Chapter 8 Milk and Milk Products Milk Milk

Chapter 8 Milk and Milk Products

Milk · Milk should contain · · · 8. 25% milk-solid-not-fat 3. 25% milk fat Milk is. . . a true solution for salts, lactose, watersoluble vitamins - milk is a colloidal dispersion for proteins and some Ca phosphate - a dilute emulsion for fat globules -

Milk n p. H of milk: 6. 6 at 25 o. C n n when heated, p. H 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

Nutritional Components of Milk Water: 87%, aw = 0. 993 n Proteins: caseins, whey proteins, enzymes n Lipids: mainly triglycerides n Carbohydrates: mainly lactose, also glucose, galactose, & other saccharides n Salts (<1%), n Trace elements, n Vitamins n

Milk Proteins - Caseins Phosphoproteins, account for 80% of total milk proteins n Four groups: alfas 1 -, alfas 1, Beta-, & Kappa-caseins n Present in milk as micelles, stabilized by Kappa-caseins & Ca phosphate n Easily precipitated by adding acid to p. H 5. 2 -4. 6 n

Milk Proteins - Caseins n n n 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

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

Milk Proteins Whey proteins n Use of whey protein products: Dried Whey: puddings, cakes, baked products n Whey protein concentrates: binder in sausage (up to 3. 5%) n Ultra Filtered Skim Milk : coffee whiteners n Cheese Whey: animal feed n

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

Milk Lipids n n n 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 (C 4 -C 10) : butyric (C 4: 0), caproic (C 6: 0), caprylic (C 8: 0), capric acids (C 10: 0) Fat content in milk decreases as cow ages Fat in feed does not appreciably affect fat content of the milk

Milk Carbohydrates n n n 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 n lactose intolerance - lack -D-galactoside galactohydrolase n crystals from condensed milk or ice cream n lumping and caking of dried milk during storage

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

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

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

Pasteurization of milk n Heating milk at a definite temp for a definite time to destroy pathogens but not all bacteria n n 62 o. C for 30 min 70 o. C for 15 sec to 100 o. C for 0. 01 sec (HTST) 138 o. C for 2 sec (UHT) to inactivate enzymes (lipase), control rancid & oxidized flavor, and increase shelf life

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 ßlactoglobulin.

Homogenization of Milk n n 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

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

Evaporation & Canning of Milk n Evaporated milk n sterilized canned milk that has been concentrated to about half its original volume by evaporation under a partial vacuum. n 25% total milk solids including >7. 5% milk fat n high temp canning may give cooked flavor (methyl sulfide) n storage at high temp for long time may develop off-color (Maillard reaction)

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

Milk Foams n Milk can form gas-in-liquid foams because the milk proteins have n n 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.

Effect of Heat on Milk Products n Scorching n n n 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 n n denatured protein molecules join together evaporation of water from the surface (increasing the concentration of casein and salts)

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