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INTRODUCTION TO MILK 
Definition, Composition, physical and chemical properties 
Dairy processing
Topics 
 Milk: Definition 
 Composition 
 Physical and chemical properties 
 National standards - India
Definition (legal) 
 Whole, fresh, clean, lacteal secretions, obtained by complete 
milking of one or more healthy milch animals 
 Excluding that obtained 15 days before or 5 days after or 
such periods as may be necessary to render the milk 
practically colostrum free 
 Containing legally prescribed minimum percentage of fat and 
Solids-not-fat (SNF).
Definition (FDA) 
 Lacteal secretion, practically free from colostrum, obtained by 
the complete milking of one or more healthy cows, 
 May be clarified and may be adjusted by separating part of 
the fat there from; concentrated milk, reconstituted milk, and 
dry whole milk. 
 Water, in a sufficient quantity to reconstitute concentrated and 
dry forms, may be added
Definition (Chemical) 
 Complex chemical substance in which: 
 Fat is present in the form of an emulsion 
 Protein and some mineral matter in the colloidal state 
 Lactose with some minerals and soluble proteins in the form of 
true solution
Description of Milk 
 Emulsion of milk fat globules which contain the milk lipids, fat 
soluble vitamins, and the components of the FGM 
 Colloidal suspension of casein micelles (which contain casein 
proteins, calcium, phosphate, citrate and water), globular 
proteins, and lipoprotein particles 
 Solution of lactose, soluble proteins, minerals, vitamins, acids, 
enzymes, and other components
Milk secretion 
 All species of mammals secrete milk 
 To provide nutrients required for the optimum growth of the 
new born 
 Immunity, protecting it from some of the common diseases. 
 The development of the young one in all species of mammals is 
not uniform as such 
 composition of the milk vary depending up on the nutritional 
needs of the young one
Milk chemistry and composition - Basics for Dairy processing
Differences in the composition of milk 
from various species 
 Buffalo and Sheep milk - maximum fat 
 Fat percent in goat milk is much similar to cow milk 
 Variation among the protein percent less 
 Human milk: 
 Higher percent of lactose and fat 
 Lesser percent of protein and ash content compared with 
other species. 
 Energy supplied - highest in buffalo and sheep milk 
 Difference less between the milk from the remaining species
Milk chemistry and composition - Basics for Dairy processing
Legal standards for various classes of milk 
(FSSAI, 2006)
Legal standards for various classes of milk
Legal standards for various classes of milk
Colostrum 
 First mammary gland fluid secreted by mammals during the 
first 5-7 days after calving 
 Composition is similar to that of blood and differs 
significantly from milk. 
 Nutrients (proteins, fats, lactose, essential fatty acids and 
amino acids) 
 Non-nutrients (biologically active substances) 
 First food for neonates after the parturition that provides 
them with all necessary nutrients 
 Contains more protein - serum protein
Colostrum 
 Growth factors 
 Insulin-like growth hormone (IGF) – IGF-I and IGF-II, 
 Transforming growth factor (TGF) 
 Epidermal growth factor (EGF) 
 Control the growth and development of gastrointestinal 
tract 
 For the functional maturation of the organism during the 
first days after birth
Colostrum 
 Immune factors (Immunoglobulins, Ig, Lactoferrin) 
 For the passive immunization of the newborn 
 Antibacterial factors passes in the offspring 
 Supports their protection against infections during the first 
days after birth 
 Colostrum composition and its biological value affected by: 
 Rearing technology 
 Nutrition during the pregnancy 
 Health status of cows impact
Milk composition
Relative composition of Dried milk
Factors affecting Milk composition 
 Animal factor 
 Genetic, Species, Breed, Individual cow, Lactation period 
 Age & Genetic factors 
 Breed, species, feed and individuality 
 Stage of lactation, pregnancy, nutritional balance 
 Health status of the cow 
 Oestrus, gestation, presence of mastitic infection 
 Environmental factors 
 Extreme climates, stress, exhaustion, housing 
 Milking technique and milking frequency and stage
Composition(%) of Milk from Dairying species
Water 
 Principal constituent in milk 
 79% to 90%, depending on the species 
 It encompasses all other constituents of milk (total solids) that 
are either dissolved or suspended in it 
 Small amounts of water are hydrated or bound chemically to 
lactose, salt, or protein 
 The water activity in milk is relatively high, 0.993 
 Removal of water increases shelf life – powdered milk 
 Regulations prohibit the addition of water to raw milk
Milk Fat 
 In fat globules - protected by a membrane (FGM) 
 Fat globules range from 1 to 20 μm in diameter 
 Made up of app. 
 98% triglycerides 
 0.2% to 1% phospholipids 
 0.2% to 0.4% sterols 
 Phospholipids and proteins mostly associate with the fat 
globule membrane.
Milk fat 
 Contain traces of fatty acids; vitamins A, D, E, and K; and 
enzymes. 
 More than 400 different fatty acids 
 Predominant fatty acids in bovine milk 
 Myristic acid (C14:0 ) 
 Palmitic acid (C16:0 ) 
 Stearic acid (C18:0 ) 
 Oleic acid (C18:1)
Milk fat
Milk fat 
 Lipids, lipoproteins, cerebrosides, nucleic acids, enzymes, trace 
elements (minerals), and some bound water molecules 
 stabilize and prevent the fat globules from coalescence 
during milk processing and handling. 
 FGM prevents attack from lipases (lipolysis) 
 Or increase in the amount of diglycerides, monoglycerides, 
and free fatty acids in milk 
 Free fatty acids are fairly water - soluble and are situated in 
milk plasma and fat
Milk fat 
 Short free fatty acids situated in the milk plasma are ionized 
and more water-soluble than long free fatty acids ( >C14) 
found in fat and at the oil - water interface. 
 Minerals associated with the fat globule membrane are 
copper (5-25%) and iron (30-60%) 
 Other minerals include cobalt, calcium, sodium, potassium, 
magnesium, manganese, molybdenum, and zinc.
Milk fat 
 Compound lipids also occur in milk such as phospholipids and 
phosphatides that are situated mainly in the fat globule 
membranes but also in the milk plasma, lipoproteins, and milk 
microsomes. 
 Phospholipids and phosphatides are highly surface active and 
polar, and dissolve poorly in both water and oil. 
 Lipids can be crystallized, which affects the fat structure, 
melting range, and rheological properties of milk.
Milk fat 
 Furthermore, autoxidation of the double fatty acid bonds or 
residues can occur, leading to off flavors. 
 Whole milk contains 10 to 20mg/100g cholesterol (3.3% fat). 
 The amount of cholesterol is positively correlated with the 
amount of fat in the product. 
 Cholesterol is located in the fat globule membrane, and 
approximately 10% of the cholesterol is esterified.
Milk Proteins 
 Proteins are made up of amino acids with specific properties 
that are determined by the side chains of the amino acids in 
the polypeptide chain. 
 The conformation of the protein depends on the hydrogen 
bonds, hydrophobic interactions, and salt bridges formed 
between the peptide chains. 
 Regular arrangements include β-sheets and α-helices.
Milk Proteins 
 Temperature, ionic strength, and pH affect protein 
conformation. 
 Major classes – Casein, Whey or serum proteins 
 The proteins are synthesized in the mammary gland, 
 Derived genetically 
 Protein content of milk 
 remains constant 
 with a concentration range of 30 to 35g/kg. 
 influenced by the lactation stage of the cow.
Casein Proteins 
 Four main types of casein have genetic variants: 
 αS1-casein, αS2-casein, β- casein, and κ-casein. 
 They are phosphorylated and hydrophobic and associate 
with themselves and each other. 
 They represent 38%, 10%, 36%, and 13% of whole casein 
 Overall, 21 variants of casein have been identified that occur 
by genetic mutations.
Casein Proteins 
 Caseins have distinct disordered molecular structures that lack 
disulfide bridges 
 Very heat stable, withstanding temperatures above 140 ° C 
before dissociating. 
 Their hydrophobicity is due to the 
 high ratios of apolar amino acids 
 including valine, leucine, isoleucine, phenylalanine, and 
proline (between 35% and 45%).
Casein Proteins 
 Hydrophobicity - counteracted by the 
 high phosphate content 
 low concentrations of sulphur - containing amino acids such 
as methionine and cysteine that allow the caseins to be 
reasonably water soluble. 
 Their susceptibility to proteolysis is due to the 
 lack of secondary and tertiary structures (αS1-casein and β- 
casein)
α-Caseins 
αS1-casein αS2 - casein 
 199 amino acids and is app. 
23.6 kDa. 
 highest charge of all the 
casein molecules. 
 Consists of at least eight 
phosphoserine units. 
 It has 17 proline residues that 
ultimately disrupt the 
formation of secondary 
structures, such as α - helices 
and β - sheets. 
 207 amino acids and is app 
25.4 kDa. 
 least hydrophobic casein 
molecule. 
 Several genetic variants, 
contain between 10 and 13 
phosphoserine units. 
 Contains two cysteine 
residues. 
 It exists as a dimer in milk.
β-Casein 
 β-casein consists of 209 amino acids and is approximately 24 
kDa. 
 It is the most hydrophobic casein molecule. 
 There are six known genetic variants that contain between zero 
and five phosphoserine units. 
 Similar to αS1-casein, β-casein has few secondary structures 
due to the presence of 35 proline residues.
γ-Casein 
 γ-casein is derived by hydrolysis of β-casein by the enzyme 
plasmin. 
 Three variants have been identified near the C - terminal end 
of the β-casein molecule.
Κ - Casein 
 κ - casein consists of 169 amino acids and is approximately 
19 kDa, and it contains both glycosylated and 
phosphorylated residues. 
 It can exist as a dimer up to a decamer with the subunits held 
together by disulfide linkages. 
 Unlike the other caseins, it is not sensitive to calcium and 
surrounds the micelles, keeping them intact. 
 It usually contains one phosphoserine unit; 
 however, genetic variants containing two or three 
phosphoserine units have been identified. 
 Further, nine variants have been identified that demonstrate 
different degrees of glycosylation.
Casein micelles 
 Casein micelles consist of a large portion (approximately 
95%) of casein proteins that interact with each other and 
calcium. 
 They vary in size from 80 to 1,000 nm with an average 
diameter of 150 nm in bovine milk. 
 The micelle sizes of sheep and goat milk are different, and the 
caprine micelles are less heat stable than bovine milk micelles
Casein micelles 
 Bovine casein micelles contain 
 water, protein (about 94%), 
 salts (about 6%), including calcium, phosphorus, magnesium, 
citrate - colloidal calcium phosphate [CCP] 
 other traces of metals, enzymes (lipases, esterases, 
proteases), and milk serum. 
 Casein micelles contain submicelles that range from 12 to 15 
nm in diameter 
 Contain approximately 20 to 25 casein molecules and water 
(2 to 5 g/protein) 
 with some submicelles containing K - casein.
Whey proteins 
 Whey proteins are hydrophobic, globular, highly ordered 
proteins that contain disulfide linkages. 
 Whey proteins have well - developed secondary, tertiary, and 
quaternary structures 
 Poorer heat stability 
 denature at temperatures greater than 75 ° C.
Whey proteins 
 The two principal whey proteins in milk 
 α - lactalbumin and β - lactoglobulin 
 Synthesized in the mammary gland. 
 They constitute approximately 20% and 40% of total whey 
protein in bovine milk 
 Other whey proteins are 
 Proteose peptones 
 Immunoglobulins 
 Serum albumin
α-Lactalbumin 
 α-lactalbumin is a spherical, glycosylated compactly folded 
calcium metalloprotein 
 Consists of approximately 142 amino acids and is 
approximately 14 kDa. 
 It is synthesized and secreted by the mammary gland 
 Contains four disulfide bonds and eight cysteine residues, and 
is rich in tryptophan 
 Three genetic variants have been identified 
 It is the principal protein in human milk.
β-Lactoglobulin 
 β-lactoglobulin consists of 178 amino acids with an 
approximate molecular weight of 18 kDa. 
 It exists in both the monomeric and dimeric form at equilibrium 
in bovine milk; 
 Its association depends on temperature, pH, protein 
concentration, and ionic conditions. 
 The hydrophobic dimeric form linked by one to three disulfide 
bonds is approximately 36 kDa.
β-Lactoglobulin 
 Higher concentrations of β - lactoglobulin are present in 
bovine milk when compared with human milk. 
 Better heat stability than α - lactalbumin due to the 
presence of one free sulphohydryl unit. 
 It contains an open β - barrel enclosing a hydrophobic 
cleft and a single three - turn α - helix. 
 It binds to several hydrophobic molecules including retinol and 
fatty acids via the hydrophobic cleft, which in turn stimulates 
lipase activity.
Immunoglobulin 
 Immunoglobulins are antibodies that are synthesized in 
response to specific antigens. 
 They are large, heterogeneous molecules found in the blood. 
The main immunoglobulins in milk are IgG, IgG2, IgA, and IgM. 
 They provide offspring with protection against pathogenic 
microorganisms and their toxins, and the mammary gland 
against infection.
Immunoglobulin 
 Approximately 0.7 to 1mg/ml is present in bovine milk. 
 The basic structural unit of the immunoglobulins is similar, 
consisting of two heavy and two light chains joined together by 
disulfide bonds. 
 IgG is the main immunoglobulin in milk.
Bovine serum albumin 
 Bovine serum albumin consists of 582 amino acids 
 Longest protein. 
 It is approximately 66 kDa 
 Predominantly composed of α - helices. 
 It makes up approximately 1% to 5% of total whey protein. 
 It is synthesized in the liver and enters the milk via secretory 
cells.
Proteose peptones 
 Derived from the hydrolysis of β - casein. 
 Considered whey proteins 
 Because elute in the whey fraction when isolated from milk 
 Heat stable 
 Acid - soluble proteins 
 Mainly responsible for the foaming of skim milk 
 Inhibit rancidity 
 Have an immunological role
Lactoferrin 
 Globular glycoprotein 
 74 kDa and binds to iron (Fe) as it contains two metal binding sites 
 Bovine milk contains app. 20 to 200 mg/L 
 Human milk contains 2 g/L.
Other whey proteins 
 Other minor whey proteins includes 
 growth factors 
 Vitamin - binding proteins 
 Folate, vitamin D, riboflavin, and vitamin B 12 
 Angiogenins 
 Osteopontin 
 Non - protein nitrogen compounds: 
 Urea, uric acid, creatine, creatinine, and hippuric acid 
 In trace amounts
Chemical components of 
Bovine milk proteins
Milk chemistry and composition - Basics for Dairy processing
Carbohydrates 
 Several carbohydrates in milk: 
 Lactose 
 Glucose 
 Galactose 
 Glycoconjugates (oligosaccharides, glycoproteins, and 
glycoaminoglycans) 
 Main carbohydrate – lactose 
 4-5% of total milk content 
 Glucose, galactose, Oligosaccharides - app. 1 mg/ml
Lactose 
 Disaccharide comprised of α / β-D – glucose and β - D - 
galactose that are linked by a β 1-4 - O - glycosidic bond. 
 Depends on the milk yield and lactation stage of the cow 
 Amount of lactose decreases as the lactation stage advances 
 Lactose exists in three forms: 
 α - lactose monohydrate 
 β - lactose 
 Anhydrous α - lactose.
Lactose 
 β - lactose form has the greatest solubility and is sweeter 
than the α - lactose forms. 
 Major food source for bacteria during the fermentation of 
milk. 
 The bacteria hydrolyse the milk into glucose and galactose 
 to produce lactic acid, which inhibits the growth of most 
other microorganisms.
Minerals and Salts 
 Milk contains all minerals - essential for human nutrition 
 Including potassium (K), sodium (Na), calcium (Ca), magnesium 
(Mg), chloride (Cl), and phosphate esters 
 Make up between 0.7% and 0.8% of total milk content. 
 Sodium, potassium, and chloride as free ions 
 readily diffusible 
 Their concentrations are negatively correlated with lactose
Minerals 
 Concentrations of calcium, magnesium, ionized phosphate, and 
citrate 
 Depend on the casein content in the milk 
 Concentration of citrate varies depending on season and diet 
of the cow 
 Affect the soluble calcium content and milk stability 
 Equilibrium between colloidal dispersion and salts
Salt 
 If the colloidal equilibrium is destabilized, 
 Concentration of minerals in milk may affect the processing 
 Require the addition of anions to bind to ionic calcium that 
would restabilize the caseins against aggregation. 
 Salt is added as an additive in certain dairy products 
 The concentration of calcium in milk is relatively high 
 Milk - considered to be an important source of calcium.
Salt 
 The primary salts in milk are phosphates, citrates, chlorides, 
sulphates, carbonates and bicarbonates of 
 sodium, potassium, calcium and magnesium. 
 Since milk contains organic and inorganic salts, 
 Level of salts is not equivalent to the level of mineral 
substances 
 Level of salts is by no means equivalent to the ash content. 
 Factors influencing salt composition: 
 Species, Breed of species 
 Stage of lactation and feed
Milk Enzymes 
 In cow’s milk, ∼20 enzymes have been characterized 
 Another 40 enzymes - demonstrated via their activity. 
 Indigenous milk enzymes are found in, or associated with 
 Casein micelles 
 Milk fat globule membrane 
 Milk serum or somatic cells 
 May originate from blood, somatic cells, the MFGM or the cell 
cytoplasm.
Milk enzymes 
 Used as indices of 
 Animal health 
 Thermal history of the milk 
 Functions in milk and dairy products: 
 Result in quality deterioration 
 Induce desirable changes 
 May also offer protective effects
Milk enzymes 
Enzymes of known or potential technological significance 
 Plasmin 
 Predominant indigenous proteinase in milk. 
 Optimally active at pH ∼7.5 and ∼37◦C 
 Plasmin and plasminogen originate from the mammal’s 
blood and are predominantly associated with the casein 
micelle in milk 
 Cheese ripening and the stability of casein micelles in UHT 
milk
Milk enzymes 
 Lipoprotein lipase 
 Optimal activity at pH 9.2 and 37◦C, relatively heat-labile 
enzyme 
 Initial digestion and absorption of milk lipids in the intestinal 
tract and flavor development in certain cheeses from raw 
milk 
 Lipolysis - development of hydrolytic rancidity in milk
Milk enzymes 
 Alkaline phosphatase 
 Optimum activity at pH 9.0–10.5 and ∼37◦ C 
 ALP is relatively heat-sensitive and its thermal stability is 
only slightly higher than that of non-spore forming 
pathogenic bacteria 
 Indicator of pasteurization efficiency 
 The enzyme's heat-stability profile closely follows that 
necessary for adequate pasteurization
Milk enzymes 
 Sulfhydryl oxidase 
 Catalyzes the oxidation of thiols and the formation of 
disulfide bonds in proteins and peptides. 
 Sulfhydryl oxidase- treated UHT milk may have longer 
flavor stability due to reduced lipid oxidation
Milk enzymes 
 Lactoperoxidase 
 relatively heat-stable milk enzyme; heating up to 80◦C 
appears required to ensure thermal inactivation. 
 anti bacterial agent 
 pH optimum of ∼8.0, and exists primarily in the milk serum
Milk enzymes 
 N-acetyl-p-D-glucosaminidase - activity diagnosed for mastitis 
test 
 Catalase – ass. with somatic cell membrane 
 Xanthine oxidase - contains all of the molybdenum in milk 
 Superoxide dismutase - Protective effect on lipid oxidation 
 γ- Glutamyltransferase - Transport of amino acids into 
mammary gland 
 Lactose synthase – synthesis of Lactose

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Milk chemistry and composition - Basics for Dairy processing

  • 1. INTRODUCTION TO MILK Definition, Composition, physical and chemical properties Dairy processing
  • 2. Topics  Milk: Definition  Composition  Physical and chemical properties  National standards - India
  • 3. Definition (legal)  Whole, fresh, clean, lacteal secretions, obtained by complete milking of one or more healthy milch animals  Excluding that obtained 15 days before or 5 days after or such periods as may be necessary to render the milk practically colostrum free  Containing legally prescribed minimum percentage of fat and Solids-not-fat (SNF).
  • 4. Definition (FDA)  Lacteal secretion, practically free from colostrum, obtained by the complete milking of one or more healthy cows,  May be clarified and may be adjusted by separating part of the fat there from; concentrated milk, reconstituted milk, and dry whole milk.  Water, in a sufficient quantity to reconstitute concentrated and dry forms, may be added
  • 5. Definition (Chemical)  Complex chemical substance in which:  Fat is present in the form of an emulsion  Protein and some mineral matter in the colloidal state  Lactose with some minerals and soluble proteins in the form of true solution
  • 6. Description of Milk  Emulsion of milk fat globules which contain the milk lipids, fat soluble vitamins, and the components of the FGM  Colloidal suspension of casein micelles (which contain casein proteins, calcium, phosphate, citrate and water), globular proteins, and lipoprotein particles  Solution of lactose, soluble proteins, minerals, vitamins, acids, enzymes, and other components
  • 7. Milk secretion  All species of mammals secrete milk  To provide nutrients required for the optimum growth of the new born  Immunity, protecting it from some of the common diseases.  The development of the young one in all species of mammals is not uniform as such  composition of the milk vary depending up on the nutritional needs of the young one
  • 9. Differences in the composition of milk from various species  Buffalo and Sheep milk - maximum fat  Fat percent in goat milk is much similar to cow milk  Variation among the protein percent less  Human milk:  Higher percent of lactose and fat  Lesser percent of protein and ash content compared with other species.  Energy supplied - highest in buffalo and sheep milk  Difference less between the milk from the remaining species
  • 11. Legal standards for various classes of milk (FSSAI, 2006)
  • 12. Legal standards for various classes of milk
  • 13. Legal standards for various classes of milk
  • 14. Colostrum  First mammary gland fluid secreted by mammals during the first 5-7 days after calving  Composition is similar to that of blood and differs significantly from milk.  Nutrients (proteins, fats, lactose, essential fatty acids and amino acids)  Non-nutrients (biologically active substances)  First food for neonates after the parturition that provides them with all necessary nutrients  Contains more protein - serum protein
  • 15. Colostrum  Growth factors  Insulin-like growth hormone (IGF) – IGF-I and IGF-II,  Transforming growth factor (TGF)  Epidermal growth factor (EGF)  Control the growth and development of gastrointestinal tract  For the functional maturation of the organism during the first days after birth
  • 16. Colostrum  Immune factors (Immunoglobulins, Ig, Lactoferrin)  For the passive immunization of the newborn  Antibacterial factors passes in the offspring  Supports their protection against infections during the first days after birth  Colostrum composition and its biological value affected by:  Rearing technology  Nutrition during the pregnancy  Health status of cows impact
  • 19. Factors affecting Milk composition  Animal factor  Genetic, Species, Breed, Individual cow, Lactation period  Age & Genetic factors  Breed, species, feed and individuality  Stage of lactation, pregnancy, nutritional balance  Health status of the cow  Oestrus, gestation, presence of mastitic infection  Environmental factors  Extreme climates, stress, exhaustion, housing  Milking technique and milking frequency and stage
  • 20. Composition(%) of Milk from Dairying species
  • 21. Water  Principal constituent in milk  79% to 90%, depending on the species  It encompasses all other constituents of milk (total solids) that are either dissolved or suspended in it  Small amounts of water are hydrated or bound chemically to lactose, salt, or protein  The water activity in milk is relatively high, 0.993  Removal of water increases shelf life – powdered milk  Regulations prohibit the addition of water to raw milk
  • 22. Milk Fat  In fat globules - protected by a membrane (FGM)  Fat globules range from 1 to 20 μm in diameter  Made up of app.  98% triglycerides  0.2% to 1% phospholipids  0.2% to 0.4% sterols  Phospholipids and proteins mostly associate with the fat globule membrane.
  • 23. Milk fat  Contain traces of fatty acids; vitamins A, D, E, and K; and enzymes.  More than 400 different fatty acids  Predominant fatty acids in bovine milk  Myristic acid (C14:0 )  Palmitic acid (C16:0 )  Stearic acid (C18:0 )  Oleic acid (C18:1)
  • 25. Milk fat  Lipids, lipoproteins, cerebrosides, nucleic acids, enzymes, trace elements (minerals), and some bound water molecules  stabilize and prevent the fat globules from coalescence during milk processing and handling.  FGM prevents attack from lipases (lipolysis)  Or increase in the amount of diglycerides, monoglycerides, and free fatty acids in milk  Free fatty acids are fairly water - soluble and are situated in milk plasma and fat
  • 26. Milk fat  Short free fatty acids situated in the milk plasma are ionized and more water-soluble than long free fatty acids ( >C14) found in fat and at the oil - water interface.  Minerals associated with the fat globule membrane are copper (5-25%) and iron (30-60%)  Other minerals include cobalt, calcium, sodium, potassium, magnesium, manganese, molybdenum, and zinc.
  • 27. Milk fat  Compound lipids also occur in milk such as phospholipids and phosphatides that are situated mainly in the fat globule membranes but also in the milk plasma, lipoproteins, and milk microsomes.  Phospholipids and phosphatides are highly surface active and polar, and dissolve poorly in both water and oil.  Lipids can be crystallized, which affects the fat structure, melting range, and rheological properties of milk.
  • 28. Milk fat  Furthermore, autoxidation of the double fatty acid bonds or residues can occur, leading to off flavors.  Whole milk contains 10 to 20mg/100g cholesterol (3.3% fat).  The amount of cholesterol is positively correlated with the amount of fat in the product.  Cholesterol is located in the fat globule membrane, and approximately 10% of the cholesterol is esterified.
  • 29. Milk Proteins  Proteins are made up of amino acids with specific properties that are determined by the side chains of the amino acids in the polypeptide chain.  The conformation of the protein depends on the hydrogen bonds, hydrophobic interactions, and salt bridges formed between the peptide chains.  Regular arrangements include β-sheets and α-helices.
  • 30. Milk Proteins  Temperature, ionic strength, and pH affect protein conformation.  Major classes – Casein, Whey or serum proteins  The proteins are synthesized in the mammary gland,  Derived genetically  Protein content of milk  remains constant  with a concentration range of 30 to 35g/kg.  influenced by the lactation stage of the cow.
  • 31. Casein Proteins  Four main types of casein have genetic variants:  αS1-casein, αS2-casein, β- casein, and κ-casein.  They are phosphorylated and hydrophobic and associate with themselves and each other.  They represent 38%, 10%, 36%, and 13% of whole casein  Overall, 21 variants of casein have been identified that occur by genetic mutations.
  • 32. Casein Proteins  Caseins have distinct disordered molecular structures that lack disulfide bridges  Very heat stable, withstanding temperatures above 140 ° C before dissociating.  Their hydrophobicity is due to the  high ratios of apolar amino acids  including valine, leucine, isoleucine, phenylalanine, and proline (between 35% and 45%).
  • 33. Casein Proteins  Hydrophobicity - counteracted by the  high phosphate content  low concentrations of sulphur - containing amino acids such as methionine and cysteine that allow the caseins to be reasonably water soluble.  Their susceptibility to proteolysis is due to the  lack of secondary and tertiary structures (αS1-casein and β- casein)
  • 34. α-Caseins αS1-casein αS2 - casein  199 amino acids and is app. 23.6 kDa.  highest charge of all the casein molecules.  Consists of at least eight phosphoserine units.  It has 17 proline residues that ultimately disrupt the formation of secondary structures, such as α - helices and β - sheets.  207 amino acids and is app 25.4 kDa.  least hydrophobic casein molecule.  Several genetic variants, contain between 10 and 13 phosphoserine units.  Contains two cysteine residues.  It exists as a dimer in milk.
  • 35. β-Casein  β-casein consists of 209 amino acids and is approximately 24 kDa.  It is the most hydrophobic casein molecule.  There are six known genetic variants that contain between zero and five phosphoserine units.  Similar to αS1-casein, β-casein has few secondary structures due to the presence of 35 proline residues.
  • 36. γ-Casein  γ-casein is derived by hydrolysis of β-casein by the enzyme plasmin.  Three variants have been identified near the C - terminal end of the β-casein molecule.
  • 37. Κ - Casein  κ - casein consists of 169 amino acids and is approximately 19 kDa, and it contains both glycosylated and phosphorylated residues.  It can exist as a dimer up to a decamer with the subunits held together by disulfide linkages.  Unlike the other caseins, it is not sensitive to calcium and surrounds the micelles, keeping them intact.  It usually contains one phosphoserine unit;  however, genetic variants containing two or three phosphoserine units have been identified.  Further, nine variants have been identified that demonstrate different degrees of glycosylation.
  • 38. Casein micelles  Casein micelles consist of a large portion (approximately 95%) of casein proteins that interact with each other and calcium.  They vary in size from 80 to 1,000 nm with an average diameter of 150 nm in bovine milk.  The micelle sizes of sheep and goat milk are different, and the caprine micelles are less heat stable than bovine milk micelles
  • 39. Casein micelles  Bovine casein micelles contain  water, protein (about 94%),  salts (about 6%), including calcium, phosphorus, magnesium, citrate - colloidal calcium phosphate [CCP]  other traces of metals, enzymes (lipases, esterases, proteases), and milk serum.  Casein micelles contain submicelles that range from 12 to 15 nm in diameter  Contain approximately 20 to 25 casein molecules and water (2 to 5 g/protein)  with some submicelles containing K - casein.
  • 40. Whey proteins  Whey proteins are hydrophobic, globular, highly ordered proteins that contain disulfide linkages.  Whey proteins have well - developed secondary, tertiary, and quaternary structures  Poorer heat stability  denature at temperatures greater than 75 ° C.
  • 41. Whey proteins  The two principal whey proteins in milk  α - lactalbumin and β - lactoglobulin  Synthesized in the mammary gland.  They constitute approximately 20% and 40% of total whey protein in bovine milk  Other whey proteins are  Proteose peptones  Immunoglobulins  Serum albumin
  • 42. α-Lactalbumin  α-lactalbumin is a spherical, glycosylated compactly folded calcium metalloprotein  Consists of approximately 142 amino acids and is approximately 14 kDa.  It is synthesized and secreted by the mammary gland  Contains four disulfide bonds and eight cysteine residues, and is rich in tryptophan  Three genetic variants have been identified  It is the principal protein in human milk.
  • 43. β-Lactoglobulin  β-lactoglobulin consists of 178 amino acids with an approximate molecular weight of 18 kDa.  It exists in both the monomeric and dimeric form at equilibrium in bovine milk;  Its association depends on temperature, pH, protein concentration, and ionic conditions.  The hydrophobic dimeric form linked by one to three disulfide bonds is approximately 36 kDa.
  • 44. β-Lactoglobulin  Higher concentrations of β - lactoglobulin are present in bovine milk when compared with human milk.  Better heat stability than α - lactalbumin due to the presence of one free sulphohydryl unit.  It contains an open β - barrel enclosing a hydrophobic cleft and a single three - turn α - helix.  It binds to several hydrophobic molecules including retinol and fatty acids via the hydrophobic cleft, which in turn stimulates lipase activity.
  • 45. Immunoglobulin  Immunoglobulins are antibodies that are synthesized in response to specific antigens.  They are large, heterogeneous molecules found in the blood. The main immunoglobulins in milk are IgG, IgG2, IgA, and IgM.  They provide offspring with protection against pathogenic microorganisms and their toxins, and the mammary gland against infection.
  • 46. Immunoglobulin  Approximately 0.7 to 1mg/ml is present in bovine milk.  The basic structural unit of the immunoglobulins is similar, consisting of two heavy and two light chains joined together by disulfide bonds.  IgG is the main immunoglobulin in milk.
  • 47. Bovine serum albumin  Bovine serum albumin consists of 582 amino acids  Longest protein.  It is approximately 66 kDa  Predominantly composed of α - helices.  It makes up approximately 1% to 5% of total whey protein.  It is synthesized in the liver and enters the milk via secretory cells.
  • 48. Proteose peptones  Derived from the hydrolysis of β - casein.  Considered whey proteins  Because elute in the whey fraction when isolated from milk  Heat stable  Acid - soluble proteins  Mainly responsible for the foaming of skim milk  Inhibit rancidity  Have an immunological role
  • 49. Lactoferrin  Globular glycoprotein  74 kDa and binds to iron (Fe) as it contains two metal binding sites  Bovine milk contains app. 20 to 200 mg/L  Human milk contains 2 g/L.
  • 50. Other whey proteins  Other minor whey proteins includes  growth factors  Vitamin - binding proteins  Folate, vitamin D, riboflavin, and vitamin B 12  Angiogenins  Osteopontin  Non - protein nitrogen compounds:  Urea, uric acid, creatine, creatinine, and hippuric acid  In trace amounts
  • 51. Chemical components of Bovine milk proteins
  • 53. Carbohydrates  Several carbohydrates in milk:  Lactose  Glucose  Galactose  Glycoconjugates (oligosaccharides, glycoproteins, and glycoaminoglycans)  Main carbohydrate – lactose  4-5% of total milk content  Glucose, galactose, Oligosaccharides - app. 1 mg/ml
  • 54. Lactose  Disaccharide comprised of α / β-D – glucose and β - D - galactose that are linked by a β 1-4 - O - glycosidic bond.  Depends on the milk yield and lactation stage of the cow  Amount of lactose decreases as the lactation stage advances  Lactose exists in three forms:  α - lactose monohydrate  β - lactose  Anhydrous α - lactose.
  • 55. Lactose  β - lactose form has the greatest solubility and is sweeter than the α - lactose forms.  Major food source for bacteria during the fermentation of milk.  The bacteria hydrolyse the milk into glucose and galactose  to produce lactic acid, which inhibits the growth of most other microorganisms.
  • 56. Minerals and Salts  Milk contains all minerals - essential for human nutrition  Including potassium (K), sodium (Na), calcium (Ca), magnesium (Mg), chloride (Cl), and phosphate esters  Make up between 0.7% and 0.8% of total milk content.  Sodium, potassium, and chloride as free ions  readily diffusible  Their concentrations are negatively correlated with lactose
  • 57. Minerals  Concentrations of calcium, magnesium, ionized phosphate, and citrate  Depend on the casein content in the milk  Concentration of citrate varies depending on season and diet of the cow  Affect the soluble calcium content and milk stability  Equilibrium between colloidal dispersion and salts
  • 58. Salt  If the colloidal equilibrium is destabilized,  Concentration of minerals in milk may affect the processing  Require the addition of anions to bind to ionic calcium that would restabilize the caseins against aggregation.  Salt is added as an additive in certain dairy products  The concentration of calcium in milk is relatively high  Milk - considered to be an important source of calcium.
  • 59. Salt  The primary salts in milk are phosphates, citrates, chlorides, sulphates, carbonates and bicarbonates of  sodium, potassium, calcium and magnesium.  Since milk contains organic and inorganic salts,  Level of salts is not equivalent to the level of mineral substances  Level of salts is by no means equivalent to the ash content.  Factors influencing salt composition:  Species, Breed of species  Stage of lactation and feed
  • 60. Milk Enzymes  In cow’s milk, ∼20 enzymes have been characterized  Another 40 enzymes - demonstrated via their activity.  Indigenous milk enzymes are found in, or associated with  Casein micelles  Milk fat globule membrane  Milk serum or somatic cells  May originate from blood, somatic cells, the MFGM or the cell cytoplasm.
  • 61. Milk enzymes  Used as indices of  Animal health  Thermal history of the milk  Functions in milk and dairy products:  Result in quality deterioration  Induce desirable changes  May also offer protective effects
  • 62. Milk enzymes Enzymes of known or potential technological significance  Plasmin  Predominant indigenous proteinase in milk.  Optimally active at pH ∼7.5 and ∼37◦C  Plasmin and plasminogen originate from the mammal’s blood and are predominantly associated with the casein micelle in milk  Cheese ripening and the stability of casein micelles in UHT milk
  • 63. Milk enzymes  Lipoprotein lipase  Optimal activity at pH 9.2 and 37◦C, relatively heat-labile enzyme  Initial digestion and absorption of milk lipids in the intestinal tract and flavor development in certain cheeses from raw milk  Lipolysis - development of hydrolytic rancidity in milk
  • 64. Milk enzymes  Alkaline phosphatase  Optimum activity at pH 9.0–10.5 and ∼37◦ C  ALP is relatively heat-sensitive and its thermal stability is only slightly higher than that of non-spore forming pathogenic bacteria  Indicator of pasteurization efficiency  The enzyme's heat-stability profile closely follows that necessary for adequate pasteurization
  • 65. Milk enzymes  Sulfhydryl oxidase  Catalyzes the oxidation of thiols and the formation of disulfide bonds in proteins and peptides.  Sulfhydryl oxidase- treated UHT milk may have longer flavor stability due to reduced lipid oxidation
  • 66. Milk enzymes  Lactoperoxidase  relatively heat-stable milk enzyme; heating up to 80◦C appears required to ensure thermal inactivation.  anti bacterial agent  pH optimum of ∼8.0, and exists primarily in the milk serum
  • 67. Milk enzymes  N-acetyl-p-D-glucosaminidase - activity diagnosed for mastitis test  Catalase – ass. with somatic cell membrane  Xanthine oxidase - contains all of the molybdenum in milk  Superoxide dismutase - Protective effect on lipid oxidation  γ- Glutamyltransferase - Transport of amino acids into mammary gland  Lactose synthase – synthesis of Lactose