Milk Composition

• Water:  88%

• Carbohydrate: 5%
• Primarily Lactose (disaccharide containing beta-linked Glucose and Galactose)
• Milk has about half as much sugar in it as Cola
• Lactose not as sweet as sucrose
• Lactose is not easily digested by many non-caucasion adults
• Lactase enzyme can be taken as a suppliment to aid lactose digestion
• When bacteria grow in milk (fermentation), lactose becomes lactic acid: sour
• In aged cheese, lactose all fermented to lactic acid
• Thus can be digested by lactose intolerant people

 
• Fat: 3-4% in Whole Milk
• Most Expensive component of milk
• Amount of fat in milk varies with breed
• 48% of Calories
• Carries fat-soluble vitamins and Cholesterol
• 1 cup milk = 33 mg Cholesterol
• 1 cup skim = 4 mg Cholesterol
• Milk Fat separated from Whole Milk at Dairy: Skim Milk
• Milk Fat added back to make 1%, 2% milk
• Fat exists in globules covered by a  membrane composed of lipid, protein, and lecitin
• Fat lighter than water, so globlules rise to the top (creaming)
• Homogenized milk makes emulsion out of large fat globules
• produces many small globules that do not separate out.
 
                  
                      
 
                      

•  Protein: 3-4%
• Balanced amino acids, easy to digest
• Composed of
• Casein Micelles
• Soluble Whey proteins
• Enzymes
• Casein Micelles: 80% of Protein
• Casein molecules aggrigate with each other, calcium and phosphorus to form micelles
• Micelles have a hydrophobic core, and are hydrophilic on the surface
• Cascin is a natural emulsifier: has both hydrophobic and hydrophilic sections
• Cascin Micelles form a colloid in milk: are suspended, not in solution
• Casein can be coagulated by heat, salt or acid
• Casein isoelectric point at pH 4.6: coagulates at this pH
• Acid added to milk curdles milk to make cottage cheese: curds and whey
 
 
                            
 
 
• Soluble Whey Proteins (Serum): 20% of Protein
• Primarily lactalbumins and lactoblobulins
• Whey does not coagulate at pH 4.6
• Requires heat to coagulate
• Enzymes
• Lipase (breaks down lipids)
• Protease (breaks down proteins)
• Alkaline Phosphatase: activity indicates lack of pasteurization
• Vitamins and Minerals
• Good source of both water-soluble and fat soluble vitamins
• Riboflavin (light sensitive)
• Vitamin A (fat soluble): fortified in low-fat milk
• Vitamin D in small amounts naturally: fortified
• Calcium and Phosphorus: 1% of milk
• Calcium combines with casein to form calcium caseinate
• Calcium combines with Phosphorous to form calcium phosphate

• Milk produced from Cows (major production), Goats, Sheep
• Amount of Milkfat and quantity of milk varies with breed
• Holstein produces most milk
• Guernsey and Jersey produce highest milkfat

           Holstein Cow
 


 
 

• Raw milk from cow is contaminated with bacteria
• Must be refrigerated immediately
• Handled in sanitary manner
• Must be pasteurized
• Unpasteruized milk is a source of:
• Tuberculosis
• Diptheria
• Salmonellosis
• Typhoid Fever
• Undulant Fever
• Q Fever
• Listeria
• Unpasteurized milk contains active alkaline phosphatase enzyme
• Alkaline phosphatase destroyed by pasteurization
• Easy test for this enzyme indicates if milk has been pasteurized
• Male calves of little use in dairy herds
• Sometimes raised for veal
 

• Transgenic Cows, Goats, Sheep produce pharmaceutical products in milk
• Gene encoding pharmaceutical product spliced to milk protein DNA regulatory sequence
• Pharmaceutical gene only expressed in milk
• Expressed at very high levels
• Product easy to purify
• Expression in a mammal gives more authentic product than if expressed in bacteria
 
        
        Rosie the Transgenic Cow
        Makes human lactalbumen for formula for premature infants
 

• Pasteruization destroys 95-99% of pathogenic bacteria in milk
• Increases shelf life of refrigerated milk
• Combination of heat and time minimize breakdown of vitamins and proteins

        Pasteurization through heat exchanger plates: first heated then cooled

• Several methods of Pasteurization
• Batch: low temperature (145F), long time (30 minutes)
• Flash: high temperature (212F), short time (0.01 second)
• Ultrapasteurization: 280F for 2 seconds
• Longer shelf life
• Sterilization at ultrahigh temperature (UHT): 280F for 2-6 seconds
• Milk can be packaged aseptically, stored unrefrigerated until opened



            UHT milk is popular worldwide because it is sterile and shelf stable

• Homogenization
• Milk passed through small orifice:
• breaks up large fat globules
• Small fat globules formed
• Homogenization can occur before or after pasteurization
• Fortification
• Usually fortified with Vitamin D (optional)
• Lowfat milk must be fortified with Vitamin A

Milk Products

• Fluid Milk
• FDA regulates:
• percentage of fat
• percentage of Non-Fat Milk Solids (everything but the water and the fat)
• Lactose-Free Milk
• Treated with enzyme lactase to remove lactose



 

• Evaporated Milk
• 60% of the water is removed by evaporation
• Milk is canned and sterilized
• Reconstituted 1:1 with water
• Slightly tan in color due to Millard browning during canning
• Sweetened Condensed Milk
• 60% of the water is removed by evaporation
• 40-45% sugar added
• Milk is canned and pasteruized but not sterilized because sugar helps prevent microbial growth



 

• Dried Milk
• Spray dried to 5% moisture content
• Cream
• High Fat part of milk:
• Light Cream: 18% Fat
• Heavy Cream: 36% Fat
• Half and Half (cream diluted with nonfat milk): 10.5% Fat
• Butter
• Agitation breaks fat globule
• emulsion breaks
• Fat coalesces
• Sweet Cream butter
• Streptococcus diacetyllactis added
• Produces diacetyl, major flavor of butter




• Ice Cream
• Real Ice Cream contains not less than 10% milkfat
• Ice Milk contains less milkfat

• Streptococcus  and Lactobacillus bacteria added
• Ferment lactose to lactic acid
• Lowers pH, causing casein to coagulate



        Streptococcus lactus
 

• Buttermilk
• Lowfat milk with Lactobacillus and Streptococcus lactus bacteria added
• Lactose fermented, milk clotted due to low pH
• Sour Cream
• Light cream with Lactobacillus and Streptococcus lactus bacteria added
• Lactose fermented, cream coagulated due to low pH
• Yogurt
• Milk products with Lactobacillus bulgaricus and Streptococcus thermophilus added
• Lactobacillus acidophilis also sometimes added
• Live cultures help in digestion of lactose for lactose intolerant people



 

• " A product made from curd obtained from the whole, partly skimmed, or skimmed milk of cows, or from milk of other animals, with or without added cream, by coagulating with rennet, lactic acid, or other suitable enzyme or acid, and with or without further treatment of the separated curd by heat or pressure, or by means of ripening ferments, special molds, or seasoning" - FDA



 

• Curd (coagulated casein) is formed using
• Rennet (Rennin, Chymosin)
• Enzyme from lining of calves stomach that cleaves casein to coagulate milk
• Now 70% of Rennet (Chymosin) is from Genetically Engineered microorganisms
• Acid produced by Streptococcus lactus and Lactobacillus bacteria
• Lactose fermentation produces acid which coagulates casein
• Cottage cheese made this way
• Soft Cheeses contain 40-75% water, large fat globules
• Hard Cheeses contain 30-40% water, very tiny fat globules
• Ripening
• may require 2-12 months
• Result of bacteria, yeast, or mold action
• ferment lactose
• break down some fat
• break down some protein to amino acids
• Not Ripened
• Cottage cheese
• Cream cheese
• Bacterial Ripened
• Swiss cheese: holes due to carbon dioxide produced by bacteria
• Chedder
• Parmesan
• Mold Ripened
• Blue cheese
• Camembert
• Brie
• American Cheese
• Contains one or more Ripened Cheeses
• Melted and Pasteurized
• Emulsifier added to allow cheese to withstand heat
• Result: smooth cheese in jar or solidified in square mold

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