Chapter 8 Milk and Milk Products

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

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

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

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 5.2-4.6

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

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

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

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

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

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

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

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

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

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

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.

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

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

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)

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

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.

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)

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.