1. Chapter 8 Milk and Milk Products

2. Milk Milk should contain Milk is ... 8.25% milk-solid-not-fat
3.25% milk fat
Milk is ...
a true solution for salts, lactose, water-soluble vitamins
milk is a colloidal dispersion for proteins and some Ca phosphate
a dilute emulsion for fat globules

3. Milk pH of milk: 6.6 at 25oC Freezing Point: slightly lower than water
when heated, pH decreases, H+ are liberated when Ca phosphate precipitates
Freezing Point: slightly lower than water
Lower surface tension than water due to presence of milk fat, protein, free fatty acids, & phospholipids: easy to foam
Components of milk varies with the feed, breed, nutrition & the physiological condition of the cow

4. Nutritional Components of Milk
Water: 87%, aw = 0.993
Proteins: caseins, whey proteins, enzymes
Lipids: mainly triglycerides
Carbohydrates: mainly lactose, also glucose, galactose, & other saccharides
Salts (<1%),
Trace elements,
Vitamins

5. Milk Proteins - Caseins
Phosphoproteins, account for 80% of total milk proteins
Four groups: alfas1-, alfas1, Beta-, & Kappa-caseins
Present in milk as micelles, stabilized by Kappa-caseins & Ca phosphate
Easily precipitated by adding acid to pH

6. Milk Proteins - Caseins
Acid precipitates caseins
Rennin casein: enzyme rennin coagulates caseins, when Kappa-casein is destroyed by rennin (enzyme from the stomach lining of calves), other caseins react with Ca to form a coagulum
Caseinates: salts of caseins, highly soluble, used as emulsifier, binder, thickening, foaming & gelling

7. Milk Proteins - Whey proteins
Not precipitated by acid, but easily denatured by heat (>60C)
Four Fractions: -lactoglobulins (50%), -lactalbumins (25%), serum albumin & immunoglobulins
rich in sulfur-containing amino acids

8. Milk Proteins - Whey proteins
Use of whey protein products:
Dried Whey: puddings, cakes, baked products
Whey protein concentrates: binder in sausage (up to 3.5%)
Ultra Filtered Skim Milk : coffee whiteners
Cheese Whey: animal feed

9. Milk Proteins - Enzymes
Most of the enzymes are inactivated by pasteurization
alkaline phosphatase is an index of adequacy of pasteurization (phosphatase test)
Lipase may cause hydrolytic rancidity in dairy products if it is not deactivated

10. Milk Lipids Triglycerides = 98% of total milk lipids
Other lipids: phospholipids, free fatty acids, sterols, carotenoids, fat-soluble vitamins
Distinctive dairy flavor due to short-chain saturated fatty acids (C4-C10) : butyric (C4:0), caproic (C6:0), caprylic (C8:0), capric acids (C10:0)
Fat content in milk decreases as cow ages
Fat in feed does not appreciably affect fat content of the milk

11. Milk Carbohydrates Mainly lactose (4.8%), small amount glucose
Two forms of lactose: -monohydrate & anhydrous-
Lactose is the source of lactic acid, formed by bacteria as milk sours
As milk is coagulated, lactose is in the whey
Problems associated with lactose
lactose intolerance - lack -D-galactoside galactohydrolase
crystals from condensed milk or ice cream
lumping and caking of dried milk during storage

12. Milk Carbohydrates Use of lactose browning dispersing agent
topping & icing
carrier for flavor
color ingredients
body & viscosity

13. Vitamins Riboflavin Carotene Milk also provides thiamine & niacin
water-soluble, light sensitive
light yellowish & greenish color
Carotene
fat-soluble, yellowish color of milkfat
skim milk is fortified with retinyl palmitate to replace the carotene in milk fat
Milk also provides thiamine & niacin
Vitamin D is added to almost all milk

14. Minerals
Rich in Ca and P
trace elements: Fe, Mg, Mo, Ni, Zn

15. Pasteurization of milk
Heating milk at a definite temp for a definite time to destroy pathogens but not all bacteria
62oC for 30 min
70oC for 15 sec to 100oC for 0.01 sec (HTST)
138oC for 2 sec (UHT)
to inactivate enzymes (lipase), control rancid & oxidized flavor, and increase shelf life

16. Fermentation of Milk All fermented milk contains lactic acid
Undesirable (spoiled products)
Desirable (buttermilk, yogurt, cheese)
streptococcus lactis initiates the process with lactobacilli spp. continuing the fermentation
Increased thickness due to the association of casein micelles, often accompanied by ß-lactoglobulin.

17. Homogenization of Milk
Forces milk through small openings and break up the fat globules.
The fat globule membrane is disrupted as new surfaces are created
Homogenized milk is whiter in color, more viscous, more bland in flavor, and foam easily.
Less heat stable (curdle more readily), form softer curd

18. Drying of Milk Dry milk products whole dry milk powder (WDM)
nonfat dry milk (NFDM)
dry butter milk
dried whey
dry cream
malted milk powder

19. Evaporation & Canning of Milk
Evaporated milk
sterilized canned milk that has been concentrated to about half its original volume by evaporation under a partial vacuum.
25% total milk solids including >7.5% milk fat
high temp canning may give cooked flavor (methyl sulfide)
storage at high temp for long time may develop off-color (Maillard reaction)

20. Evaporation & Canning of Milk
Sweetened condensed milk
15% sugar is added after concentration of whole milk through evaporation
total CHO concentrations of approx. 56% which is sufficient to prevent spoilage by microorganisms

21. Milk Foams
Milk can form gas-in-liquid foams because the milk proteins have
low surface tension - easier to spread the liquid proteins into thin films
low vapor pressure - reduces the evaporation
In fluid milk, the protein concentration is too low to produce a foam with any stability
Foams can be formed in evaporated milk or dried milk solids.

22. Effect of Heat on Milk Products
Scorching
Some of the whey proteins (-lactoglobulin and -lactalbumin) denature and ppt to form a thin layer of protein on the bottom.
This protein gradually undergos the Maillard reaction with lactose, leading to scorching.
Scum formation
denatured protein molecules join together
evaporation of water from the surface (increasing the concentration of casein and salts)

23. Effect of Heat on Milk Products
Casien is quite resistant to ppt when heat is applied, but severe heating can cause it to form a curd at pH 7.