The mammary gland is one of the most important organs in the body of females of all mammals. This gland synthesizes milk, which is the only food product for their babies in the early stages of postnatal development. The mammary gland in animals is often called the udder. The udder of a cow consists of four independent glands. Each gland is divided into lobes (5-20 of them in a cow), each part into lobules. The main structural and functional unit of the gland is the alveolus, which is shrouded in a dense network of capillaries. Milk is a polydisperse system consisting of true and colloidal solutions, suspensions and emulsions. Cow's milk is a white liquid with a yellowish tinge, sweetish in taste and with a peculiar smell.
Milk is synthesized in the alveoli, partly in the small and medium excretory ducts. The resulting secretion enters the large excretory ducts, after which it accumulates in the milk tank. Then it is transported to the nipple canal and is released into the external environment. The mammary gland functions in the lactation period, the duration of which is about 300 days.
Milk is one of the main foods for humans and animals. It consists of proteins, lipids, carbohydrates. Proteins of cow's milk are absorbed by 96-99%, lipids - by 95, carbohydrates - by 98%.
For food, people most often use milk from cows, fewer goats, mares, camels, buffaloes, deer females, zebu and yak.
The chemical composition of milk
Milk contains about two hundred individual substances. These compounds can be divided into five main fractions: salts, water, carbohydrates, lipids, proteins. In milk, water can be in two states: free and bound. When thickening, drying and other types of processing, free water is easily removed. Bound water is part of the solvation shells of polydisperse systems. In fresh milk, the concentration of bound water is about 3.5%, in skim to 2.6%.
The protein composition of milk. The protein concentration in cow's milk can reach up to 4%. Skim milk contains mainly alpha casein. In milk, it forms a caseinate-calcium phosphate complex, which is involved in the formation of the shell of lipid balls; α-lactalbumin is thermostable, participates in the biosynthesis of milk sugar (lactose) from monosaccharides (galactose, glucose); β-lactoglobulin denatures in a neutral environment (pH = 7) and when heated to 70 ° C.
Milk globulins are characterized by a high molecular weight (up to 1 million Yes), a carbohydrate component is included in the structure of their molecules, they exhibit the properties of enzymes (lipoxidases). Non-protein nitrogen compounds in milk are represented by urea and, to a lesser extent, amino acids, purine bases and creatine.
Carbohydrate composition of milk. Most milk carbohydrates are represented by lactose (4.7% on average), monosaccharides (glucose, galactose), amino sugars, and monose phosphoric esters. The highest concentration of lactose is recorded in rhino milk.
The lipid composition of milk. Milk fat contains triacylglycerols, sterols, sterols, phospholipids and glycolipids. Their concentration in animal milk depends on various factors (lactation, breed, diet, etc.). In milk fat there are many residues of stearic, palmitic, myristic and oleic acids.
Vitamin composition of milk. Cow's milk contains a sufficient amount of both fat (A, D, E) and water-soluble (PP, B1, B2, C) vitamins. To increase the concentration of vitamins in milk, animals are fed various diets that are rich in vitamins, and vitamin A, B or E concentrates are also added to the diet: pigments are also contained in milk: carotenes, lactoflavins and chlorophylls, the color of milk depends on their concentration.
One of the disadvantages of milk powder is that it is rather difficult to restore to a liquid state. This product has been produced for more than 110 years, however, the biochemical composition of milk powder is different from its natural state, so natural milk is much more healthy.