Milk: Meaning, Physical and Physico-Chemical Properties, Constituents, Production, and Trade
Milk
Milk is the secreted fluid of the mammary glands of female mammals. It has almost all of the nutrients needed to keep life going. Goat, sheep, and cow milk have been utilized as food by humans since the beginning of time. The word “milk” is now used interchangeably with cow’s milk. When provided commercially, the milk of other animals is identified, such as goat or sheep milk. Mammals’ mammary glands generate the white liquid meal known as milk. For young mammals, including breastfed human newborns, it serves as their main source of nutrition until they can process solid food. In addition to lactose and saturated fat, milk also includes calcium and protein. Milk immunity is a result of immunological factors and immune-modulating substances in milk.
Physical and Physico-Chemical Properties
1. Milk is an opaque liquid that is white or yellow-white. Protein micelles and milk fat globules scatter and absorb light, which affects the hue.
2. Milk has a pleasantly sweet taste and typically has a very subtle smell and odour.
3. Milk fat is emulsified in milk serum, commonly known as whey, and exists as droplets or globules that are encased in a membrane.
4. Following centrifugation or extended storage, the fat globules, often referred to as cream, separate. On the skim milk, the fat globules float.
5. Milk serum has different-sized proteins. They are known as micelles and are mostly made up of casein molecules’ calcium salts.
6. Milk contains somatic cells, primarily leucocytes (108/l of milk), and lipoprotein particles, also known as milk microsomes, which are made up of the remnants of cell membranes, microvilli, etc.
7. Milk serum dissolves a variety of proteins, carbohydrates, minerals, and other substances.
8. As milk’s fat content rises, its specific density falls, while it rises as its protein, milk sugar, and salt content rise. Cow’s milk has a specific density between 1.029 and 1.039 (15 ◦C).
Constituents of Milk
1. Water: The other ingredients of milk (total solids) are all dissolved or suspended in water. The water percentage in the milk of various cow and buffalo species ranges from 83.18 to 87.2%.
2. Cholesterol: Breed, species, lactation stage, and season all have a noticeable impact on the amount of cholesterol in milk. Generally speaking, western cattle breeds have higher cholesterol levels (317–413 mg/100 g fat), followed by zebu (humped-like Desi) cows (303–385).
3. Casein: Calcium phosphate and casein components combine to form the particles known as casein micelles, which are found in milk. Additionally, a very tiny amount of casein is present in soluble form.
4. Whey Proteins: Whey proteins include immunoglobulins (mostly IgG1, IgG2, and IgM), lactoferrin, protease peptone, serum transferring, glycoprotein, enzymes, and β-lactoglobulin and α-lactalbumin.
5. β – lactoglobulin: The main whey protein found in cow and buffalo milk is β-lactoglobulin.
6. Immunoglobulins (Ig): These are antibodies that are produced in reaction to particular antigens. These provide a general humoral reaction to respiratory and gastrointestinal microorganisms that are Gram-negative. Immunoglobulins fall into five main classes: IgA, IgD, IgE, IgG, and IgM. All Igs share a similar basic structure. Two identical heavy chains (53,000 daltons) and two identical light chains (23,000 daltons) make up these.
7. Lactose: The main carbohydrate in milk, lactose is also referred to as milk sugar. It is a disaccharide containing one D-galactose and one D-glucose residue apiece.
8. Minerals: The average quantity of ash in milk is 0.70 per cent, which corresponds to a salt content of roughly 0.90 per cent. Breed, feed, season, lactation stage, and illness all affect the proportion of salt and ash in milk. The mineral content of milk is determined by measuring the white residue left over after a specific weight of milk is burned.
Minor Constituents
1. Enzymes: A variety of enzymes can be found in milk. In cow’s milk, more than 20 enzymes have been identified and extracted.
2. Alkaline Phosphatase: This enzyme has gained importance due to the connection between the temperature used to pasteurize milk and the temperature at which it becomes inactive.
3. Lipoprotein Lipase: The shelf life of processed milk and milk products is typically shortened by the residual activity of lipase.
Production
Global milk output increased by 1.3% in 2019 to approximately 852 Mt (81% cow milk, 15% buffalo milk, and 4% goat, sheep, and camel milk combined). The world’s largest milk producer, India, had a 4.2% increase in production to 192 Mt, but since India primarily trades small amounts of milk and dairy products, this had little effect on the global dairy market. The three largest dairy exporters—the United States, the European Union, and New Zealand—saw very modest increases in milk production.
According to projections, the world’s milk output would increase at a rate of 1.6% per annum, surpassing that of most other major agricultural commodities, reaching 997 Mt by 2029. The forecast expansion of cowherds (0.8% p.a.) is marginally higher than the estimated average yield growth (0.7%) compared to the previous decade because cowherds are anticipated to grow more quickly in low-yielding countries. Important milk-producing nations India and Pakistan are predicted to contribute more than half of the increase in global milk production over the next ten years, and they will account for more than 30% of global production in 2029.
Trade
International trading accounts for about 8 per cent of global milk production. The main causes of this are milk’s high water content and perishability. During the base period, the US, New Zealand, and the EU were the top three exporters of dairy products. In 2029, it is anticipated that these three nations will collectively produce about 65% of cheese, 68% of WMP, 76% of butter, and 77% of SMP exports.