Nutritional Loss Due to Boiling of Milk
Milk is heat-treated at the dairy to kill any pathogenic microorganisms that may be present, without affecting its nutritional quality. But milk boiling (100 degrees Celsius) at home causes changes in its constituents. The higher the temperature and the longer the exposure to heat, the greater the changes. Loss of calcium: The solubility of calcium phosphate of milk is very temperature-dependent. The solubility of calcium phosphate decreases with temperature. This means that heating causes precipitation of calcium phosphate. After cooling the reaction is readily reversible, but after heating to high temperatures the reversibility is more sluggish and incomplete. Loss of protein: Protein (beta-lactoglobulin, commonly known as whey protein) of milk is fairly heat-sensitive. Denaturation, which is an irreversible reaction, begins at 65 degrees Celsius and is almost total when whey proteins are heated to 90 degree Celsius for five minutes. Milk boils at around 100 degrees Celsius. Loss of vitamins: Losses of vitamins is with respect to mainly Vitamin C and some of the Group B vitamins. The loss of Vitamin C as such is generally of minor importance, as milk is not an important source of this vitamin, but it may influence the nutritional value anyway. The breakdown of Vitamin C is connected with that of Vitamin B12 and protects Vitamin B9 (folic acid) from oxidation. To promote its nutritional supplement, a manufacturer cleverly showed in advertisements that loss of nutrients in boiled milk could be made up by addition of its branded product in boiled milk. As a smart consumer, avoid boiling milk and totally avoid reheating so that you can save nutrients and also money spent on supplements.