolatile acids, such as citric,

malic, oxalic acid and succinic acids. These contribute to the flavour of

vegetables. The very strong flavour characteristics of some vegetables like

onion, garlic, cauliflower etc., is due to certain sulphur – containing volatile

compounds. 

          Vegetables contain various chemical compounds responsible for the wide

range of colours in their raw and cooked condition. The pigment of the green

vegetables is due to chlorophyll. The yellow and orange colour of vegetables

such as carrots and tomatocs, are on account of carotenoids. Flavonoids are

responsible for the colour of radish and red cabbage.

Nutritive value

          The nutritive value of different vegetables vary sufficiently and it is wise to

serve a variety of vegetables to ensure that all the necessary nutrients from the

vegetable category are included in the diet. Vegetables as a group contribute

indigestible fibre, minerals and vitamins to the diet. Most vegetables, except

those containing starch which provide a useful source of energy, are low in

calories. Leguminous vegetables provide proteins which, through, are incomplete

owing to the limited quantities of essential amino acids. Vegetables are very low

in fat content and this is also responsible for their low calorific content.

          Calcium and iron are two minerals found in significant amounts in

vegetables. Green leafy vegetables and legumes contain these minerals in good

quantity. However, in some vegetables eg., spinach, the calcium combines with

oxalic acid present in the vegetable forming the insoluble calcium oxalate which

cannot be absorbed by the body. Vegetables also supply the other essential

mineral required by the body.

          Vegetables are good sources of vitamin A and C. Orange and dark green

leafy vegetables are rich in carotenes which are precursors of vitamin A. The

leafy vegetables are also rich sources of vitamin C. Green peppers, brussel

sprouts tomatoes etc., are good sources of ascorbic acid. The indigestible fibre

content of vegetables contributes to the roughage promoting the mobility of the

food through the intestine.

COOKING OF VEGETABLES

Why Cook Vegetables?

          Many vegetables are improved in palatability and are more easily and

completely digested when cooked. Some vegetables such as dried legumes

could not be mastigated or digested in the raw state. The flavours of cooked

vegetables are different from those of raw vegetables and are sometimes more

desirable.

          The protein of dried legumes is improved in quality by heat, and some of

the minerals and vitamins, particularly of soy beans are rendered more available

after the beans are heated.

          All vegetables have a frame work consisting largely of cellulose and

hemicellulose materials cemented or held together by other materials, including

in large parts, the pectic substances. In the network of cells is embedded much

of the nutritive material of the plant, such as starch granules, although some

soluble nutrients are dissolved in the plant juices. Cooking is necessary to

gelatinize starch and increase its digestibility.

Changes during cooking

Changes in texture

          Cellulose in vegetables is slightly softened by cooking and the amount of

hemicellulose is somewhat reduced. Although cellulose is practically indigestible

in the human digestive treat, some studies indicated that there is a slight

increase in the utilization of cellulose after cooking. Sodium bicarbonate (baking

soda) added to the cooking water tends to disintegrate the cellulose and to

produce a soft texture in a short cooking period. Acid, on the other hand, tends to

produce firmness of texture.

          The pectic substances in the intercellular cementing material may be

changed on cooking so that there is some cell separation. Calcium chloride or a

saturated solution of calcium hydrobide. (lime water) has the effect of making

vegetable tissues more firm, probably by firming insoluble calcium salts with

pectic substances in the plant tissue. The former is used commercially to help

preserve the firmness of tomatoes, and possibly other foods during canning.

Calcium choloride may also be used to make melon rinds firm and brittle for

processing or pickling.

Changes in flavour : Flavour is affected in various ways during cooking. Over

cooking often brings about decomposition, which adversely affects flavour. A

covered kettle or steamer tends to increase the intensity of flavour, whereas an

open kettle allows some volatile flavour substances to escape. A large amount of

cooking water extracts more flavour substances than does a small amount of

water. Sugars, acids and some minerals that contribute to flavour are water

soluble.

          The flavour of the sulfur – containing vegetables may be marred by the

decomposition of sulfur compounds and during cooking. Dimethyl disulfide from

the amino acid S-methyl – L – cysteine sulfoxide makes an important contribution

to the flavour of cooked cabbage. In over cooked vegetables of the cabbage

family hydrogen sulfide and other volatile sulfur compounds may give an

unpleasant flavour and odour. Vegetable acids may aid in the decomposition.

Leaving the lid off for the first part of cooking to allow some volatile acids to

escape may help to control these changes. However, probably more important is

cooking sulfur containing vegetables for the shortest time possible to give

tenderness before substantial decomposition of sulfur compounds occurs.

Vegetables of the cabbage family have been found to have a milder flavour when

cooked in an open pan with enough water to cover them than when cooked in a

tightly covered pan, a steamer or a pressure saucepan. A large amount of water

dilutes the natural flavour may be a matter of personal preference. The sharp

flavour of onions is reduced on cooking. Their flavour may also be milder and

sweeter or more concentrated if cooked in a large or small amount of water

respectively.

Changes in colour

          The green pigment, chlorophyll is so affected by both heat and acid that

marked change to a drab olivegreen colour may occur. This change is not

dependent upon the addition of acid because the natural acids occurring in plants

are sufficient to mar colour if heating is continued too long. Removing the cover

from the pan during the fruit few minutes of boiling should allow some volatile

acids to escape, decreasing the likelihood of their affecting the chlorophyll

adversely. All green vegetables, which included green beans, broccoli. Brussels

sprouts and cabbage showed considerable changes in colour with five minutes

overcooking in boiling water and with one minute over cooking in a pressure

sauce pan.

          In the presence of baking soda or other alkali, chlorophyll is changed to a

bright green, more water soluble pigment, chlorophyllin. The use of baking soda

in cooking green vegetables is not generally recommended.

          Not all anthocyanins as they occur in the plant behave in the same way

with changes of acidity and alkalinity. This may be owing to the admixture of

other pigments or to substances that modify the reactions.   

Effect of alkalis, acids and Cacl2 in cooking vegetables

          Sometimes sodium bicarbonate is added to some vegetables to help in

retaining the green colour and to hasten cooking. This method of cooking results

in heavy losses of many vitamins due to effect of alkaline pH and heat. When

vinegar, citric acid or tamarind fruit extract are added to vegetables before

cooking the vegetable does not cook readily and remains firm and hard. Calcium

chloride is used to increase the firmness of some foods during cooking.

Examples are canned potatoes and tomatoes and frozen apple slices used for

pies.  

FRUITS

Classification

1. Soft fruits - Goose berry, strawberry, blue berry

2. Hard fruits - Apples, pears

3. Stone fruits - Plums, peaches, cherries, apricots ,mango 

4. Citrus fruits - Oranges, lemon, sweet lime, grape fruit,

lime

5. Tropical fruits - Pineapple, melon, banana, guava, papaya,

sapota

6. Other fruits - Grapes, custard apple

 Composition

          Fruits contain a high range of water, ranging between 80-90 per cent. They

have only a small amount of protein and are also less in fat with a few exceptions

like avocado or butter fruit which contains upto 25% fat. The polysaccharide of

cellulose, hemicellulose and pectic substances are the structural components of

fruits. These make fruits important sources of roughage or bulk in the diet.

Various sugars viz., sucrose glucose and fructose are found in fruits, whose

content varies in different fruits. Fruits also contain some free organic acids.

Malic and citric acids occur in most of the fruits, but tartaric acid is a prominent

constituent of grapes. Oxalic acid, when present usually combines with calcium

to form calcium oxalate.

          Fruits are good sources of vitamin C. Some fruits are very valuable as

sources of ascorbic acid. Citrus fruits being excellent sources of this vitamin.

Straw berries, melons and tropical fruits are also good sources of ascorbic acid.

Yellow fruits contain caroteniod pigments which are precursors of vitamin A. The

B vitamins occur in  relatively low concentrations in fruits. Minerals are not

particularly high in fruits. However, sulphur phosphorus, iron and to a certain

extent, calcium are found in good many fresh fruits.

          Various pigments are present in fruits. The yellow and orange carotenoids

and the red, purple and blue anthocyarins, the green colour for chlorophyll and

light yellow anthoxanthins.

1. Chlorophyll– guava, gooseberry, country apple.

2. Carotenoids – mango, papaya, orange, watermelon  (lycospene), musk

melon    (-carotene), jack fruit, peaches (violaxanthin), tomatoes, grape

pink (lycopene, -carotene), pineapple (violaxanthin, -carotene).

3. Anthocyanins – grapes, blue berries, plums, cherries

4. Anthoxanthins – Guava, apple, goose berry, pears, custard apple,

banana.

Flavouring compounds of fruits are many and quite varied. The flavour

characteristic of a fruit, in many cases, is due to the characteristic blending of a

number of compounds. Acids contribute to the flavour of the fruits in the free or

combined form as salts and esters. Many aldehydes, ketones and esters

contribute to the flavour of fruits. Sugar and phenolic compounds present in fruits

also contribute to flavour. Some fruits contains essential oils which are also

important flavour contributors.

Pectic substances

     Pectins are complex colloidal substances formed by the combination of

large number of galacturonic acid. Pectic substances present in the form of

calcium pectate are responsible for the firmness of fruits. Pectin is the most

important constituent of jelly. It is commercial term for water – soluble pectinic

acid which under suitable conditions forms a gel with sugar and acid. In the

early stage of development of fruits, the pactic substances is a water-

insoluble protopectin which is converted into pectin by the enzyme

protopectinase during ripening of fruit. In over-ripe fruits, due to the presence

of pectic methyl esterase (PME) enzyme, the pectin gets largely converted to

pectic acid which is water – in soluble. This is one of the reasons that both

immature and over ripe fruits are not suitable for making jelly and only ripe

fruits are used. The pectin content of the fruit is tested by using alcohol test

(or) jelmeter test.

Fruits – use in cookery

1.     Fruits are used for the preparation of jam, jelly, marmalade,

preserves, candy, fruit juices, fruit bars and fruit toffees.

2.     Dried fruits, candies and preserves are used in the bakery and

confectionery products.

3.     Fruits are used in the preparation of puddings and ice creams.

4.     It adds variety to the diet.

5.     It is used as salad, refreshing and light dessert.

6.     Fruits and also used in the preparation of alcoholic beverages and

Vinegar.

7.     Fruits are used in the preparation of milk shakes and payasam

(Kheer).

Enzymatic browning

          Browning can be observed on the cut surfaces of light coloured fruits and

vegetables such as apples, banana, potatoes and brinjal due to enzymatic action

is known as enzymatic browning. Normally, the natural phenolic compounds

present in intact tissues do not come in contact with the phenol oxidase present

in some tissues. When the tissue is injured or cut and the cut surfaces is

exposed to air. Phenol oxidase enzymes released at the surface act on the

polyphenols present oxidizing them to Orthoquinones. The orthoquinones rapidly

polymerize to form brown pigments. Tyrosine, Chlorogenic acid, the various

catechins and several mono and dihydroxy phenols are among the many

compounds that can serve as substrates for oxidation by polyphenoloxidase to

cause browning or other discolouration in these foods.

Prevention of enzymatic browning 

          The methods commonly used for the prevention of enzymatic browning are

the following:

1.  Thermal in activation of polyphenolase: The most commonly used method

is blanching i.e. heating in live steam. The enzyme is fairly heat-stable and

requires to be heated at 100oC for 2 to 10 min. for complete inactivation. This

may not be possible in practice as cooking for long periods will affect the flavour

and texture of the fruit or vegetable. Further, blanching breaks the cellular

structure and brings about the contact of the enzyme with the substrate. If the

thermal destruction is not complete or rapid, the high temperature may

accelerate browning.

2.  Changes of pH using acids: The optimal pH for polyphenolase activity is

between 6.0 and 7.0. Lowering of the pH to 4.0 by the addition of citric acid

inhibits the phenolase activity. It is also possible citric acid reacts with the copper

present in the enzyme. Malic acid also has been found to be effective.

3.  Use of antioxidants: Ascorbic acid retards browning by virtue of its reducing

power. It reduces 0-quinones formed to the parent o-diphenols. Ascorbic acid is

used along with citric acid to prevent browning in fruit products. SO2, sulphites

and bisulphites inhibit effectively browning.

4.  Prevention of contact with oxygen: a)Using controlled / modified

atmosphere packaging for the processed foods i.e. packaging the product under

nitrogen prevents surface browning effectively. b)Contact with oxygen can be

reduced by immersing the fruits in water or liquids like milk, curd, fruit juice or

honey or sugar solution or sodium chloride solution after cutting or by covering

with a wet cloth.    

MEAT

Composition

          Meat contains 15-20% proteins of outstanding nutritive value. The lean

meat contains 20-22% proteins. Of the total nitrogen content of meat,

approximately 95% is protein and 5% is smaller peptides and amino acids. The

amino acid make up of meat proteins is very good for the maintenance and

growth of human tissue.

          The fat content of meat varies from 5-40% with the type, breed, feed and

age of the animal. When the animal is well-fed, fat deposits subcutaneously as a

protective layer around the organs. Then it accumulates around and between

muscles. Finally, fat penetrates between the muscle fibre bundles and this is

known as “marbling”. Marbling is desirable with some meats because the amount

of fat, and consequently the water holding capacity of the meat, gently influences

juiciness.

          Meat fats are rich in saturated fatty acids and it is likely that it produces

certain forms of atheriosclerosis. The cholesterol content of meat is about 75 mg

for 100 gm. The lean (protein) portion of meat contains greater proportions of

phospholipids (0.5 –1.0%) and these are located in the membranes of the cell.

The fatty acids in the lean portion of meat have a higher proportion of

unsaturated fatty acids than tissue fats. Carbohydrates are found only in very

small quantities in meat. Two carbohydrates found in meat are glycogen and

glucose.

          Meat is an excellent source of some of the vitamins of the B complex and a

good source of iron and phosphorous. Meat also contains sodium and

potassium. The vitamins and minerals are found in the lean portion of the meat.

          Meat contains the protein hydrolysing enzymes. Cathepsins and these are

responsible for the increased tenderness of meat during ageing.

          The colour of meat is due primarily to myoglobin. Variations in colour of

meat depend upon the chemical state of myoglobin. Meats cured with nitrates

remain pink as nitric oxide myoglobin is stable. Haemoglobin also contributes to

the colour of meat to some extent.

Post-mortem changes in meat

          The changes taking place in meat after slaughter may be grouped under

two heads: (1) onset of rigor mortis and (2) Development of tenderness in

muscle.

Onset of rigor mortis

          Just before an animal is slaughtered the muscles are soft and pliable. But

immediately upon death, as metabolism in the cells is interrupted processes

begin that lead to a stiffening of the carcass is known as rigor mortis. It is 24-48

hours in beef.

          Muscle is a highly specialized tissue; it converts chemical energy to

mechanical energy. Muscle requires a large outlay of energy for the contractile

apparatus and this energy is derived from ATP. For long-term activity, ATP is

derived by the oxidation of carbohydrates and lipids. When muscle is under

heavy stress and the oxygen available not sufficient, the anaerobic glycolysis

system becomes predominent. In glycolysis, glycogen is converted into pyruvate

and this is then reduced to lactate, under usual conditions lactate enters the liver,

where it is converted into glucose. The glucose is then carried back to muscle,

where eventually glycogen is resynthesized.

          When the animal dies, the circulatory system ceases to work resulting in

lack of oxygen. Due to glycolysis in postmorterm muscle, there is an

accumulation of certain waste products, especially lactic acid. Also, the ATP

concentration decreases and is lost in 24 hours or less.

          The increase in lactic acid concentration results in decrease in pH of

postmortem muscle. Also, in the absence of ATP, there is a formation of

permanent links between actin and myosin, i.e., the actin and myosin bridges

remain permanently fixed. The muscle passes into a state known as rigor mortis

(stiffness of death). These postmortem effects brings about changes in the

quality attributes of meat, such as texture and water-holding capacity, colour and

flavour. Nutritional quality, however is not much affected.

Tenderisation of meat   

          Tenderness is the most desired characteristic in meat. The amount and

distribution of connective tissues and the size of the both muscle fibres and

bundles of fibres determine the tenderness of meat. The number and strength of

cross linkages between the peptide (bonds) chains of collagen increase with the

age of the animal and this decreases the amount of the collagen that may be

solubilised during cooking thus contributing to decreased tenderness. There are

different methods of tenderizing meat.

1.      Cold room storage results in the ripening of meat with tenderizing from the

meat’s natural enzymes.

2.      The mechanical methods of tenderizing meats include pounding, cutting,

grinding, needling, or pinning and the use of ultrasonic vibrations. Mechanical

methods cut or break the muscle fibres and connective tissues.

3.      The art of using enzymes for tenderizing meat is an old one. Wrapping of

meat in papaya leaves before cooking results in tenderisation. This is the

result of the action of the enzyme papain on meat proteins. Other enzymes

used for meat tenderisation are bromelain from pineapple, ficin from figs,

trypsin from pancreas and fungal enzymes. These proteolytic enzymes

catalyse the hydrolysis of one or more meat proteins. The enzymes also

hydrolyze the elastin of the connective tissues. To achieve uniform

tenderness, papain is injected into the veins of animals some 10 minutes

before their slaughter. Tenderising enzymes     remain active until the meat is

heated. Papain is active at 55 C.

4.      Meat may be tenderized by the use of low levels of salts. Salts increase the

water holding capacity of muscle fibres resulting in tenderness and juiciness.

Salt also solubilises the meat proteins. Tenderness of meat is improved when

freezer dried meat is rehydrated in a weak salt solution instead of water. Salts

used for tenderisation are NaCl, sodiumbicarbonate and sodium and

potassium phosphate.

5.      Another method of increasing tenderness in meat is by change of pH.

Decreasing or increasing the pH of meat increases hydration and to its

tenderness. Soaking beef for 48 hours in concentrated vinegar increases its

tenderness and juiciness.

6.      Exercised animals give tender meat.

Factors affecting the tenderness of meat

          The factors affecting the tenderness of meat are (1) The fat content of

meat (2) The connective tissue content (3) Age of the animal (4) The texture of

muscle fibres and (5) Conditioning of meat after slaughter.

1.  Fat content and toughness of meat: Some workers have reported that fat

content of meat is well correlated with tenderness. Several others have found no

correlation between fat content and tenderness of meat.

2.  Connective tissue:  Studies carried out by many workers have shown that

there is no correlation between connective tissue content and tenderness of

meat. The meat of older animals are tougher than that of the younger animals

eventhough the collagen contents of younger animals are more than those of

older animals.

3.  Texture of meat and tenderness:  Broady found that tenderness depends

on texture of meat. The number of fibres in a bundle is a measure of texture; the

greater the number of fibres in a bundle, the finer is the texture; the finer the

texture, the tenderer is the meat.

4. Conditioning of meat after slaughter :  If the meat is kept in cold store at

0oC for 48 hours, the muscle tissue is acted upon by the proteolytic enzyme

cathepsin found in muscle and the meat becomes tender.

5. Age of the animal : Meat from older animals is tougher than meat from

younger animals. At the same time, the collagen and elastin contents of meat of

older animals have been fond to be less than those of young ones.

Meat cookery

Methods / Types of cooking meat

Dry heat

1.  Roasting :  The meat is placed uncovered in a rack in a shallow pan to keep

the meat out of drippings. The roasting pan is placed in the centre of the oven

temperature of 163oC is maintained by thermometer. This ensures the adequate

browning of meat for good flavours and good appearance. For small roasts an

oven temperature of 177oC is used. Roasting continue to cook at the centre even

after they are removed from the outer surface. If meat is covered, the steam from

the roasting meat is tapped inside and meat gets cooked by moist heat cookery.

2.  Broiling:  It consists of cooking meat by direct radiant heat such as the open

fire of a gas flame, live coals or electric oven. Broiling is applied to tender cuts

that are at least 2.5 cm thick. Thinner cuts will be too dry if broiled.

          To broil, meat is placed on a rack is adjusted in  such a way  that the top of

the meat is some 5 to 10 cm from source of heat. A tray should be placed

beneath the meat rack to collect the melted fat. Broiling is carried out at a

temperature of 176oC until the top side is down. The broiled side is salted and

turned and broiled on the other side. Broiling is faster method of cooking meat by

dry heat than roasting. But roasting produces more juicy and tender meats than

broiled meats.

Pan Broiling:  Meat is placed in a cold girdle and heated so that meat cooks

slowly. Any fat that accumulates in the pan is removed so that the meat will

continue to pan broil rather than pan fry.

Frying:  Two methods of frying are pan-frying and deep fat frying. The

temperature is to be controlled such that the meat does not develop a burned

flaovur and dryness. With high temperature fat decomposes to acrolein, which

impairs the flavour of meat. Too high temperature results in inside uncooked and

too low temperature results in greasier product.

Moist heat

Braising:  In this method of cooking, the meat is first carefully browned on all

sides by broiling, pan broiling or frying. Then it is cooked with or without the

addition of water of the meat. Tomatoes and fruit juices may be added as liquids.

The juices not only furnish liquid for softening the collagen but also afford a

variety of flavours and may hydrolyse protein because of their acidity.

Stewing:  Large pieces or tough meat are cooked in sufficient water until tender.

Pressure cooking:  Braising and simmering of meat takes a long time for

cooking. This method take less time. Pressure cooked meats are less juicy and

cooking losses are great.

Changes during cooking

1.     Cooking destroys the microorganisms that may have contaminated meat.

Live trichinae are quickly destroyed by heating the meat to 55oC.

2.     Cooking brings about changes in the colour of the meat, when fresh meat is

cooked its protein pigments are denatured. Denaturation of the protein

caused rapid release of the haem pigments from the globin part of the

molecule and the free haem is very sensitive to oxidation. On heating red

meat generally turns brown due to the oxidized pigments in meat. This

change in colour is used as an index of cooked meat. Meat cooked to rare

condition has less of oxymyoglobin denatured and more brown. Meats cured

with  nitrate retain red throughout cooking.

3.     Heat treatment brings about the denaturation of most other proteins. The

enzymes are inactivated. The contractile proteins become dougher. Ideal

cooking methods for meat should minimize the hardening of contractile

protein and maximize the softening of the connective tissues. Cooking

temperature and time should be adjusted so that the tenderizing effect due to

the conversion of collagen to gelatin is not offset by the increasing toughness

owing to an excessive coagulation of contractile protein.

4.     Flavour compounds are produced or changed on heating. Proteins and free

acids of meat on heating produce some volatile break down products. These

include sulphur containing compounds, aldehydes, ketones, alcohols, amines

and others. Lipid components also break down into various volatile

compounds. These volatile compounds in both fat and lean protions of meat

contribute to the flavour and odour of the cooked meat.

5.     During heating, meat fat melts, adipose tissue cells are ruptured and there

is a redistribution of fat. Some fat is disposed finely in locations where

collagen has been hydrolysed. When meat is eaten warm, the melted fat

serves to increase the palatability of the product by giving a desirable mouth

feel.

6.     Meat contains a high percentage of water. Only a small percentage of this

water is bound very closely to the proteins, muscle tissue and the rest exists

as free molecules within the muscle fibres and connective tissues. Heating

reduces the water holding power of meat which is related to its juiciness. The

loss of water on cooking does not bring about changes in the nutritive value of

proteins and done stages are more juicy than well done meats.

7.     Nutritive value of cooked meat generally remains high. Normal cooking does

not bring about changes in the nutritive value of proteins and minerals are not

lost by heat. Some minerals may be lost in meat drippings but on the other

hand, cooking dissolves some calcium from bone and so enriches the meat in

this mineral. There is loss of some B vitamins during cooking. But most of the

cooked meat retains more than 50% of the B vitamin present in the uncooked

meats.

Factors affecting cooking quality

1.     Types and treatment of the live animal.

2.     Slaughtering and carcass characteristics the various muscles of the

carcass.

3.     The composition, structure and function of the muscles.

4.     Post-mortem changes.

5.     Cooking methods

6.     Processing treatments. 

    

Egg

Structure

 

          A fully formed egg has a shell, two membranes, albumen (or) white of the

egg, yolk (or) the yellow of the egg and germinal disc. The various elements are

arranged with great precision and their total organizations is essential to the

specific function of each part.

Shell: The shell of the egg is made of calcium carbonate (calcite) deposited in an

organic matrix and it forms the protective covering of the inner contents of the

egg, along with the two membranes. The matrix fibres have significant influence

on shell strength and pass through calcite instead of surrounding it. The matrices

are made up of protein-polysaccharide complexes. An egg shell is brittle and

easily breaks. It is porous and contains thousands of small holes (7,000-17,000

per egg) which allows gases to pass in and out of the egg for the developing

embryo, in the case of fertilized egg. The small holes are covered with a thin

layer of a gelatinous material (mucoprotein) called the cuticle or bloom. The

cuticle seals off the pores of the shell to some extent and helps avoid an

excessive evaporation from the inner contents of the egg. It also restricts the

entry of microorganisms into the egg and thus protects its inner contents from

various infections. The cuticle is soluble in water and easily removed by washing

which results in hastening the deterioration of egg quality.

The shells of some eggs are white while those of others are brown. The

pigmentation of the shell depends on the breed of the hen and has no bearing

on the quality of the egg, though eggs with white shells are preferred. Eggs

also show great variety in the surface characteristics of their shells. Some are

glossy, others dull, some smooth and some rough.

Shell membrane:  Within the shell are an inner and outer membrane that also

protect the quality of the egg. Both the membranes are porous and composed of

fibres. The outer membrane which is thicker than the inner one is firmly attached

to the shell. The outer membrane was six layers of fibres, whereas the inner has

three. The inner membrane is attached to the outer and the two membranes are

loosely attached to one place, usually at the broad end of the egg. The

membranes are composed of protein-polysaccharide.

          The eggs contain little or no air-cells when it is laid. After being laid,

because of the lower temperature of the outer surrounding of the egg than when

it was in the hen’s body, there is a contraction of the inner contents of the egg.

This results in air being drawn into the shell resulting in a small air-cell formation

between the shell membranes usually at the large end of the egg.

Egg white:  The white of the egg consists of three layers: two areas of thin white

encompassing one area of thick white. The yolk is enclosed in a sac called the

‘vitelline membrane’. Immediately beyond this is another membranous layer

known as the chalaziferous layer. The yolk is connected to thick or firm albumen

by two twisted rope like extensions of the chalaziferous layer called chalazae.

The chalazae strive to another the yolk in the white and keep in centered in the

egg.

Egg yolk:  The yolk carries the indistinct germinal disc or germ spot which, under

suitable conditions, develops into a chick. Beneath the germ spot extends a white

column called the latebra. The yolk itself is layered into sections of white and

yellow yolk, but these are not readily discernible.

          The yolk of the egg is enclosed in a sac called the vitelline membrane.

Immediately adjacent to the vitelline membrane, the thin membrane that

surrounds the egg yolk, is chalaziferous or inner layer of firm white. This

chalaziferous layer gives strength of the vitelline membrane and extends into the

chalazae. The chalazae appears as two small twisted ropes of thickened white,

one on each end of the yolk and anchor the yolks in the centre of the egg.

Chalazae appear to have almost the same molecular structure of ovomucin.

Composition

          The distribution of weight of egg is shell 8-11%, white – 56-61%, yolk 27-

32%. The egg shell is primarily calcium carbonate deposited in an organic matrix.

This is          in edible portion of the egg. The composition of egg shell is calcium

carbonate-93.07%, magnesium carbonate -1.39%, phosphorus pentoxide -

0.76%, organic matter 4.15% (Matrix protein and polysaccharide).

          The composition of egg white and yolk differ considerably. The lipid

content of albumin is negligible when compared to yolk. A very small amount of

glucose is present in the egg white. The percentage composition of egg white is

water -88.0%,              protein -11.0%, fat -0.2%, minerals -0.8% and the

percentage composition of egg yolkis water -48.0%, protein -17.5%, fat -32.5%

and minerals -2.0%.

          The egg white consists the proteins namely ovalbumin, conalbumin,

ovamucoid, ovomucin, lysozyme, Avidin, ovoglobulin and ovoinhibitor.

          The egg yolk contains lipovitellins, phosvitin, livetin and low density

lipoprotein fractions. The egg yolk contains triglycerides, phospholipids and

lipoproteins.

          The colour of the egg yolk varies from a pale yellow to brilliant orange

depending on the amount and type of pigment present in the diet of the hen. The

colour is due to the presence of carotenoids and xanthophylls. Of these, the

caroteniods are converted into vitamin A in the body. Mostly, deep coloured yolks

are rich in vitamin A content. Xanthophylls are responsible for the yellow colour

and they are not converted into  vitamin A.

          Calcium which is the most abundant mineral in egg, is mostly concentrated

in the shell. It is also present in a significant amount in yolk and in a small

amount in egg white. Phosphorus is the most abundant mineral in the yolk. Eggs

are an important source of easily assimilable iron. In addition to these, other

mineral present in egg white and yolk in varying amounts are sodium, potassium,

magnesium, sulphur and chlorine. The mineral content of the egg depends upon

their concentration in the hen’s diet.

Egg quality     

       Egg is an excellent food for man and, as such, its quality is of very great

importance. If proper care is not taken, the quality of the egg deteriorates rapidly

and its food value is adversely affected. A number of factors constitute egg

quality including both external and internal factors. External factors include the

size and shape of the egg and condition of the shell. Internal factors determining

the quality are the size of the air-cell and condition of the albumen, yolk and the

germ spot.

          The size of an egg is indicated by the weight of the newly laid eggs. Hens

lay eggs of different sizes, varying from 49 to 70 gm. The size of the egg

depends upon the hen’s inheritance, body size, stage of laying, season of laying,

age, diet and health of the bird. The indigenous Indian hens, however, usually lay

eggs weighing less than 45 gm. The size dose not reflect the quality and

similarly, the grade of the egg does not give an indication of its size. A point in

favour of small eggs is that they contain a relatively higher proportion of yolk than

large eggs.

          Though the shell of an egg is not consumed, its condition is important

because of the protection if gives to the edible portion. The factors affecting the

condition of the shell are its strength, porosity, soundness, texture, colour and

cleanliness. The strength of the shell depends upon its thickness which in turn

depends upon the nutrition of the bird and other factors. A high porosity of the

egg shell will hasten the deterioration in the quality of egg contents, as it permits

the evaporation of moisture and allows dissolved CO2 to escape from the inner

contents during the storage of egg. A porous shell is graded lower than a shell

with fine pores. The texture of the egg shell varies. This does not materially affect

the quality of the inner contents. However, there should not be ridges or grooves

spread over a large area of the shell. The colour of the shell varies but has

nothing to do with the quality of the edible portion of the egg. Finally, eggs must

be clean. Any dirt on the egg shell means the presence of a large number of

contaminating microorganisms. Eggs may be dry cleaned or wiped with a piece

of moist cloth if they are slightly soiled or washed with warm water of a

temperature of about 10oC higher than that of the egg.

          The quality of the internal contents of the egg is determined by the size of

the air cell, the denseness of the egg white and the size, distinctness, colour and

mobility of the yolk. As the quality of the egg deteriorates, the size of the air-cell

increases and the white becomes thinner. The yolk should be centred in the egg

and its position tends to drift of centre when the egg becomes stale. Since yolk

colour depends largely on the colour of the chicken feed, the colour is not an

indication of the quality of the egg, though eggs with darker yolks are preferred.

The yolk should be free from abnormalities, which include blood spots,

embryonic development, mold growth, discolourations and other signs of

spoilage.

Evaluation of egg quality

          The quality of egg in the shell is evaluated most commonly by a process

known as candling. The egg is held upto a light source in a dark room and is

viewed in silhouette while being rotated. Candling will reveal a crack in the shell,

the size of the air cell, the firmness of albumen, the position and mobility of yolk

and the possible presence of foreign substances. Sometimes the quality of egg is

determined by dropping the egg in water. If the egg sinks it is considered good,

while it is considered to be of poor quality of it floats. This is not only an effective

method for finding out the egg quality, it only gives a rough idea. It shows that the

egg floating on water has lost in weight due to dehydration.

          The quality of an egg can be graded by breaking the egg out of the shell.

The appearance of the shelled egg is an excellent indication of freshness. Fresh

egg have a high yolk rather than a flat yolk, i.e. the yolk index, a figure derived by

dividing the height of the yolk by its diameter, is high in fresh eggs. Also, the

height of the thick albumen (albumen index) indicates the quality of egg i.e. fresh

eggs have a larger amounts of thick white relative to runny thin white. This

causes a stale egg to spread out over a larger area than a fresh egg.

Egg grading

             Eggs whose quality has been determined are graded for marketing purposes.

They are graded according to size and quality which are independent of each other. In

India, eggs, are graded according to weight into four grades.

Grade Weight of individual egg (g)

Extra large> 60

Large53-59

Medium 45-52

Small 38- 44

          Grading according to size helps the buyer obtain a particular quantity of

the food material for a given price.

          Clean eggs with unbroken shell are graded on quality depending upon the

depth of air-cell, centering of egg yolk and freedom from defects, as grade A and

B in India. These are further subdivided based on size. In the US, eggs are

classified into three groups as AA, A and B.

Egg cookery

Effect of heat on egg proteins (changes on cooking)

          An egg finds numerous uses in food preparations because of its

fundamental properties, which in turn, depend on the proteins of the egg.

Coagulation of egg proteins is valuable in many different cooking processes. Use

of egg as a thickening agent, binding agent and clarifying agent are all based on

the coagulation of its proteins when heated.

          Various proteins coagulate at different temperatures. The coagulation of

the undiluted proteins of an egg depends on the combinations of proteins

present. Egg-white proteins begin to coagulate at 52oC if the heating conditions

are controlled carefully. when the white is heated more rapidly coagulation

begins at 60oC and is completed at 65oC. The coagulation of egg-yolk begins at

65oC and is completed at 70oC.

          The rate and extent of coagulation depend also on time and added

ingredients. A rapidly heated egg mixture coagulates at a higher temperature

than a slowly heated one. The egg-white coagulated at a high temperature is firm

and tough when compared with the soft and tender product obtained when

coagulation takes place at a lower temperature. A slow rate of heating and

consequently, a lower coagulation temperature is preferable in food preparations.

          Ingredients added to eggs affect the temperature of coagulation of egg

proteins. Dilution by the addition of water or milk raises the temperature of

coagulation. Sugar in an egg mixture also elevates the coagulation temperature.

Acids, such as cream of tartar or lemon juice, reduce the coagulation

temperature by helping reduce the pH of the egg mixture to the isoelectric point.

The presence of salt lowers the temperature of coagulation. Salt causes

coagulation to occur because the charges of the ions neutralize the charges on

the protein molecule. The presence of salt, thus, aids the coagulation of a dilute

egg mixture.

Role of egg in cookery

1.     Eggs are used as boiled, scrambled, or poached for table use.

2.     Used as a thickening agent – stirred custards and baked custards,

soups, puddings. Help in gel formation.

3.     Emulsifying agent-mayonnaise, ice cream.

4.     Leavening agent- cakes, foamy omelette, soufflés, meringue. All egg

white foam used in certain candies also improves the texture by controlling

crystallization of sugar.

5.     Binding and coating agent- cutlet, french toast or Bombay toast, banana

fritters.

6.      Interfering substances – ice creams. Beaten egg which act as interfering

substances in frozen desserts. Tiny bubbles of air trapped in egg prevent

ice crystals from coming together and creating large masses of icy

material.

7.     Clarifying agent – Raw eggs can be added to hot broths and coffee.

When protein in egg coagulates they trap the loose particles in liquid and

clarify it.

8.     Garnishing agent – Hard boiled eggs are often diced and used to garnish

dishes.

9.      Flavouring agent – custards.

10.                        Enriching agent – To enrich the nutritive value e.g. cake.

11.                        Glazing agent – for pastries of all types to give the surface

a golden brown colour when cooked.

12.                        Improves colour.

Methods of egg cookery :

          Egg may be cooked without the addition of any ingredients or they may be

included in recipes. The basic methods of preparing egg products include those

prepared in the shell and out of the shell.

a.  Eggs prepared in the shell : Soft cooked and hard cooked eggs are those

prepared in the shell. The criteria for a soft- cooked egg are that the white should

be firm but tender and the yolk a thick liquid. In hard-cooked (hard-boiled) eggs,

the white becomes an opaque tender gel and the yolk is completely coagulated.

For good results, eggs are placed in boiling water (sufficient water should be

used to cover the eggs) and then a simmering temperature is maintained. Eggs

should be simmered for 3-5 min. for soft cooked eggs and for 15-20 min. for hard

cooked eggs. To prevent the cracking of the shell during cooking, the egg may

be lifted quickly in and out of simmering water a couple of times.

          Sometimes, with hard –cooked eggs, a greenish - grey layer is obtained at

the interface of the yolk and egg white. This is due to the ferrous sulphide formed

by the union of iron of the yolk and hydrogen sulphide liberated from sulphur in

the white. Ferrous sulphide is formed as the pH of the yolk increases. Prolonged

heating or a slow rate of heating will increase the formation of ferrous sulphide.

By using fresh eggs, carefully controlling the simmering temperature and rapidly

cooling the hot eggs in cold water, the formation of ferrous sulphide can be

significantly reduced.

b.  Eggs prepared out of the shell- Poached egg:        A poached egg is

prepared by sliding the contents of a good quality egg carefully into a pan of

water heated to simmering temperature. Use of simmering water in preference to

boiling water is important as in the former case, the egg proteins will be more

tender and the egg will hold its shape better. Use of egg poacher with individual

cups for each egg will eliminate the spreading of egg-white. When the white is

coagulated completely the egg should be removed from water quickly. In a well

prepared poached egg the white should be uniformly coagulated in a single

mass, without spreading extensively and the yolk should be thickened, being

covered by a thick coating of white. No part of the yolk should be coagulated to

the point where it begins to solidify.

Fried egg: The egg is fried in just enough fat to prevent it sticking to the pan.

The pan should be sufficiently hot to coagulate the egg white but not sufficiently

hot to toughen it or to decompose the fat. The egg may be turned over or a small

amount of water may be added and a lid placed on the pan so that the steam

may speed the cooking of the upper surface. Cooking may also be speeded up

by basting the top of the egg with hot fat. The white of the fried egg should be

thick and compact. It should be uniformly coagulated and tender. The yolk should

be unbroken and covered with a layer of coagulated white.

Scrambled egg: For scrambled egg, the yolk and white are blended until an

uniform mixture is formed. A small amount (one teaspoon per egg) of milk, cream

or water may be added to the mix along with salt and seasonings. The mix is

then heated slowly and the egg is scraped, as it coagulates. This helps the

making of scrambled egg which is moist, tender and fluffy. Further heating results

in a product which is shrunken, tough and dry. Good quality scrambled eggs are

obtained by cooking in a double boiler.

French omelet: A french omelet or plain omelet is prepared by beating the

whole egg, with or without a small amount of liquid and flavouring material. The

mixture is then cooked in a greased pan until it is coagulated. Cooking is aided

by covering the pan with a lid during part of the cooking period. The omelet is

then folded or rolled. Different varieties of omelet can be prepared by the use of

fillings and sauces.

c. Products based on egg as a thickening agent   

          As egg proteins coagulate in a product, the entire product becomes more

viscous. This thickening property of egg is made use of in a number of products,

such as custards and cream pie fillings. Proper control of coagulation

temperature determines the quality of the product.

          Custards are of two types : 1.  The soft custard or stirred custard which

gives a product of creamy consistency by being stirred while it is cooked, and 2. 

Baked custard which is allowed to coagulate without stirring.

 

Stirred custard: The ingredients in custard are eggs, sugar, milk, salt and

flavourings. The egg is blended and strained. Then milk and sugar are added

and stirred. The milk used is generally scalded to approximately 85oC as it

shortens the cooking time and improves the flavour and texture of the product.

The custard mixture is heated over hot water, water being just below the boiling

point, for the entire heating period. A slow rate of heating is essential for the

preparation of a smooth viscous stirred custard. The custard is stirred

continuously as it is being cooked. Stirring breaks up the gel as it is formed.

When the custard reaches the desired thickness it coats a spoon evenly. Then it

is poured immediately into a shallow dish placed in cold water or ice water so

that the custard is cooled rapidly. Excessive coagulation results in curdling.

          A stirred custard should have the viscosity of a heavy cream and be very

smooth with no suggestion of curdling. Custard is a nutritious and pleasing

dessert sauce served other cakes, fruits or various baked desserts.

Baked custard: A baked custard is made from the same recipe used for stirred

custard. The stirred homogenous mixture of custard ingredients is placed in a

pan of hot water in a oven at 177oC. The water acts as an insulator to slow the

rate of heat penetration to keep the outside of the custard from being over baked

before the interior is set. Baked custard should be removed from the oven when

a knife inserted half-way between the edge and centre comes out clean. An

overheated baked custard becomes porous, the pores filled with watery serum.

          A baked custard should be firm, yet tender and the texture should be

smooth and uniform and without porosity, when cut no syneresis should be

apparent and the colour should be uniform with no flecks of yellow or white. The

filling for a custard pie is baked custard.

Cream pudding and pies: The term cream pudding is misleading since it is egg

yolk that is added to corn starch pudding rather than cream. The preparation of

these products is based on the ability of egg to bind the ingredients.

          In the preparation of cream puddings and pie fillings, the starch, sugar, salt

and water are boiled together until they become thick. The mixture is removed

from the heat and some of it stirred carefully into beaten egg-yolk. Then the yolk

mixture is blended with starch mixture and the pudding is heated over simmering

water until the protein coagulates. Slow stirring is needed during this period to

promote the uniform coagulation of yolk and avoid lumps.

          Cream pudding and pie fillings should be smooth and feel light on the

tongue, without gumminess or stickiness. When cut, the pie filling should soften

slightly but not actually flow.

d. Egg foam products – Meringues : Meringues are egg white foams into which

some acid and sugar are incorporated. There are two kinds of meringues – soft

and hard. Soft ones are used as toppings for cream pies and hard meringues as

confections in combination with fruits, ice creams or syrups.

          Soft meringues are prepared by beating the egg-white to the foamy stage.

Then, about 25 gm of sugar per egg-white are added gradually and beaten until

the peaks just bend over. The fine-structured meringue is spread on soft pie

fillings. For maximum volume and minimum drainage, the meringue should be

placed immediately on a warm filling, the edges should be carefully sealed, and

then baked in a pre-heated oven. This coagulates the protein and stabilizes the

foam without causing undue shrinkage.

          Usually, soft meringues are baked at 177oC. A meringue is done when a

pleasing medium brown colour develops on the ridges. If the meringue is under

baked, the structure is not set and results in “weeping” i.e. the foam breaks down

and leaks into the surface of the filling. If over baked, the surface is tough and

amber coloured droplets of syrup appear on the surface of the baked meringue.

A soft meringue should be fluffy, slightly moist and tender. The surface should be

fine grained, glossy and light brown in colour.

          Hard meringues contain twice as much sugar as soft ones. As a large

amount of sugar delays foam formation, the first half of sugar is gradually added

to form soft meringue. A soft meringue should be fluffy, slightly moist and tender.

The surface should be fine grained, glossy and light brown in colour.

          Hard meringues contain twice as much sugar as soft ones. As a large

amount of sugar delays foam formation, the first half of sugar is gradually added

to form soft meringue. Then the other half is slowly added and beaten till the

desired stiffness of peak is obtained. Hard meringues are baked at a lower

temperature and for a longer time than the soft variety. Hard meringues should

be dry, crisp and tender. They should have a delicate colour and look fluffy.

Fluffy omelets: Fluffy omelets are prepared by beating egg-white and yolk

separately and folding them together, and then baking. The egg white is beaten

until the peaks just bend over. If a liquid is added it is gradually added to the

white. Without delay, the beaten egg-yolk is folded into beaten white until the

mixture is homogenous and cooked promptly as in the case of plain omelet. A

fluffy omelet should be light, tender, delicately brown and cooked uniformly

throughout.

Soufflés: Souffles are similar to fluffy omelets. They differ from the latter in that

they contain white sauce. They may also contain other flavouring ingredients,

such as grated cheese, meats, poultry, fish, pureed vegetables etc. In soufflé

preparation, yolks are added to a thick white sauce which is warm. The egg-

whites are beaten to form stiff peaks. Then the sauce containing the yolk is

folded into the white foam until no streaks show. The mix is immediately baked in

a pre-heated oven at about 175oC. Souffles should be light, tender, flavourful and

pleasing brown with no layers at the bottom.

Foam cakes:        The foam of egg-white is important in making foam cakes like

angel, chiffon and sponge cakes. Their volume and structure depend on the use

of egg-white foams.

e.  Products based on egg as emulsifying agent:        Egg yolk is a good

emulsifying agent. Yolk itself is an emulsion and thus partly explains its

outstanding emulsifying properties. Salad dressings are emulsions of oil-in water,

in which droplets of oil are suspended in an aqueous medium. This emulsion is to

be stabilized in the preparations of salad dressing. Whole egg or egg yolk is

frequently employed to stabilize emulsions. Various baked products, such as

cheese soufflés, cream puffs and shortened cakes also rely on egg as an

emulsifier.    

     

FISH

Classification of fish

          Edible fish are categorized as either fin fish or shell fish. The term fin fish

refers to the fishes that have bony skeleton. Shell fish is used to designated both

mollusks and crustaceans. Most fin fish come from salt water, however, great

lakes and inland water add considerable amounts to the total catch. Edible shell

fish are mainly salt water fish.  

Composition

          Fish is an excellent source of protein due to its quality and quantity. They

contain around 20% protein. The biological value of fish protein is 80%, that is it

has good quality protein compared to any other animal proteins. Fishes are not

good sources of energy because they are not good sources of carbohydrate and

fat. Fish contains less amount of fat compared to meat and poultry. The lipid

content of both fish and prawns is very low and varied within a very narrow range

of 1-28%.

          Fresh water fish contains n-3 poly unsaturated fatty acids. The levels of

these fatty acids varied widely from 0.07 to 0.28 g/100g edible muscle, most of

which was made of eicosapentaenoic acid and decosahexaenonic acid.

Commonly consumed fish murrel has the highest content of n-3

PUFA-0.28g/100g edible muscle. These values are similar to those of marine fish

and indicate that both are good sources of n-3 PUFA. Fresh water fish with fat

content of about 1-7% contains n-3 PUFA of about 0.26/100g edible muscle,

whereas in marine fish with similar fat content (1.8%) the  n-3 PUFA content is

0.39g/100g edible muscle. Thus marine fish is relatively rich in n-3 fatty acids. In

prawns the n-3 PUFA ranged from 0.2-0.3 g/100g edible muscle with total fat

content of 1.0-1.8%.

          Fish is rich in calcium particularly small fish when eaten with bones. Marine

fish or ocean fish are good sources of iodine. Oysters are good sources of

copper and iron.Sodium content of fresh water fish is slightly less than meat.

          Fish liver oils are excellent sources of fat soluble vitamins. Rohu contains

vitamin C. Fish are good sources of niacin and vitamin D.

Characteristics of fresh fish

1.       The skin looks bright and shiny. The skin on stale fish may show signs

of wrinkling and shrinking away from the flesh.

2.       The eyes of a freshly caught fish will be convex, the pupil black and the

cornea translucent. The eyes should be bright, clear and bulging.

3.       The gills of freshly caught fish are bright red, but as the blood in them

oxidizes they rapidly turn brownish and any mucus on them turns opaque.

4.       If fish is split along the back bone and try lift out the bone, it should

stick firmly to the flesh. If the bones lifts out easily, the fish is stale.

5.       The surface should be free of dirt and slime.

6.       The flesh should be firm to touch with no traces of browning or drying

around the edges.

7.       A fish having odour indicates deterioration due to oxidation of

polyunsaturated fat and bacterial growth. Rancidity is revealed by

yellowish spots on the surface. Rancidity can be recognized by sour taste,

uncharacteristic of fresh fish.

Spoilage

          Fish is considered in prime condition for upto three hours from catch, in

average condition from three to six hours and on the way to spoilage from the

sixth hour.

Microbiological

          While live fish is bacterioligically sterile, there are large number of bacteria

on the surface slime and digestive tracts of living fish. When fish is killed, these

bacteria multiply rapidly and attach all tissues. Growth of microorganisms and

enzymes affect of the quality.

Physiological

            Fish struggle when caught and hence all the glycogen stores in the

muscle and liver are used up. There is no glycogen left for being converted into

lactic acid which helps to increase the pH of the tissues and retard the

multiplication of microorganisms.

Biochemical

          The important biochemical change leading to the development of the

characteristics fishy off odour is due to the production of trimethylamine by the

action of bacterial enzymes on phospholipids and choline present in fish. The fats

present in fish are highly unsaturated. By the action of bacterial lipases and

lipoxidases, free fatty acids are produced  and the fat undergoes oxidative

rancidity.

Cooking of fish

Principles of cooking fish:  Since fish has little connective tissue, it requires a

much shorter cooking time than meat and poultry. Fish should be cooked at

moderate temperatures long enough for its delicate flavour to develop, for protein

to coagulate and for very small amount of connective tissue present to

breakdown. The flesh of fish is sufficiently cooked when it falls easily into clamps

of snowy white flakes when tested with a fork. Cooking fish at high temperature

or cooking it too long, causes the muscle protein to shrink leaving the fish tough,

dry and lacking in flavour. Fish can also be cooked by coagulating proteins with

acids such as lemon or lime juice.

Methods of cooking fish

          Fish is usually cooked by dry-heat-broiling, baking and frying. Moist heat is

also effectively employed to protect the delicate flavour of the fish. Fish such as

salmon, mackerel and herring contain some fat and require, very little addition of

fat in cooking. Some fish like cod, haddock, halibut and bass, contain very little

fat and required added fat during cooking. Fin fish may be poached in water (or)

court bouillon, a highly seasoned stalk that enhances the flavour of fish. In order

to keep the fish from falling apart while it cooks it is best to tie the fish in cheese

cloth of parchment paper before immersing it into the hot water. Shell fish needs

only to be plunged into the simmering salt water but care must be taken to keep

the water from boiling so that the fish meat remains juicy and tender.

          Shell fish cooked in the shell is said to retain its flavour better. Fish that is

oven baked enclosed in a sort of oil paper is called “en pap illole”. The difference

in over temperatures do not affect the palatability. Fish can be baked with butter,

garlic and spices. Unlike meat and poultry cooked fish tends to break up easily

thus requiring careful handling during cooking and serving. To test  if fish is

cooked insert a fork into the fleshiest part of the fish. The flesh will flake away if

cooked. The flesh looses its translucency and becomes opaque.

          Some Indian recipes of fish are fish fry, kolambu, cutlet, puttu and crabs

with gravy.

POULTRY

Composition 

                           Poultry meat has a high   protein content varying from 18-25%,

and is comparable in quality and nutritive value to other meats. It contains all the

essential amino acids required for building body tissues. Thee is little fat on the

meat of young birds, but the fat content is influenced by age, and species of

poultry. In any case, the fat content of poultry is less than half that of other

meats. Chicken fat is more unsaturated than the fat of red meat and this has

nutritional advantages. Like other animal tissues, poultry flesh is a good source

of B vitamins and minerals. The dark meat of chicken is richer in riboflavin than

the light but the light meat is richer in niacin.

          Because of its high protein-to-fat ratio, poultry meat is advantageous to

persons who must restrict the intake of fats. The importance of poultry in a

country like ours with low nutritional standards cannot be over emphasized. Use

of poultry products in our diet will help avoid malnutrition. Another advantage of

poultry in our country is that it is eaten by persons who have objection to eat beef

or pork.

Method of cooking 

               Raw chicken has little or no flavour; it develops during cooking. The

principles of cooking poultry are basically the same as for cooking meats. The

cooking method is selected on the basis of the tenderness of the poultry and its

fat content, both influenced mainly by the age of the bird.  Moist heat methods

are applied to older and tougher birds in order to make them tender and

palatable. Dry heat methods are applied to young tender birds.

          The changes that take places during the cooking of poultry are similar to

those of other meats. To obtain tender, juicy and uniformly cooked poultry, low to

moderate heat is to be used. Intense heat results in the toughening of proteins,

shrinkage and loss of juiciness. 

Broiling and frying:  Young tender poultry is cooked by broiling, frying, baking

or roasting. For broiling, the bird is placed in the broiler with the skin side down.

The whole bird or halves may be broiled. The broiler is placed about 10 cm from

the flame or heating element and cooked at a broiling temperature of 177oC till

the internal temperature of the breast muscle reaches 95oC (about 45-60 min).

Because of the low fat content of the young birds, pasting with melted fat will

improve the flavour, palatability and appearance of the preparation.

          Frying and deep fat frying are particularly suitable for cooking low-fat,

young tender poultry and more frequently used than broiling. The halves of the

birds are frequently fried. Before frying they are coated with seasoned flour or

beaten eggs and bread crumbs. They are then carefully cooked to prevent over

browning before the meat is tender. If deep fat- fried, the bird must be steamed

until the stage of doneness before being dipped in flour or in egg and crumbs and

fried slowly. The time required for browning in deep fat is too short to promote

thorough cooking of meat.

Roasting:  Poultry may be roasted, stuffed or unstuffed. When the whole bird is

roasted, tender parts, such as the breast, may be over cooked before the legs

and thigs are cooked to the desired state. For stuffed birds, roasting should be

continued till the internal temperature of the stuffing reaches 74oC. This

eliminates the possibilities of bacterial food poisoning. When the poultry is

roasted without stuffing, it is cooked at an oven temperature of 163oC till the

internal temperature of the thigh muscle reaches 85oC.

Tandoor chicken: This is a well known and popular Indian chicken dish. This is

barbecued chicken. The cooking is done in a clay oven called a tandoor. Tandoor

is a long earthenware pot embedded in clay and earth. Charcoal is put inside and

the oven is made red hot. Other types of ovens are designed and used. Tender

chicken, either whole or cut, is used. The skin is removed from the chicken and

the flesh pricked with a fork and sprinkled with salt. Tandoor sauce is then

smeared on the chicken which is then left aside for 6-8 hours. It is then cooked in

the tandoor. Half way through the cooking time it is removed from the oven and

brushed all over nicely with butter or oil and cooked again until the chicken is fork

tender. Chicken cooked this way is delicious.

Braising and stewing:  The older tougher birds are cooked this way. Disjointed

pieces of chicken are generally braised. Generally they are first browned by

frying after which water is added and the bird simmered until it is tender. For

stewing, the whole bird or cut pieces are used. They are cooked in water with

seasonings and vegetables till they are tender. 

         

   

           

 

 

 

 

 

SPICES AND CONDIMENTS

Classification / Types

          Spices and condiments can be classified in different ways, such as,

according to their botanical families, economic importance, method of cultivation

or part of component of the plant, such as seeds, leaves, bark etc. Each system

has its own merits and demerits. A method of classification depending on the

origin and active principle present in the spices is as follows:

1.     Pungent spices:  pepper, ginger, chillies, mustard

2.     Aromatic fruits : Cardamom, nutmeg and mace, fenugreek, anise,

fennel, caraway, dill, celery, cumin, coriander etc.

3.     Aromatic barks: Cinnamon, Cassia

4.     Phenolic spices containing eugenol: Clove, all spice

5.     Coloured Spices : Paprika, saffron, turmeric

Use in Indian cookery

1.      Spices are mostly used as flavouring agents in a number of food stuffs

such as curries, bakery products, pickles, processed meats, beverages,

liquors etc. They enhance or vary the flavours of foods. Spices are also

flavour disguisers; they help mask the off-flavour of foods which, if

unspiced have to be thrown away.

2.      Some spices posses antioxidant properties while others are used as

preservatives in some foods like pickles and chutney.

3.      Others, like cloves and mustard, posses strong antimicrobial properties

and, as such prevent food spoilage.

4.      Spices were used to preserve meat for long periods when there was no

refrigeration.

5.      many spices also posses important physiological and medicinal

properties.

6.      Spices are also act as colouring agents. Turmeric is a common spice

which imparts a yellow colour to foods in which it is used. Saffron which is

the stigma of flowering plant, imparts an orange –red colour to food.

7.      Spices and condiments are acting as a appetizing and stimulating

functions.

8.      Some of the flavouring agents include vannila, and fruit flavourings like

lemon, orange, strawberry, rose etc, which are used in sweet preparations

such as halwas, ladus, cakes, ice creams etc.  

 

FOOD ADDITIVES

          FAO and WHO in 1956 defined food additives as non-nutritive substances

added intentionally to food, generally in small quantities, to improve its

appearance, flavour, texture or storage properties.

Functions and uses of food additives

          Food additives perform several functions such as drying, emulsifying,

enhancing flavour, enriching, firming, flavouring, foam producing, glazing,

leavening, lining food containers, maturing (flour), anticaking, antidrying,

antifoaming, antihardening, antispattering, antisticking, bleaching, buffering,

chillproofing, clarifying, colour retaining, colouring, conditioning (dough),

creaming, curing, dispersing, dissolving, sweetening, texturizing, thickening,

water-proofing, water retaining, whipping, acidifying, making alkaline,

neutralizing, peeling, plasticizing, preserving, pressure dispensing, refining,

replacing air in food packages, sequestering unwanted metal ions, stabilizing ,

sterilizing and supplementing nutrients. 

          The major uses of food additives are as under:

1.      Enhancement of the attractiveness of foods by means of colouring and

flavouring agents, emulsifiers, stabilizers, thickeners, clarifiers and

bleaching agents.

2.      Maintenance of nutritional quality, such as the use of antioxidants.

3.      Facilitating food processing by means of acids, alkalies, buffers,

sequestrants and various other chemicals.

4.      Enhancement of keeping quality or stability by the use of antioxidants, 

antimicrobial agents, inert gases, meat cures etc.

5.      Protection against food spoilage during storage, transportation,

distribution and processing.

Classification

          Antioxidants, chelating agents, colouring agents, curing agents, emulsions,

flavours and flavour enhancers, flour improvers, humecants and anticaking

agents, leavening agents, nutrient supplements, non nutritive sweeteners, pH

control agents, preservatives, stabilizers and thickeners.

Role of thickeners and stabilizers

          These compounds function to improve and stabilize the texture of foods,

inhibit crystallization (sugar, ice), stabilize emulsions and foams, reduce the

stickiness of icings on baked products and encapsulate flavours. Substances

used as stabilizers and thickeners are polysaccharides such as gum arabic, guar

gum, carageenan, agar agar, alginic acids, starch and its derivatives,

carboxymethylcelluloses and pectin. Gelatin is one noncarbohydrate material

used extensively for this purpose. Stabilizers and thickeners are hydrophilic and

are dispersed in solution as colloids. These swell in hot or even cold water and

help thicken food. Gravies, pie fillings, cake toppings, chocolate milk drinks,

jellies, puddings and salad dressings are some among the many foods that

contain stabilizers and thickeners.

Role of sweeteners

          Sucrose is an ideal sweeteners; it is colouress, soluble in water and has a

“pure” taste, not mixed with overtones of bitterness or saltiness. But it is rich in

calories. The diabetics and over weights who must restrict their intake of sugar

must have an alternative to sucrose. Thus, synthetic nonnutritive sweeteners

having less than two percent of the calorific value of sucrose for equivalent unit of

sweetening capacity came into use.

          The first synthetic sweetening agent used was saccharin, which is about

300 times sweeter than sucrose in concentrations upto the equivalent of a 10 per

cent sucrose solution.

          Use of saccharin often leaves a bitter and upleasant after-taste. Attempts

to find better substitutes resulted in the accidental discovery of cyclamates which

are about 30 times sweeter than sucrose but have little of the after taste of

saccharine. So cyclamates were widely used as sweetening agents in the

manufacture of soft drinks, other low- calories liquid foods and dietetic forms of

foods. However, the use of cyclamates has been banned after high dosages

were found to produce bladder cancer in rats, probably from the formation of

cyclohexylamine, a known carcinogen.

          Newer nonnutritive sweetening agents, ranging in sweetness from 10 to

3,000 times of sucrose have been discovered. Among them is glycyrrhizic acid,

obtained from the roots of a European leguminous plant glycyrrhiza glabra

(licorice). The sweet taste of glycyrrhizic acid is detectable at one fiftieth the

threshold taste level of sucrose. It is used in tobacco products, confectioneries

and beverages. Neohepsiridine dihydrochalcone isolated from citrus peels is

about 1,000-2,000 times as sweet as sucrose.

          The tropical African fruits, kutemfe and serendipity berry, contain low

calorie sweeteners. Kutemfe contains two proteins thaumatin I and II. On a molar

basis these substances are about 106 times as sweet as sucrose. They protein

substance, monellin obtained from serendipity berries, is as sweet as the

sweeteners from kutemfe. But these substances are unstable to heat and lose

their sweeteners at pH2 at room temperature.

          A potentially useful low calorie sweetener is the diester of L-aspartic acid

and L-phenylalanine. The methyl ester of L-aspartyl-L. phenylalanine, is reported

to the 100-200 times sweetener than sucrose with taste characteristics very

similar to those of sucrose.

Role of Emulsifiers

          Emulsifiers are a group of substances used to obtain a stable mixture of

liquids that otherwise would not mix or would separate quickly. They also

stabilize gas-inliquid and gas-in-solid mixtures. They are widely used in dairy and

confectionery products to disperse tiny globules of an oil or fatty (acids) liquid in

water. Emulsifying agents are also added to margarine, salad dressings and

shortenings. Peanut butter contains upto 10per cent emulsifiers. 

          One of the most widely used emulsifiers is lecithin which is found in milk,

egg and soyabean. Lecithin keeps, in milk, the butter fat and water phases more

or less uniform. Commercial vegetable lecithin is obtained principally from

soyabean. Lecithin is employed in the preparation of cocoa butter and chocolate

candy. The texture and keeping qualities of bread and other fermented baking

products are improved by the use of lecithin. Lecithin is a more effective

emulsifying agent in combination with monoglyceryl sterate and ascorbic acid. A

number of mono-and diglycerides and their derivatives are good emulsifying

agents. In these cases, the ester groups make the molecule fat soluble, while the

alcohol group lends water solubility to another portion of the molecule. As a

result, the molecule can serve as a bridge to keep fat molecules suspended in

water.

          In addition to these natural emulsifiers, there are a number of synthetic

ones. These include propylene glycerol monosterate, sorbitan monosterate and

polysorbates.

Role of leaveners

          Leavening agents produce light fluffy baked goods. Originally, yeast was

used almost exclusively to leaven baked products. It is still an important

leavening agent in bread making. When yeast is used, ammonium salts are

added to dough to provide a ready source of nitrogen for yeast growth.

Phosphate salts are added to aid in control of pH.

          Chemical leavening agents (NaHCO3) are used to make light cakes,

biscuits, waffles, muffins and many other baked products. Baking powders

generate CO2 for leavening purposes.

Role of colours

          Colour are two types- Synthetic colours and natural colours. Even though

colours add nothing to the nutritive value of foods, without colours most

consumers will not buy or eat some foods. Thus, colours are frequently added to

restore the natural ones lost in food processing or to give the preparations the

natural colour we expect.

          Originally, many colour additives were natural pigements or dyes. For

example, spinach juice or grass, marigold flower and cochineal were used to

obtained green, yellow and red colour respectively. This gave place to synthetic

dyes obtaine from coal tar. Synthetic colours generally excel in colouring power,

colour uniformity, colour stability and cost. Further, in many cases natural

colouring materials do not exist for a desired hue. Carbonated beverages, gelatin

dessert, candies and bakery goods are some foods that are coloured with coaltar

dyes. As a number of coaltar compounds have been shown to be potent

carcinogens, the use of coaltar dyes as food additives is restricted.

          A number of natural food colours extracted from seeds, flowers, insects

and foods are also used as food additives. One of the best known and most

widespread red pigment is bixin, derived from the seed coat of Bixa orelana, the

lipstick pod plant of South American origin. Bixin is not considered to be

carcinogenic. The major use of this plant on a world wide basis, however, is for

the annatto dye, a yellow to red colouring material extracted from the orange-red

pulp of the seeds. Annatto has been used as colouring matter in butter, cheese,

margarine and other foods. Another yellow colour, a carotene derived from

carrot, is used in margarine. Saffron has both flavouring and colouring properties

and has been used for colouring foods. Turmeric is a spice that gives the

characteristic colour of curries and some meat products and salad dressings. A

natural red colour, cochineal obtained from extracted by the insect (Coccus

cacti), grape skin extract and caramel, and the brown colour obtained from burnt

sugar, are some natural colours that are used as food additives.

Role of preservatives

          A preservative is defined as any substance which is capable to inhibiting,

retarding or arresting the growth of microorganisms, of any deterioration of food

due to microorganisms or of masking the evidence of any such deterioration. The

compounds used as preservatives include natural preservatives such as sugar,

salt, acids and synthetic (chemical) preservatives like potassium metabisulphite,

benzoic acid, nitrate and nitrite, sorbic acid, acetic acid, proponic acid etc. In the

fruits and vegetable processed foods potassium metabisulphite, benzoic acid and

acetic acid is commonly used. Nitrate and nitrite is used in the curing of meat.

Sorbic acid and proponic acid is mostly used in cheese, baked products and

pickles. The chemical preservatives are generally added after the foods are

processed.

Role of flavouring agents and flavouring enhancers

          Flavouring additives are the ingredients, both naturally occurring and

added, which give the characteristic flavour to almost all the foods in our diet.

Flavour enhances are not flavours themselves but they amplify the flavours of

other substances through a synergistic effect. Flavour and flavour enhancers

constitute the largest class of food additives. These are about 2,100 approved

natural and synthetic flavours of which more than 1,600 are synthetic ones.

          Natural flavour substances, such as spices, herbs, roots, essences and

essential oils have been used in the past as flavour additives. The flavours of

such materials are not uniform. They vary with the season and area of

production. Natural food flavours are thus being replaced by synthetic flavour

materials.

          The agents responsible for flavour are esters, aldehydes, ketones,

alcohols and ethers. Generally most synthetic flavours are mixtures of a number

of different substances. For example, one imitation cherry flavour contains fifteen

different esters, alcohols and aldehydes.

          The most widely used flaovur enhancers is mono sodium glutamate

(MSG), the sodium salt of the naturally occurring amino acid glutamic acid. This

is added to over 10,000 different processed foods and it has an attractive meat-

like flavour. This has been in use in Chinese and Japanese cooking for centuries,

and was extracted from seaweeds and soybean.

        

FOOD FORTIFICATION

Need for food fortification

          In India cereals are staple food. Very little care is however given for the

consumption of fruits and vegetables. Malnutrition is therefore is more prevalent

in the third world countries. Vitamin A deficiency, iodine deficiency disorders,

folate malnutrition and iron deficiency anemia are among the most common

forms of micro nutrient malnutrition. The scientists are thus in search of

technology which can provide enough nutrients and protect people from

malnutrition. Fortification of food is one such novel technology which fulfils both

the need.

          Micronutrient malnutrition is caused by low intake of food rich in

micronutrients and food substances like vitamin C that enhance absorption. High

intake of factors like phytates and tannin inhibit absorption. High incidence of

measles, diarrhoea and parasitic infections and maternal deficiencies also cause

micronutrient malnutrition. The main strategies to overcome malnutrition is food

fortification is the one technology recommended by WHO.

Food fortification

          Food fortification is a process where by one or more nutrients are added to

foods to maintain or improve the quality of diet. It is also known as food

enrichments or nutrification. The Codex Alimentarious Commission in 1987

suggested the following guidelines and basic principles for essential nutrients.

1.        To replace losses that occurs during manufacturing and handling of

foods for example removal of cream from milk takes almost all of the

vitamins A and D and therefore skimmed milk may be fortified with the

same vitamins.

2.        To ensure nutritional equivalence in imitation or substitute foods;

3.        To compensate for naturally occurring variations in nutrient levels;

4.        To provide levels higher than those normally found in food for example

margarine is fortified with vitamin A and D.

5.        To provide balanced intake of nutrients in special cases eg. Infant

foods, foods for athletes, medical foods etc.

In addition to the above mentioned objectives, nutrients may be added to

perform specific processing functions. -carotene is added to products such as

juices, pasta, margarine, cakes, processed cheese to impart colours. Vitamin E

can be used as an antioxidant.

Application

Criteria for selecting food vechicle

     Food fortification is appropriate when there is a need for increasing the

intake of essential nutrients.

     The fortified food must be consumed by a large section of the population.

     Relatively inter and intra individual variation occurs in the amount of the

fortified food consumed.

     The essential nutrients should be present in amounts that are neither

excessive nor insignificant.

     The nutrient added should not adversely affect the metabolism of other

nutrients.

     The nutrient added should be sufficiently stable in the food.

     It should not impart adverse texture to the food.

     Nutrients should be added in controlled condition and should have minimum

cost.

     The marketing and distribution channels must be such that the food

reaching to consumers ca be tracked.

Fortification technology

          Foods can be fortified with nutrients either in powder or liquid form. Micro

encapsulation techniques enable fat soluble vitamins to be produced industrially in a

hydro-dispersible form. Sugar, wheat flour, salt, tea, water, bread and juices are normally

selected as food vechicles for food fortification. The foods fortified with vitamin A, iron,

iodine and multinutrient mixes are of follows:   

Nutrient Ongoing Experimental

Vitamin A Sugar Whole wheat, rice, tea, oil,

salt, MSG

Iron Wheat flour, corn flour infant

formula rice

Sugar, salt, milk, biscuit,

water, fish sauce, curry

powder, maize meal, MSG

Iodine Salt, tea, water, bread, milk Sugar

Multinutrients - Wheat flour, corn meal

wheat flour, noodles 

          The techniques of food fortification depend on the food processing

technology used:

     Dry mixing:  for foods like cereals, flour and their products, powder milk,

beverage powders.

     Dissolution in water: for liquid milk, drinks, bread, pastas, cookies.

     Spraying: for corn flakes and other processed foods requiring cooking or

extrusion steps.

     Dissolution : in oil

     Adhesion :  for sugar

     Coating:  for rice. The vitamins sprayed over the grain must be coated to

avoid losses when the grains are washed before cooking.

     Pelleting for rice: The vitamins are incorporated into pellets reconstituted

from broken kernels. 

References

Benion, M. 1990. Introductory Foods, 8th Edn., The Macmillan Co. London.

Benion,M. 1982. The Science of Foods- The Macmillan co., London.

Meyer, L.h. 1991. Food chemistry. Affiliated East- West Press Pvt. Ltd., New

Delhi.

Swaminathan, M. 1995. Food Science and Experimental Foods, Ganesh and

Co., Madras.

Potter, N. 1987. food Science., CBS publishers and Distri butors, New Delhi.