Nutritive Value of Milk

Newly born infant is unable to ingest and assimilate nutrients from any food source other than milk. Consequently, milk has to provide all the growth, in an easily acceptable form. The nutrients present in milk and milk products are present in the form of carbohydrates, proteins, enzymes, minerals, vitamins, etc., which provide these nutrients in an easy and palatable manner. They not only provide a nutritious diet but also give energy and meet the day to day nutritional needs.

Role of constituents of milk and milk products

•  Growth
•  Supply of energy
•  Maintenance of body
•  Recovery from disease
•  Reproduction
•  Provide taste and appetite and palatability.

Milk and milk products in the form of food not only meet the nutritional requirement but also supplement the above requirements. Apart from birth of the infant these requirements are fulfilled by milk and milk products from growth phase to adult stage.Composition and nutritive value of milk and milk products are given in Table.

Nutritive components in milk and milk products (100 g)

Products like condensed and evaporated milk are also easily digestible which flocculates the protein during heating thus improving digestibility. Likewise, fermented milk products such as dahi, yoghurt, lassi etc., have high therapeutic value because of microbial population which degrade milk components including protein. They also enhance the digestibility of these products.

i. Fat

Lipids are one of the most important constituents of milk. They have an important bearing on the economics of milk and milk products although this picture has changed somewhat due to the importance being ascribed to solids-not-fat also.Nutritive value of milk fat is due to its high calorie value of 9 kilocalories per gram.Second, it serves as a carrier of the fat soluble vitamins A,D,E and K. Milk fat also contains significant amounts of so called essential fatty acids (linoleic and arachidonic acids).

ii. Milk Protein

Milk contains proteins in the form of casein and whey proteins. The amino acids of these proteins are released during digestion in the stomach. These serves as structural building blocks of other body proteins. Our body is able to synthesize some amino acids but others have to be supplied by foods. Twenty amino acids are required by our body for growth and synethesis of proteins. Of the twenty amino acid 10 are not synthesized by our body. They are known as essential amino acids.They have to be supplied through diet. Milk is a rich source of essential amino acids, which comprises tryptophan, phenylalanine, lysine, threonine, valine, methionine,leucine, arginine and histidine.

iii. Carbohydrate

The main carbohydrate of milk is lactose, which is present at a concentration of about 5 percent. Carbohydrate provides energy at the rate of 4.0 kilocalories per gram. Lactose plays an important role as a source of energy. It has other nutritional functions as a sugar enhancing taste of milk and as a sweetener enhancing palatability.

Lactose performs several functions in the body. During intake of lactose through milk it takes a longer time for ingestion than the common carbohydrate cane sugar or sucrose. The increased ingestion time in the stomach favours the growth of desirable bacteria, namely, lactobacillus species preventing undesirable organisms damaging putrefactive in the gastro intestinal tract. Lactose helps in the absorption of calcium by its chelating action. This action of lactose is through the absorption of calcium as calcium lactate.

Lactose intolerance is one undesirable property of lactose in some individuals. During the ingestion of lactose in small intestine it is broken down to glucose and galactose by the enzyme lactase, also called -glycosidase.The enzyme may be destroyed during illness or genetic disorders. This may result in non-breakdown of lactose to its monosaccharides units i.e. glucose and galactose.This defect is known as lactose intolerance. This intolerance can be overcome by either avoiding taking milk or consuming hydrolytic milk products such as dahi,yoghurt, lassi etc.

iv. Vitamins

Milk and its products contain both water soluble and fat-soluble vitamin. Their role is summarized as follow:

1. Vitamin A:Retina of eyes, mucous membrane infection prevention, night blindness, maintenance of good health

2. Aneurin, thiamine (vitamin B 1 ) : Anti beri-beri, polyneuritis, body maintenance

3. Riboflavin (vitamin B 2 ): Oxidation-reduction changes in milk

4. Nicotinic acid: Skin disorder e.g. Pellagra disease

5. Pyridoxine: Anti pellagra factor

6. Biotin: Promotes skin development

7. Folic acid: Prevent pernicious anaemia

8. Vitamin C: Prevent scurvy

9. Vitamin D: Prevention of rickets (bone disease)

10. Vitamin E: Anti sterility

A summary of the distribution of vitamin in milk and dairy products is given in the Table.

Distribution of vitamin in milk and milk products.

v. Minerals
Milk and milk products are a good source of minerals, especially calcium and phosphorus. Our body requires various minerals such as calcium, phosphorus,magnesium, sulphur, nitrogen, sodium, potassium and chlorine (as chloride). There are certain trace elements, which too are needed by individuals in traces. These include iron, copper, zinc, cobalt and iodine.Milk contains calcium and phosphorus in the ratio of 1.3:1 required for optimum growth. This ideal ratio meets the need of a growing child and different individuals with varying age groups.

Except for iron, milk is a good source for trace elements especially zinc, nickel,molybdenum which are considered important for nutrition and proper functioning of certain specific enzyme activities. Milk is an excellent source for calcium and phosphorus. Calcium is an integral part of bones and teeth. Along with phosphorus they are involved in the formation of teeth and bones. Milk meets the entire need of these minerals.

Finally it may be concluded that milk is good source of all the minerals except iron and iodine.