THE HEAT COAGULATION OF MILK.* The coagulation of milk by ...
Prop of Milk
-
Upload
thirumangai6 -
Category
Documents
-
view
225 -
download
1
Transcript of Prop of Milk
PROPERTIES OF MILK
MILKMilk may be defined as the whole, fresh, clean, lacteal
secretion obtained by the complete milking of one or more healthy milch animals, excluding that obtained 5 days after calving or such periods to render the milk colostrum free.
The term Market Milk refers to the fluid whole milk that is sold to individuals usually for direct consumption. It excludes milk consumed on the farm and that used for the manufacture of dairy products.
Milk production India's milk production increased from 21.2 million MT in 1968-69 to
100.9 million MT in 2006-07 and to 102 million MT in 2007-08. Today, India has the world's largest dairy herd (composed of cows and
buffaloes), at over 304 million strong and stands first in milk production, with 112.5 million tonnes of milk produced in 2009-2010.
India is also the third largest egg-producer in the world, at over 180 million eggs being produced every day or 65.7 billion eggs for the year 2011-12, and the world’s sixth largest producer of poultry meat.
Per capita availability of milk was 246 grams per day in 2006-07 increased from 241grams per day in 2005-06, up from 112 grams per day in 1968-69.
India's 3.9 percent annual growth of milk production between 1996-97 and 2006-07 surpasses the 1.8 per cent growth in population; the net increase in availability is around 2 per cent per year.
Indian dairy sector contributes the large share in agricultural gross domestic products.
Presently there are around 70,000 village dairy cooperatives across the country. The co-operative societies are federated into 170 district milk producers unions, which is turn has 22-state cooperative dairy federation. Milk production gives employment to more than 72mn dairy farmers.
Milk Production in India
Year Production (Million Tonnes) Per Capita Availibilty (gms/day)
1991-92 55.7 178
1992-93 58.0 182
1993-94 60.6 187
1994-95 63.8 194
1995-96 66.2 197
1996-97 69.1 202
1997-98 72.1 207
1998-99 75.4 213
1999-2000 78.3 217
2000-01 80.6 220
2001-02 84.4 225
2002-03 86.2 230
2003-04 88.1 231
2004-05 92.5 233
2005-06 97.1 241
2006-07 100.9 246
2007-08 104.8 252
2008-09 112.2 266
2009-10 116.4 273
2010-11 121.8 281
2011-12* 127.9 291
Source: Department of Animal Husbandry, Dairying & Fisheries, Ministry of Agriculture, GoI Note : * - Anticipated achievements
TYPES OF MILK
Milk is processed on the basis of the maximum content of fat and solid not fat (SNF) it would ultimately possess.
Standardized milkWhole milkReduced - fat milkLow - fat milk (1%) Skimmed milk / non – fat milk
Standardized milk- This is made by combining buffalo milk and skimmed milk. The fat percentage is maintained at 4.5% while the SNF is 8.5%.
Whole milk: Whole milk must contain at least 3.25% milk fat and 8.25% milk solids by weight—which means it derives about 50% of its calories from fat. Because of this relatively high fat content, whole milk is best used only for infants and young
children up to age 2.
Reduced-fat milk (2%): This milk contains 2% milk fat. The percentage of milk fat refers to the percentage of fat by weight, and much of milk's weight is water. Once you subtract the water from 2% milk, for example, you're left with a product that contains 20% fat by weight; such milk actually derives 35% of its calories from fat. Drinking 2% milk is a good way to wean oneself from whole milk at first, but is too high in fat as a permanent choice, unless your diet is otherwise very low in fat.
Low-fat milk (1%): One-percent milk gets 23% of its calories from fat. Many people find low-fat milk more appealing and a good compromise.
Skimmed milk/non-fat milk: This type of milk has as much fat removed as possible. It may not contain more than 0.5% milk fat by weight, and usually contains less than 0.5 gm of fat per cup, deriving just 5% of its calories from fat. Skimmed milk has about half the calories of whole milk. It is the best choice for adults, and is the only type of milk that should be consumed by people on strict low-fat diets. Unfortunately, skim milk has a very "thin" flavor and an unappealing bluish cast
Fresh Milk
Over 50% of the milk produced in India is buffalo milk, and 45% is cow milk.
Buffalo milk has 3.6% protein, 7.4% fat, 5.5% milk sugar, 0.8% ash and 82.7% water whereas cow milk has 3.5% protein, 3.7% fat, 4.9% milk sugar, 0.7% ash and 87% water.
Fresh pasteurized milk is available in packaged form. However, a large part of milk consumed in India is not pasteurized, and is sold in loose form by vendors. Sterilized milk is scarcely available in India.
Packaged milk can be divided according to fat content as follows,Whole (full cream) milk - 6% fatstandardized (toned) milk - 4.5% fatDoubled toned (low fat) milk - 3% fatAnother category of milk, which has a small
market is flavoured milk.
Composition of Milk
The role of milk in nature is to nourish and provide immunological protection for the mammalian young.
Milk has been a food source for humans since prehistoric times; from human, goat, buffalo, sheep, yak, to the focus of this section - domesticated cow milk (genus Bos).
Milk and honey are the only articles of diet whose sole function in nature is food.
It is not surprising, therefore, that the nutritional value of milk is high.
Milk is also a very complex food with over 100,000 different molecular species found.
There are many factors that can affect milk composition such as breed variations (cow to cow variations, herd to herd variations - including management and feed considerations, seasonal variations, and geographic variations). With all this in mind, only an approximate composition of milk can be given:
87.3% water (range of 85.5% - 88.7%)3.9 % milkfat (range of 2.4% - 5.5%)8.8% solids-not-fat (range of 7.9 - 10.0%):protein 3.25% (3/4 casein)lactose 4.6%minerals 0.65% - Ca, P, citrate, Mg, K, Na, Zn, Cl, Fe, Cu,
sulfate, bicarbonate,many others
acids 0.18% - citrate, formate, acetate, lactate, oxalateenzymes - peroxidase, catalase, phosphatase, lipasegases - oxygen, nitrogenvitamins - A, C, D, thiamine, riboflavin, others
Milk Fat
The fat content of milk is of economic importance because milk is sold on the basis of fat.
The main milk lipids are triglycerides which are comprised of a glycerol backbone binding up to three different fatty acids.
The fatty acids are composed of a hydrocarbon chain and a carboxyl group. Saturated fatty acids (no double bonds) make up two thirds of milk fatty acids.
density at 20 C is 915 kg/m3
refractive index (589 nm) is 1.462 which decreases with increasing temperature
solubility of water in fat is 0.14 % at 20 C and increases with increasing temperatures
thermal conductivity is about 0.17 J/ msK at 20 C
specific heat at 40 C is about 2.1 kJ/ kg K
electrical conductivity is < 10/ohm cm
dielectric constant is about 3.1
Physical Properties of Milk fat
At room temperature, the lipids are solids, therefore, are correctly referred to as “fat” as opposed to “oil” which is liquid at room temperature.
The final melting point of milkfat is 37 C. This temperature is significant because 37 C is the body temperature of the cow and the milk would need to liquid at this temperature.
Milk fat provides lubrication. They impart a creamy mouth feel.
The spreadable range of butter fat is 16-24 C. Unfortunately butter is not spreadable at refrigeration
temperatures. Milk fat provides energy (1 g = 9 calories) and
nutrients (essential fatty acids and fat soluble vitamins).
Milk Proteins The primary structure of proteins consists of a polypeptide
chain of amino acids residues joined together by peptide linkages. Amino acids contain both a weakly basic amino group, and a weakly acid carboxyl group both connected to a hydrocarbon chain.
The nitrogen content of milk is distributed among caseins (76 %), whey proteins (18 %), and non-protein nitrogen NPN (6 %).
Precipitation at pH 4.6 – separates caseins from whey nitrogenPrecipitation with sodium acetate and acetic acid (pH 5.0) –
separates total proteins from whey NPN
The casein content of milk represents about 80 % of milk proteins.The distinguishing property of all caseins is their low solubility at pH 4.6.
Most, but not all, of the casein proteins exist in a colloidal particle, known as the casein micelle. Its biological function is to carry large amounts of highly insoluble CaP to mammalian young in liquid form and to form a clot in the stomach for more efficient nutrition. Colloidal calcium phosphate acts as a cement between hundreds or even thousands of submicelles that form the casein micelle. Binding may be covalent or electrostatic.
Lowering the pH leads to dissolution of calcium phosphate until, at pH of 4.6, all phosphate is dissolved and the caseins precipitate. Acidification causes the casein micelles to destabilize or aggregate by decreasing their electric charges. At the same time, the acidity of the medium increases the solubility of minerals so that organic calcium and phosphorus contained in the micelle gradually become souble in the aqueous phase. Casein micelles disintegrate and casein precipitates. Aggregation occurs as a result of entropically driven hydrophobic interactions.
Heat treatment causes the whey proteins to become adsorbed, altering the behavior of the micelle. At temperatures above the boiling point casein micelles will irreversibly aggregate. On heating, the buffer capacity of milk salts change, carbon dioxide is released, organic acids are produced, and tricalcium phosphate and casein phosphate may be precipitated with the release of hydrogen ions.
Whey Proteins The proteins appearing in the supernatant (filtrate) of milk
after precipitation at pH 4.6 are collectively called whey proteins. These globular proteins are more water soluble than caseins and subject to heat denaturation.
Enzymes Enzymes are a group of proteins that have the ability to
catalyze chemical reactions and the speed of such reactions. Some people suffer from lactose intolerance; they lack the lactase enzyme, hence they cannot digest lactose, or dairy products containing lactose.
Vitamins Milk includes fat soluble vitamins A, D, E, and K as well as
several water soluble vitamins (B1, B2, B6, B12) Minerals All 22 minerals considered to be essential to the human diet
are present in milk.
Indian (traditional) Milk Products
There are a large variety of traditional Indian milk products such asMakkhan - unsalted butter.Ghee - butter oil prepared by heat clarification, for longer shelf life.Kheer - a sweet mix of boiled milk, sugar and rice.Basundi - milk and sugar boiled down till it thickens.Rabri - sweetened cream.Dahi - a type of curd.Lassi - curd mixed with water and sugar/ salt.Channa/Paneer - milk mixed with lactic acid to coagulate.Khoa - evaporated milk, used as a base to produce sweet meats.
The market for indigenous based milk food products is difficult to estimate as most of these products are manufactured at home or in small cottage industries catering to local areas.
Buffalo Milk Vs. Cow Milk
No difference in nutritive value: There is practically no difference in the nutritive value and digestibility of milk and milk products obtained from cow and buffalo milks.
Lower cholesterol content: Significantly, cholesterol content of buffalo milk is 0.65 mg/g as compared to the corresponding value of 3.14 mg/g for cow milk.
More proteins: Animal bioassays have shown the Protein Efficiency Ratio (PER) value of buffalo milk proteins to be 2.74 and that of cow milk as 2.49. It will be seen that buffalo milk has about 11.42 per cent higher protein than cow milk.
More important minerals: Buffalo milk is also superior to cow milk in terms of important minerals, namely calcium, iron and phosphorus which are higher by 92 per cent, 37.7 per cent and 118 per cent respectively than those present in cow milk.
More vitamin A: Buffalo metabolizes all the carotein into vitamin A, which is passed on to milk as such.
More viable commercially: Buffalo milk is commercially more viable than cow milk for the manufacture of fat-based and SNF-based milk products, such as butter, ghee and milk powders because of its lower water content and higher fat content.
Most significantly, the lower cholesterol value should make it more popular in the health conscious market.
By the virtue of greater opacity of casein miscelles, coupled with higher levels of colloidal proteins, calcium and phosphorus, buffalo milk is more densely white and has superior whitening properties as compared to cow milk.
Therefore, unlike the cow milk (which is pale-creamish yellow in color) and cow milk fat (which is golden yellow in color), buffalo milk is distinctively whiter.
Buffalo milk is, therefore, more aptly suitable for the production of tea and coffee whiteners than cow milk.
THANK YOU