《Food Safety and Home Food Preservation》课程教学课件（PPT讲稿）Milk and Milk Products

Chapter 8 Milk and Milk Products

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, water￾soluble vitamins − milk is a colloidal dispersion for proteins and some Ca phosphate − a dilute emulsion for fat globules

Milk • Milk should contain • 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 ◼ 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

Milk ◼ pH of milk: 6.6 at 25oC ◼ 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

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 ◼ 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 - 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 ◼ 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 - 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 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 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