Biochemistry of Milk

Complex Nature of Milk Milk is a solution, an emulsion, and a colloidal dispersion Normal pH of milk is about % water

Composition of Milk Casein makes up most of milk - When pH is lowered to 4.6, casein breaks down, coagulates, and turns to curds - heat has little effect on coagulating casein

Whey makes up 20% of milk - also called serum protein - heat easily coagulates whey

Fat - milk is an emulsion - Micelles are clusters of molecules that occur within the colloidal dispersion - Globules vary in size and have a thin membrane around them - Milk fat contains very little cholesterol

- Fats influence flavor, texture, and price - More fat usually equates to more costly milk

Minerals & Vitamins - calcium, potassium, magnesium, sodium, thiamin, niacin, vitamin A, riboflavin - one function is to prevent curdling - riboflavin breaks down when exposed to light

Carbohydrate - Lactose (milk sugar) When milk is heated, reacts with amino acids in protein to produce Maillard reaction, turns a golden brown color and slightly caramel flavor

Lactose Intolerance - inability to digest milk due to the absence of the enzyme lactase in intestines

Processing of Milk Pasteurization – heating raw milk to high temps to destroy bacteria, then cooled. Homogenization – breaking up milk fat into smaller globules which disperses them permanently, eliminates creaming Fortification – adding Vitamin D and Vitamin A

Types of Milk Raw - unpasteurized milk straight from the cow Whole – Contains not less than 3.25 % milk fat. Also fortified with vitamin D. Low-fat milk – milk fat removed to bring the levels between 0.5-2%. Vitamin A is added.

Skim milk – milk fat removed to bring the level to less than 0.5%. Fortified with Vitamin A. Ultra High Temperature – allows milk to be stored without refrigeration for 3 months or more if unopened

Concentrated - Evaporated milk: canned whole milk concentrate with 60% of water removed - Sweetened condensed milk: 50% of water is evaporated and sugar is added

Cream - Whipping cream is the fat from whole milk Nonfat dry milk: milk dried to powdered form.

Cultured milk products - Sour cream: cream that has been soured by lactic-acid bacteria

- Yogurt: made by fermenting skimmed milk with special acid- forming bacteria

Buttermilk: made by adding bacteria to milk

Storage of Milk Closed container protects flavor Opaque container protects riboflavin Canned milk: cool, dry place Dry milk: cool dry place Freezing milk changes consistency