1. The Biochemistry of Milk – PRE LAB NOTES

2. Complex Nature of Milk 87% water Contains over 250 different compounds
Lactose (milk sugar)
Water soluble vitamins
Trace minerals
Fat. Proteins, carbohydrates

3. Protein
Two main proteins:
Casein (80%)
Whey (20%)

4. Casein Stability (pH)
Casein loses stability when pH drops to 4.6 or lower (more acidic)
Casein denatures and forms lumps – coagulation – called curds or clots.
When cooking with milk, add starch or flour – the carbohydrate surrounds the casein molecules and prevents coagulation.
Higher fat creams show smaller curds because fat also coats casein molecules.
Casein curds are the basis for many cheeses.

5. Whey Whey is the clear liquid left behind after casein coagulates.
Stable in presence of acids, but easily coagulated in presence of heat.
Can be dried into a powder to be sold as a protein nutritional supplement.

6. Fat Fat is dispersed throughout the milk / cream.
Cream is milk that is extra-rich in fat droplets.
Milk and cream are classified as emulsions. An emulsion is a mixture of two or more liquids that are normally immiscible (like oil and water).
Fats in cow’s milk are the most complex fats known.
Contain over 400 different fatty acids
Contains cholesterol (LDL)

7. Carbohydrates Lactose (milk sugar) Digested by enzyme lactase.
Lactose intolerance:
Missing enzyme lactase
Lactose is metabolized by bacteria in intestines
Produces acids and gas that cause symptoms bloating, cramps, and diarrhea.
Treatment – limit milk products, use cultured products like yogurt, drink lactose-free milk, or eat lactase supplements to supply missing lactase.

8. Minerals and Vitamins Mineral salts help prevent curdling
Minerals include calcium and trace amounts of cobalt, copper, iodine, magnesium, nickel, molybdenum.
Vitamins include riboflavin, thiamin, niacin, vitamin A.

9. Milk Processing Milk is processed for: Shelf-life and stability
Fat content
Fortification of vitamins and minerals

10. Pasteurization Louis Pasteur
Milk is heated to a high temperature to kill harmful bacteria
Denatures enzymes that cause milk to spoil – delays spoilage
It is illegal in Canada to sell raw milk

11. Homogenization
Uses pressure to break down large, natural fat molecules into the liquids of milk allowing it to stay blended.

12. Fortification Addition of nutrients to a food
Vitamin D – without vitamin D your body cannot absorb and use calcium very well.
Vitamin A – removing fat removes some vitamin A. By law, processors have to add vitamin A to the milk to make up for the loss.

13. Cheese
Made by coagulating milk protein casein through work of lactic acid bacteria.
Whey is drained, and curds are shaped
Ripening
Physical and chemical changes
Can take many months
Enzymes and bacteria create texture, flavour and appearance
Some cheeses are unripened – mozzarella, cream cheese, cottage cheese