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
? 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
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
? 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 ?-
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.
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
? 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
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
? 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 ?-
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.
