Biochemistry of Milk
Complex Nature of Milk
• Milk is a solution, an emulsion, and a
colloidal dispersion
• Normal pH of milk is about 6.6
• 80% 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 acidforming bacteria
• Buttermilk: made by adding bacteria
to milk
Storage of Milk
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Closed container protects flavor
Opaque container protects riboflavin
Canned milk: cool, dry place
Dry milk: cool dry place
Freezing milk changes consistency