Block-3: Corn, barley, oat, millets, pulses and oilseeds processing

Unit-9: Composition and processing of Corn Unit-10:Barley, Oat and Millet processing Unit-11: Composition and utilization of PulsesUnit-12:Oilseeds and related products Dr. Mita SinhamahapatraSOA, IGNOU*

COMPOSITION & PROCESSING of CORN*

Structure of cornTip cap:(0.8% of kernel wt) provides point of attachment to cob.Bran: (5-6% of kernel wt) thin outer covering of kernel.Germ/embryo: (10-12% of kernel wt) only living part of kernel. contains lipids (7-8% corn oil), enzymes, vitamins and minerals. Endosperm: (82-84% of kernel wt) contains 86-89% starch, protein. Outer layer is aleurone layer rich in minerals and proteins.

*

Corn compositionCarbohydrates: Starch is major carbohydrate (72-73% ). also contains sucrose, glucose and fructose. 2.5%. Crude fibre present.Lipids: Lipid content ranges from 4-5%, in some hybrid varieties up to 7-8%. Triglycerides are major fraction, other lipids are phospholipids, glycolipids, hydrocarbons, sterols, free fatty acids, carotenoids, tocols and waxes.Proteins: protein is known as zein (7-8%). deficient in lysine, tryptophan & low in threonine, valine & sulphur containing amino acids.Minerals: contains P, K, Mg, S, Ca, Na, I, Fe, Zn etc. About 78% of minerals of kernel are concentrated in germ.Vitamins: Corn contains vitamin A (-carotene), vitamin E, thiamine, riboflavin, pantothenic acid, biotin, folic acid, niacin and pyridoxine.

*

General Composition of Corn Kernel*

Moisture, %15.0-16.0Starch, %67.8-74.0Protein, %8.1-11.5Fat, %3.9-5.8Fiber, %3.0-4.0Ash, %1.37-1.5

Types of cornFlint corn: have mostly hard, glassy endosperms with smooth, hard seed coats.Flour corn: endosperms are made of soft starch with thin pericarps.Dent corn: flinty sides and soft cores of starch that cause the end of the kernels to collapse or dent during drying.Pop corn: small kerneled flint type corns, have very hard endosperm.Sweet corn: wrinkled, glassy appearance, have sugary gene that retard conversion of sugar to starch during endosperm development.Waxy corn: carries a gene that produces 100% amylopectin.

*

Endosperm distribution in 5 types of corn kernels*

Harvesting and StorageCorn is generally harvested at moisture content below 26% (wb) and dried naturally. It may also be dried artificially using mechanical dryers. Safe storage moisture content is around 15%.Dried shelled corn is stored in bins, tanks, silos and pits. During storage, temp, humidity and air movement should be controlled to prevent post harvest loss.Factors responsible for post-harvest losses: spoilage due to microbial attack, insect and rodents attack due to improper storage. Generally, anti-microbial sprays and insecticidal sprays and chemicals are being used to protect the corn during storage. *

CORN MILLING AND PROCESSING*

Corn Dry-MillingCommercially, dry corn millers use one of three processes as follows:Tempering-degerming processStone-ground or nondegerming processAlkaline-cooked process

*

Corn Dry-Milling Process*

Dry milled products & their applicationsGrits, meals, and flour consists of primarily starch & protein, main difference is difference in particle size*

Milled productApplicationsCharacteristicsFlaking gritsCorn flakesCoarse granulation. Yellow corn with non fissured, vitreous endosperm to provide higher yield of gritsGritsas porridge, snack food, brewers gritsApprox. balance of granulation to provide reasonable cooking time and homogenous cooked texture without causing formation of lumpsMeal & flourTortillas, bread mix, pasta, snack foods, flat breadsFiner particle size with wide variation.

Wet milling of corn*

SteepingSoaking of corn in water up to about 45% mc (wb).Tempering temperature and time are to be controlled carefully as they are critical for penetration of water.Additionally, treatment of water with SO2 (0.02-0.03%) is carried out, which further hasten up moisture penetration and is also thought to be responsible for breaking up of protein matrix surrounding starch granules. SO2 also prevents growth of undesirable microbes.Steeping is carried out in tanks, and steep water with corn soluble is sent for concentration through evaporation. The residue obtained has nutritive value for feed rations.*

Germ separation & fractioningSteeped corn is ground in disk mills to release germ without damage. Due to high moisture, process of germ dislodging is gentle.Ground material slurry is taken to a separating medium for separation into light and heavy fractions using hydroclones.Lighter material (germ) exits as overflow while heavier fraction is removed from bottom.Germs are then dried and processed for oil extraction and meal.Heavier fraction is moved to the next step of fibre removal.

*

Fibre separationCorn slurry after germ separation is passed through finer screens to separate fibre (mostly hull) from starch and protein.Large sized particles that are unable to pass through screen consist of primarily fibre and some particles of starch and fibre attached to each other. The remainder of slurry passes through the next step of starch and protein separation.Large sized fibre and starch particles are passed through impact or attrition mill to detach each other. After milling, slurry is sent to multistep fibre wash system consisting of several screens for washing starch from fibre.Fibre is sent for removal of water and concentration of solids using screen centrifuges.

*

Starch and protein separationSlurry after separation of fibre is pumped to disk-nozzle type centrifuges, where heavier starch is separated from gluten. Gluten is dewatered using additional centrifuges and vacuum filters.Separated starch slurry may contain some protein and impurities, which can be removed by starch-washing hydroclones using fresh water. Excess wash water is then removed by centrifugation and/or vacuum filters to get purified starch.Wet-milling not only fractionates corn into its constituents but also converts some of these fractions into syrups and ethanol and other chemicals by fermentation process and therefore is known as the ''corn-refining" industry.

*

CORN PRODUCTSCorn flakes: popular RTE breakfast cereal product. A mixture of corn grits, syrup, sugar, malt, salt & water is pressure-cooked for 1-2 hr. Cooked grits are dried at 66C and tempered for 6-24 hr. Grits are flaked in rollers and toasted at 320C for 50 sec or 288C for 2-3 min. Flakes are cooled, sprayed with nutrients and immediately packed. Extrusion may be done to produce corn flakes.

Corn Meal/Corn Flour: ground from dried corn. a common staple food, and is ground to fine, medium, and coarse consistencies. It can be indefinitely stored in an airtight container in a cool, dry place.Yellow cornmeal, White cornmeal or Blue cornmeal are variety.

*

Corn Products- cont..Corn Syrup: produced by acid or acid-enzyme hydrolysis. Corn starch slurry is treated with dilute HCl and heated at 140-160C for 15-20 min under pressure. Currently, -amylase and glucoamylase are added for syrup production. It is used as a thickener, sweetener, and humectant. It is also used to soften texture, add volume, prohibit crystallization and enhance flavour.

Corn oil: extracted from germ. used in cooking, specially frying; margarine and also a source of biodiesel. It has a milder taste and is less expensive. Refined corn oil is rich in PUFA and MUFA.

*

Corn Products-cont..Corn Starch: contains 25-30% amylose and 70-75% amylopectin. used as thickening & gelling agent in food; in paper, and adhesives.

Modified Starches: modified to improve functional characteristics. Acid modification reduces viscosity but retains a strong tendency to gel on cooling, used in gum candies, paper coatings, and textile.Oxidized starch (using sodium hypochlorite) retains granule structure, produces clear pastes with reduced thickening tendency on cooling, and produces clear tough films, used in laundry starches and paper.Dextrinized starch (by dry heating) have reduced viscosities, cold water solubility and produce tacky films. Used in paper products.Pregelatinized starch (by cooking) does not need for additional cooking and used in instant puddings.Derivatized starch is produced by cross-linking and stabilization to modify gelation and cooling characteristics of granular starch .

*

Corn Products-cont..Corn Sweeteners:Starch can be hydrolyzed to glucose syrups and further converted to crystalline sugars. Once saccharified to appropriate degree, syrup is filtered to remove residual protein, passed through activated carbon to remove color and flavor compounds and also demineralized using an ion-exchange column. Then syrup is concentrated and dried to produce corn syrup solids or crystallized to produce dextrose monohydrate. Glucose syrup can be transformed into high fructose corn syrup (HFCS) by treating with glucose isomerase. HFCS contains 42% fructose, 50% glucose, and 6% higher saccharides. 55% HFCS is used in soft drink; 25% HFCS is used in bakery products, fruit drinks, canned foods, frozen desserts, and other dairy products.

*

BARLEY, OAT & MILLET PROCESSING*

BarleyIt is considered one of the oldest cereal plant cultivated by early men. two forms: wild and cultivated. Hordeum. vulgare and H. distichum having six and two grain rows on a spike respectively. In India, cultivation of six rowed barley dominated. On the basis of adherence of hull with kernel, hull less or naked barley (more useful for direct food uses) and hulled variety (choice for malting and brewing).It is also used as animal feed.

*

Malting of BarleyGeneral specifications sought in malting barley Min 90% grains should have size > 2.5 mm with almost 99% purity in variety, Protein content 9.0% to 11.5%, Max. moisture content 13.0%,Min 97% germination after 3 days,-glucan content maximum 4%. *

SteepingSoaking of barley grain in sufficient amount of water to prepare the grain for optimum germination. Grain preparation largely depends on water grain ratio, temperature of soaking, time of soaking, aeration and agitations. Generally steeping takes 2 to 3 days but free water of steeping vessel is drained and replaced every 6 to 9 h. Stepping causes 0.5 to 1.5% loss of total dry matter of barley. Steep water temperature varies between 5 to 18C. It is also recommended to aerate and agitate barley by compressed air for 4 to 5 times in a day for around a span of 45 minutes.

*

GerminationGermination refers to physiological process of formation of rootlet from barley. Barley is taken out from steeping tank immediately after steeping to facilitate biological changes. These changes require optimum control of moisture, air and temperature. Commercially, a separate germinating compartment is used. Traditionally, germination trays are used in some cases. Germination completes within 4 to 6 days. Generally, increase in rootlet size around two-third of the kernel is taken as deciding factor in judging completion of germination.*

Kilning or dryingDrying of germinated barley is carried in three stages. 1st stage: a rapid evaporation of water is made by hot air of 48 to 60 C. Frequent turning of barley layers is made to facilitate uniform drying. Moisture level is reduced from 48% to 23%. 2nd stage: temperature is increased up to 71C and moisture content is reached close to 12% level. 3rd stage:temp is increased to 88C to bring final moisture content 3.5 to 5.0% for brewers malt and about 6.0% for distillers malt. Malt is cooled after third stage of drying using ambient air or air around 35C.Moderate heating during drying develop a desirable malt flavor.

*

CLASSIFICATION OF MALTBased on colour of malt:White malt- is a light pale coloured and mild flavoured malt; requires relatively lower drying temp, used for pale and some light coloured distilled beverages.Dark malt- has dark pale to brown colour and possesses a slight bitter flavour, requires higher drying temperature, used in dark beers as mixture in the total malt.Amber malt, chocolate malt etc Based on diastatic power of malt:Diastatic malt: contains enzymes that break down starch into sugar. Used in bakery ingredient.Non-diastatic malts: has pre-inactivated enzymes and is used primarily for flavoring malt based beverages. *

Use of Barley and Oat as Breakfast CerealsOat FlakesOat mealPuffed CerealsMultigrain Product: multigrain bread and biscuits, multigrain flours, baby foods, junior foods and extruded snacks Extruded Snacks*

MilletsMillets (coarse grain) have lesser economic value than other cereals. Seeds are enclosed in hull which is usually hard and indigestible. Can be cultivated in dry areas. Varieties of millets: Finger millet, Pearl, Great millet etc.Can be used as human food & feed for poultry, livestock, and fish, They contain 11% protein, B group vitamins and minerals likecalcium,iron,potassium, magnesium, andzinc. Few types of millet have higher nutritional value than wheat. (P and Fe content; methionine content). Millets do not containgluten, so they can be thought of gluten free preparations. They contain anti-nutritional substances like phytate, polyphenols, amylases and proteases inhibitors etc.*

*

CharactersFinger MilletPearl MilletSorghumBotanical NameCaesalpinia cucullataPennisetum glaucumSorghum bicolorCommon NamesAfrican millet orRagi or Red MilletSpiked Millet or BajraGreat Millet or JowarCommon Indian States for Cultivation Karnataka, Orissa, Tamil Nadu and UPRajasthan, Haryana Maharashtra, UP AP, GujratKarnataka, MP, Rajasthan, Tamil Nadu

Chemical composition of millets*

CharactersFinger MilletPearl MilletSorghumProtein (%)7.313.312.3Fat (%)1.36.33.6Carbohydrate (%)7268.473.8Ash (%)2.71.71.7Mineral (mg/100 g)398 Calcium, 3.9 Iron17 Calcium, 9 Iron 15 Calcium, 4.2 Iron Dietary Fibre (%)182014

Food usage of milletsMillets are considered as poor mans food.Pearl millet and ragi, are used to make breads particularly flat breads or unleavened roti. Ragi flour is also made into leavened dosa. Ragi can be ground and cooked into cakes, puddings or porridge. Sorghum can have functional advantages including processing properties similar to rice for use in snacks, breakfast cereals.

*

Composition &utilization of PULSESPulses (dry split seeds or dhal ) cover all those grown for their dried seeds and popularly consumed as a routine dietary item.Important source of protein predominantly for vegetarian population.For economic and social reasons, Indians largely depend on pulses as a source of proteins, minerals and vitamins in their daily diet.Legumes are used as: food; fodder; source of oil; soil fertilizer.India is ranked among major pulse producing countries in the world.Chickpea, pigeonpea, mung bean, urad bean, lentil, and pea are important pulses crop in the country. Chickpea and pigeonpea collectively contribute around 60% of total pulse production. *

Chick pea/Chana/ Bengal gramPea/MatarGreen gram/ MoongPigeon pea/ Arhar/ TurRed gram/ Masoor/lentilBlack gram/ Urd*

Kheasri Hyacinth bean/ SemKidney bean/ RajmaCow pea/ LobiaSoybean Horse gram/ kulthe*

Various legume pulses of India

*

English NameLocal NameEnd uses/Forms of UsePigeonpeaArahar, TurDry seeds as dhalChick pea/ gramChana(brown/desi & white /kabli) Dhal, Flour (besan), Fodder, Raosted, Sprouts, BoiledLentilMasoorWhole and splits as DhalGreen GramMung, MoongDhal, Sprouts, Boiled, Dessert or sweetsBlack gramUrd, Udid, MashDhal, Vada, Idli, DosaPeaMatarGreen pods, Canned, Flour, Dried whole, BoiledCow peaLobiaGreen pods as veg, Dry seeds as PulseHorse gramKultheFodder, As a diureticChickling vetchKhesari, KesariDhal, As an adulterant in Arahar Kidney/French beanRajma, Vilayati semGreen/whole dry seed is cooked as vegetableHyacinth beanSemGreen pods as veg, fried/roasted seeds SoybeanSoyaDhal, Flour, Paneer

Structure of SoybeanStructure of Pea*

Composition of common pulses

*

ConstituentsEstimate (g per 100 g of edible portion)Pigeon peaLentilGreen GramBlack gramPeaSoybeanMoisture7-1010-1210-1110-1110-148Protein16-2024-2520-2422-2410-1325-40Fat1-41-21-1.51-21-218-20Carbohydrates40-6558-6156-6056-6049-6221-32Fibre5-910.540.510.540.53-4Ash40.52-330.520.52-350.5

Anti-nutritional & toxic factors of pulsesProtease inhibitor: Pulses chiefly contain trypsin and chymotrypisn inhibitors. Chickpea & pigeon pea contain highest amount followed by soybean, peas & common beans. These are heat labile, thus cooking (with mango or tamarind) inactivates these. Amylase Inhibitors: chickpea, pigeonpea, mung, urd and lentil have variable levels of these. Cooking of pulses may inactivate these.Flatulence Causing Oligosaccharides: oligosaccharides (raffinose, pentosans and verbascose) in pulse escape digestion in gut (because Human GI tract does not have -galactosidase) and are fermented in large bowel and produce gas/flatulence. Chickpea contains these. Overnight Soaking, germination and cooking reduce these sugars. Phytolectins: these interact with glycoprotein of RBC and cause haemaagglutination. Hydrothermal processing eliminates these.

*

Anti-nutritional & toxic factors cont..Polyphenols: polyphenolic compounds present in pulses reduce protein digestibility. Decortication, soaking, germination and cooking reduce these. Phytic acid and Phytates: these bind with Ca, Zn, Mg and inhibit their absorption. These can be removed during soaking. Cyanogenic Glycosides: liberate hydrogen cyanide by action of -glucosidase. pigeon pea & chickpea may have these but below the toxicity level. Cooking can inactivate these.Lathyrogens: neurotoxin (BOAA) responsible for lathyrism. toxin is associated with khesari dhal. Consumption of khesari dhal more than 300 g/person/day can cause lathyrism in humans. cooking of dehulled seed in excess water with part draining or heating / roasting at 1500 C for 20 min may remove /lower toxin.

*

Remedy of anti-nutritional factorsMilling: include dehulling and/or splitting into two halves. Reduces level of polyphonolic compound present in seed coat. Soaking: soaking in water with salt and /or alkali can remove protein inhibitors and flatulence causing oligosaccharide; increases digestibility; reduce cooking time; increases Vit C. But causes loss of some desirable nutrients . Soaking temp, time, medium and type of pulse are important. Germination: increase in nutrients in sprouted pulses specially vitamins, minerals and protein and decrease in calories and carbohydrate content. It eliminates Phytates & raffinose and lower activity of phytolectins.Fermentation: During fermentation, enzymes present in pulses ( -galactosidase and phytase) reduces raffinose oligosaccharides and phytic acid. Cooking: inactivates heat sensitive anti-nutritional factors- protease inhibitors, phytolectins and cyanogenic glycosides. *

Milling Of

pulses *

Oilseeds and processing*

Plant sources of oils Linseed Niger Cotton seedSesameMustardCastor Rapeseed/canola*

Plant sources of oilSoybean SunflowerOlive Palm Ground nutCoconut *

Productivity: India and world (tonnes/ hectare)Indias share: 27% for groundnut, 23% for sesame, 16% for rapeseed and 66% for castor seed. Groundnuts in shell form 11% of world exports and sesame forms 17%. Indias share in World oilseed production*

OilseedsIndiaWorldHighestSoybean0.852.293.28(EU-15)Cottonseed0.591.062.07(Australia)Groundnut0.591.022.13(China)Sunflower0.621.181.73(EU-15)Rapeseed/Mustard0.751.492.96(EU-15)

Processing of edible oils/fats

ExtractionRefiningBleachingHydrogenationFractionationDeodorizationPlasticization

*

Extraction from oil seeds

After cleaning, seeds are dehulled except small sizes seeds (canola and rapeseed). Seeds are ground/rolled to flakes and then heated/cooked (80 to 1050C).Oil is extracted by:a) Screw press extraction: mechanically expels the oil from the seed that contains high amount of oil. pressed cake contains 3-10% oil. b) Pre-press solvent extraction : removes portion of oil with expellers, and left out oil is extracted with an organic solvent. Pre-pressed cake contains 15-18%.c) Solvent extraction: removes oil from pre-conditioned oilseeds with an organic solvent (hexane, isopropyl alchool) followed by distillation of solvent. Oil bearing fruit extraction: olives are ground/milled to a course paste and then oil extracted by hydraulic press, continuous centrifuges, or adhesion filtering. palm oil is extracted by cooking and pressing.*

Oil extraction by Screw press or Hydraulic pressCleaningHydraulic pressingSize reductionFlakingConditioningScrew pressingOil Oilseed cake*

Screw pressCooked seed flakesCrude oil Main worm shaftknifecakeAdjustable cone for press-cake outletCone shaped pressure cage *

Solvent extraction*

Diagram of countercurrent flow. (Copyright: Crown Iron Works Company, 2011).*

Pre-press solvent extraction *

Chemical Refining of oilFree fatty acids FFA, phosphatides, and others are removed with an alkaline solution(NaOH). FFA are converted into water-soluble soaps. Phospholipids, carbohydrates and proteins can be changed to water-soluble substances with hydration. Then fats and oils are washed with water to remove residual water soluble soaps. For removal of soap, mixture of fat and soap is passed through a continuous centrifuge machine that separates fat or oil from soap, which is referred as foots. refined oil is washed to remove final traces of soap and is centrifuged again. Finally, refined material is dried to remove residual water. *

Physical refining of oilFree fatty acids are removed by distillation during deodorization, and phosphatides and undesirable components should be removed before steam distillation.Degumming process involves treatment of crude oils, with water, enzymes, caustic soda, acids such as phosphoric, citric, or maleic to remove phosphatides, waxes and other impurities. Degumming converts phosphatides to hydrated gums that are insoluble in oil and can easily be separated.

*

Refining of oil*

*

*

Bleaching

Removal of pigments, non-pigment materials such as soap, gums, metals, peroxides and secondary oxidation products. Parameters affecting bleaching process: bleaching method, adsorbent type and dosage, time, temp, moisture and filtration. Batch method under atmospheric pressure: oil is pumped into an open steam jacketed tank and then bleaching earth is added from top. Temp. is raised to bleaching temp for a short period of time. oil is passed through filter press and then back to tank until oil is clear. Batch method under vacuum: uses lesser clay, can operate at lower bleaching temp and evacuate moisture quickly.Continuous method: is preferable because large quantity of oil can be processed without interruptions.Adsorbents used: natural bleaching earth or clay (Bentonite clays or Fullers earth), activated earths, activated carbon, and synthetic amorphous silica. *

Bleaching procedureVacuum drying*

Hydrogenation

Artificial saturation of refined oils to harden them into spreadable products. Eg. shortening.

Aim: to increase oxidative stability and convert liquid oils to shortening for greater use in various food products. Oils may be selectively hydrogenated by careful selection of temp(121-2320C), pressure (10-60 psi) and type of catalyst (usually nickel). Partial hydrogenation can be carried out in a controlled manner by selective hydrogenation (saturation of double bonds in the most unsaturated fatty acid before that of a lesser unsaturated fatty acid)Fully hydrogenated oils are solid & hard at room temp. Partially hydrogenated oil is thicker/stiffer than the non-hydrogenated oils.

*

Fractionation

To eliminate a fraction from a fat or oil which is the cause of undesirable properties. It separates into fractions of different melting points. a)Dry fractionation: includes dewaxing, hydraulic pressing, crystal fractionation and winterization. crystallization takes place without solvent and mixture of triglyceride is separated into two or more different melting fractions based on solubility at a given temperature. Winterization is a separation process that removes higher melting point crystals (triglycerides or waxes) which causes turbidity of oils during winter/refrigeration. Used for cottonseed oil & partially hydrogenated soybean oils. De-waxing is done to remove small quantity of waxes from oils rich in unsaturated fatty acids (sunflower oil). Hydraulic pressing removes small quantity of liquid oil from large quantity of solid fats. used to produce hard butter and specialty fats from palm kernel and coconut oil.*

Fractionation-cont..Solvent fractionation: crystallization of fraction by dissolving in a solvent. More yield of high quality solid fraction but needs high capital investment. Used for cocoa butter equivalents, medium chain triglycerides, high stability liquid oils etc. c)Detergent fractionation: crystallization is based on principle of dry fractionation. But, separation is accomplished by adding an aqueous detergent solution, containing a surfactant and an electrolyte which preferentially wets crystals into aqueous solution. It is more expensive but results in a higher yield.

*

Winterization*

DeodorizationIt is a vacuum steam distillation process for removing undesirable flavours and odours, mostly arising from oxidation. Odoriferous substances are FFA, aldehydes, ketones, peroxides, alcohols & other organic compounds (concentration 0.1 to 1.0%)All commercial deodorization process whether batch, semi continuous or continuous consists of steam stripping. Steam under reduced pressure removes volatile compounds from fats and oils. Higher temp result shorter deodorization times, but excessive temp may result in polymerization, isomerization, thermal decomposition, color reversion and distillation of tocopherols and some other antioxidants.In general, temp varies from 204 to 2460C and in some case this may go to the extent of 2460C. The absolute pressure between 2 to 4 mbar is commonly generated.

*

PlasticizationThis is important to develop a fine needle like crystal structure in order to produce smooth and firm consistency of plastic shortening. Plastic substance behaves as a solid under specific stress but yields at once and flows like a liquid when subjected to deforming stress above a minimal value.This may be carried out by chilling of properly formulated fat rapidly in scraped wall heat exchanger.During this rapid cooling, vigorous agitation is made to whip air in an amount of 10-15% to increase volume of shortening. *

*

*

References/Acknowledgementhttp://lipidlibrary.aocs.org/processing/solventextract/index.htmhttp://lipidlibrary.aocs.org/processing/alkrefining/index.htmhttp://www.wilmar-international.com/library/http://agritech.tnau.ac.in/postharvest/pht_pulses.html*

**