Milk

Milk

Milk is the secretion of mammary glands of mammals, its primary natural function being nutrition of the young.

   All species of mammals secrete milk to provide nutrients required for the optimum growth of the new born and Immunity, protecting it from some of the common diseases.

  The development of the young one in all species of mammals is not uniform as such thus composition of  the milk vary depending up on the nutritional needs of the young one.

Definition(legal) 

    Milk is a whole, fresh, clean, lacteal secretion obtained by complete  milking of  one or more healthy milch animal excluding that obtained 15 days before or 5 days after or such periods as may be necessary to render the milk practically colostrum free containing legally prescribed minimum percentage of fat and Solids-not-fat (SNF).

Composition of milk from different animal species

Milk As Human Food

       The perfect composition of milk not only recommends itself for the growing organism, but it is also suited to satisfy the energy and vitamin requirements of the adult system. 

       In India especially, where the menu is principally vegetarian, the fat and the essential vitamin needs are to be made up with milk and milk products. The indispensability of an adequate supply of milk and milk products in the human diet is shown by the fact that those nations are, in general, healthiest whose average consumption of dairy products are greatest. This is further supported by the fact that even in those countries, the poorer classes which consume a lower average of these products tend to be less robust.

Structure of milk                                                                  

 Milk is a complex chemical substance in which Fat is present in the form of an emulsion, Protein and some mineral matter in the colloidal state,Lactose with some minerals and soluble proteins in the form of true solution. Milk is an oil-in-water emulsion.

Milk Fat

      Milk fat mainly available in the form of fat globule that are protected by a membrane called as fat globule membrane. Size of the fat globules range from 1 to 100μm in diameter.     
 Fat globules are largely made up of triglycerides(98%),  phospholipids(0.2 to 1%), sterols (0.2 to 0.4%).

   Phospholipids and proteins are mostly associate with the fat globule membrane. Milk fat contribute to the whitish color of milk.It is the main parameter which use for calculation of cost of milk in India. 

Milk Protein

•       Milk protein is highly digestible, although digestibility can be reduced by processing.         Processing can also lead to  nutrient loss
•       In milk two types of protein are found casein protein and   whey protein. Casein protein is the major protein which is  80% of total protein of bovine milk and where whey    protein is 20% of total protein, but in human milk major  proteins are whey proteins.
•       In milk casein exists as micellar form as casein micelle   which consist water,casein,salts.
•       Casein micelles are built of smaller particles called sub-micelles.
•       And Whey is the liquid obtained after clotting milk either   with rennet and by acidification(souring) to pH 4.6(isoelectric point of casein) and protein found in whey is whey protein.Whey proteins are mainly globular proteins.

Lactose

     Lactose or milk sugar is the distinctive carbohydrate of milk. It is a disaccharide composed of glucose and galactose. Lactose is a reducing sugar. It is in the form of  true solution.

Flavor 

The flavor of fresh milk is fairly bland. The lactose produces some sweetness and the salts some saltiness. Several small molecules present in very small quantities also contribute to flavor. The fat globules are responsible for the creaminess of whole milk.

Nutritional value

Milk is a complete food for the young calf, and it can also provide good nutrition to humans. It contains virtually all nutrients, most of these in significant quantities. However, it is poor in iron and the vitamin C content is not high. It contains no anti-nutritional factors, but it lacks dietary fibre.