CHEMICAL COMPOSITION OF MILK

The role of milk and dairy products in nutrition of the population

 

Milk - one of the most valuable products of human nutrition. On nutritional value, it can replace any product, but no one product will not replace milk.

Milk and milk products are widely used in the treatment and prevention of a variety of human diseases. Particular importances are the dairy products for the treatment of diseases of the liver, lungs, gastrointestinal tract, and others.

Milk contains all the necessary substances for human nutrition - protein, fat, carbohydrates, which are found in balanced proportions and easily digested by the body. In addition, it contains many enzymes, vitamins, minerals and other important elements of nutrition necessary for the normal metabolism.

Especially valuable are the proteins of milk. The degree of digestion of milk proteins is 96-98%. Formed as a result breakdown of proteins amino acids are to build the body's cells, enzymes, defense bodies, hormones and so on.. Some amino acids are easily formed in the body from other acids, but there are some that have to do with food (the human body cannot synthesize them). These amino acids (lysine, tryptophan, methionine, phenylalanine, leucine, isoleucine, threonine, valine) are called essential.The content of essential amino acids milk proteins refer to proteins with a high biological value. Particularly rich in essential amino acids are whey proteins of milk.

Great importance in human nutrition is milk fat. Fats are a source of energy and perform multiple functions in the human body. Biological value of fats is determined by the presence of polyunsaturated fatty acids (linoleic, linolenic and arachidonic). These fatty acids are not synthesized in the human body.

Milk fat contains an insufficient amount of polyunsaturated fatty acids. The presence in milk fat, considerable quantities of phospholipids and vitamins (A, D, E) increases its biological value. In addition, milk fat compared with other fats, is better absorbed by the human body. This is facilitated, first, the relatively low melting point of fat (27 - 34°C), and second, finding it in milk in an emulsified condition in the form of small fat globules.

Milk contains valuable carbohydrate - lactose (milk sugar) used by the body as energy source. The flow of lactose into the intestine of the child promotes the development of beneficial microflora, which, forming lactic acid, suppresses putrefactive processes.

Not less valuable mineral components of milk. First of all, it should be noted the high content of salts of calcium and phosphorus, which the body needs for the formation of bone tissue, restore the blood, brain activity, etc. Both elements are in milk is not only very digestible form, but also in well-balanced proportions that allows the body as they digest. About 80% of the daily human need for calcium is met by dairy products.

The milk contains such important macronutrients as potassium, sodium, magnesium, chlorine and micronutrients - zinc, cobalt, manganese, copper, iron, iodine, that are involved in the construction of enzymes, hormones and vitamins.

Milk is almost all types of vitamins. So, the daily requirement of relatively scarce vitamin B2 is satisfied at 42-50% due to milk and dairy products. Also the main source of vitamin A in human nutrition is butter.

Liver - печень

Lung - легкие

Gastrointestinal tract - желудочно-кишечный тракт

Putrefactive - гнилостный

 

Lecture 2

CHEMICAL COMPOSITION OF MILK

2.1 The average chemical composition of cow's milk

Milk is a biological fluid that is formed in the mammary gland of mammals and is intended for feeding the newborn. The simplified average composition of cow's milk is shown in Fig. 1.

Chemical composition of milk not only defines its nutritional and biological value, but also affects the technological processing, the yield and quality of finished products.

The contents of individual components in milk is not constant, it changes depending on stage of lactation, breed of animal, health condition of feed, season, the age, individual characteristics, living conditions, milking equipment, etc.

 

 

 

Fig. 1. The average chemical composition of cow's milk

 

The water in the milk

The water performs a variety of functions and plays an important role in biochemical processes. It is the solvent of organic and inorganic substances. In the aquatic environment are the many reactions of the living organism. In some reactions water participates directly (reactions of hydrolysis, oxidation substances, etc.).

Milk contains on average 88 % of the water (varying from 86 to 89 %).The water, part of the milk and dairy products, heterogeneous physical and chemical properties, and its role varies.

Most of the water of milk (84,5 - 85%) is in a free state, i.e., can participate in biochemical reactions. Free water of milk is a solution of various organic and inorganic substances (sugar, salt, etc.). It can easily be turned into the condition of the ice during freezing, or to remove milk by condensation and drying.

The smaller part (3 - 3.5%) of water is in a bound state. There are 2 forms of communication of water in milk:

1. The adsorption bound water is held by molecular forces near the surface of the colloidal particles (proteins, phospholipids, polysaccharides). When the adsorption of the dipoles of water are placed in several layers around hydrophilic centers of the protein molecule (Fig.2).

 

Fig.2. Scheme of the hydration shell of the protein molecule: 1 - water dipoles; 2 - protein

 

The first layer (oriented stationary water molecules, strongly bound to the protein) is called a hydrate or aqueous shells. Hydration shells of properties depends the stability of protein particles as well as milk fat globules. Subsequent layers of water molecules associated with the protein less stable bonds in properties and it does not differ from the free water.

2. A special form of bound water - chemically bound water. This crystal hydrates water, or water of crystallization. In milk, water of crystallization associated with crystals of milk sugar (С₁₂Н₂₂0₁₁ Н₂0).

Bound water with properties different from free. It does not freeze at low temperatures (below - 40°C), does not dissolve salt and sugar. Bound water cannot be removed from milk by drying. The amount of bound water is usually judged on the hydrophilicity of the proteins, i.e. the ability to bind all of the moisture (the moisture of the first and subsequent layers).

Control questions:

1. What is the average chemical composition of cow's milk?

2. Mass fraction of what components of milk to dairy companies controlled?

3. What is the state water in the milk?