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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.

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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

  • 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
Nutritional Componentsof 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
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 caseins6
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
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 proteins8
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
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
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
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 carbohydrates12
Milk Carbohydrates
  • Use of lactose
    • browning
    • dispersing agent
    • topping & icing
    • carrier for flavor
    • color ingredients
    • body & viscosity
  • Riboflavin
    • 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
  • Rich in Ca and P
  • trace elements: Fe, Mg, Mo, Ni, Zn
pasteurization of milk
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
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
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
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
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 milk20
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 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
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 products23
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.