Lactose (milk sugar)

Lactose (milk sugar)
The characteristics carbohydrate of milk is lactose, a disaccharides composed of one molecule of D-glucose and one of D-galactose, which is synthesized in the mammary gland.

The lactose content of cow’s milk is fairly constant, ranging from 4 to 5%. In contrast, milk from cows with mastitis have lactose contents as low as 2.7%.

The more lactose a milk contains, the sweeter its taste. Cow’s milk, with a mean lactose content of 4.6%, tastes faintly sweet.

It is interesting to note that although sweet (nonacid), whey has about the same concentration of lactose as the milk from which it is made, it is much sweeter than milk, due to undoubtedly to the removal of casein.

Lactose in milk is readily fermented by a number of bacteria to yield lactic acid. The changes that accompany the conversion of lactose into lactic acid is associated with the souring of milk. The odor of sour milk is not due to lactic acid but to other volatile products formed during fermentation.

Lactose, in common with other disaccharides, must be hydrolyzed by specific enzymes in the digestive tract into monosaccharide before absorption and utilization by the body.

Lactase the enzyme responsible for the hydrolysis of lactose to D-glucose and D-galactose occurs in the intestinal mucosa of mammals. When lactose intake exceeds the amount that lactose can hydrolyze, symptoms of lactose intolerance (flatulence, cramps, and diarrhea) may ensue.
Lactose (milk sugar)

Definition and Nutritional Values of Milk

Definition and Nutritional Values of Milk
Milk is the normal secretion of the mammary glands for the feeding of the young of mammals. In the United States, the primary milk in this food products rest primarily with the individual states rather than with the federal government. Consequently, legal definitions of milk are not uniform within the United States. The U.S Public Health Service has encouraged the adoption of adequate and uniform state and local control registration. The following definition from its Grade A Pasteurized Milk Ordinance (1965) has been adopted by a majority of the states.

“Milk is hereby defined to be the lacteal secretion, practically free from colostrum, obtained by the complete milking of one or more healthy cows, which contains not less than 8.25% milk solids not fat and not less than 3.25% milk fat.”

The composition of milk is rather complex. Of the major components of milk, the one that most readily distinguishes milk from other foods is lactose, which occurs naturally only in milk. Similarly, casein occurs in milk. The proteins of milk are great importance and contribute essential amino acids necessary for normal health and growth. Milk fat is a palatable mixture of glycerides of fatty acids. The components are in the complex equilibrium, and much is yet to be learned regarding the forms and combinations in which they exist. Lactose and some mineral salts are in the true solutions; the milk proteins as well as some of the calcium phosphate exist in colloidal solution; the fat exists in macroscopic dispersion in the milk plasma. Besides these major constituent, milk contains other constituents such as vitamin, enzymes, pigments and lactic acid.
Definition and Nutritional Values of Milk