1, protein
Cow's milk protein content of 2.8% to 3.3%, mainly by 79.6% of casein, 11.5% of whey (white) protein and 3.3% of the composition of lactoglobulin, and a small amount of other proteins, such as immunoglobulins and enzymes. Where 20 ℃ in pH 4.6 precipitation of cow's milk protein is called casein. Casein is a heat-resistant protein, but can be precipitated in acidic conditions, yogurt and cheese is made on this principle. In milk casein combines with calcium and phosphorus to form casein gels, which are present as a colloidal suspension in buttermilk. Whey proteins are thermally unstable and coagulate and precipitate when heated. Cow's milk protein digestion and absorption rate of 87% to 89%, biological value of 85, is a high-quality protein.
2, fat
Milk fat is about 2.8% to 4.0%, in the form of particles of fat globules dispersed in the emulsion, is a very good emulsification, easy to digest and absorb, the absorption rate of up to 97%. Lipids in buttermilk are mainly triglyceride-based, a small amount of phospholipids and cholesterol, milk fat in the fatty acid composition is complex, oleic acid accounted for 30%, linoleic acid and linolenic acid accounted for 5.3% and 2.1%, respectively, and the short-chain fatty acids (such as butyric acid, has been the acid, octanoic acid) content is higher, about 9%, is the reason that milk fat has a good flavor and easy to digest.
3, carbohydrates
Milk carbohydrates are mainly lactose, cow's milk lactose content of about 3.4% to 5.4%. Lactose in the intestinal tract can promote the absorption of calcium, iron, zinc and other minerals, improve its bioavailability; promote intestinal lactic acid bacteria, especially bifidobacteria reproduction, improve the micro-ecological balance of the human body, and promote intestinal bacterial synthesis of B vitamins. Some people do not drink cow's milk for many years after adulthood, the lactase activity in the body is very low, can not decompose lactose, lactose in the intestine by intestinal microbial decomposition and fermentation, resulting in flatulence, diarrhea and other symptoms, known as lactose intolerance. This part of the population can eat lactase-treated milk powder, or drink yogurt.
4, vitamins
Cow's milk contains almost all kinds of vitamins needed by the human body, and its content is related to feeding methods, seasons, processing methods. Such as grazing period in cow's milk vitamin A, vitamin D, carotene and vitamin C content than winter and spring in the shed feeding increased significantly. Vitamin D content in cow's milk is low, but there is some increase in its content in summer when there is more sunshine. Overall, cow's milk is a good source of B vitamins, providing considerable amounts of riboflavin, vitamin B12, vitamin A, vitamin B6 and pantothenic acid.
5, minerals
Cow's milk mineral content of about 0.7% to 0.75%, rich in calcium, phosphorus, potassium, sulfur, magnesium and other macronutrients and copper, zinc, manganese and other trace elements. 100mL of cow's milk contains 110mg of calcium, three times as much as human milk, and a high rate of absorption, is a good source of calcium. The ratio of calcium and phosphorus in cow's milk is 1.2:1. Cow's milk is also rich in potassium and magnesium, which is good for controlling blood pressure and has become the only alkaline food among animal foods. However, it is low in copper and iron, which must be obtained from other foods.
6, other substances
Milk there are a large number of physiologically active substances, the more important of which are lactoferrin, immunoglobulin, bioactive peptides, *** yoke linoleic acid, tyrosine, hormones, growth factors and a variety of active peptides. Bioactive peptides are produced by protease hydrolysis of milk proteins during digestion, including sedative and tranquilizing peptides, anti-hypertensive peptides, immunomodulatory peptides and antimicrobial peptides. The content of lactoferrin in cow's milk is 20~200ug/mL, which has the function of regulating iron metabolism, promoting growth and antioxidant, etc. The peptide fragments formed by protease hydrolysis have certain immunomodulatory effects.