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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 ...
Definition (FDA) 
 Lacteal secretion, practically free from colostrum, obtained by 
the complete milking of one or more h...
Definition (Chemical) 
 Complex chemical substance in which: 
 Fat is present in the form of an emulsion 
 Protein and ...
Description of Milk 
 Emulsion of milk fat globules which contain the milk lipids, fat 
soluble vitamins, and the compone...
Milk secretion 
 All species of mammals secrete milk 
 To provide nutrients required for the optimum growth of the 
new ...
Differences in the composition of milk 
from various species 
 Buffalo and Sheep milk - maximum fat 
 Fat percent in goa...
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 simi...
Colostrum 
 Growth factors 
 Insulin-like growth hormone (IGF) – IGF-I and IGF-II, 
 Transforming growth factor (TGF) 
...
Colostrum 
 Immune factors (Immunoglobulins, Ig, Lactoferrin) 
 For the passive immunization of the newborn 
 Antibacte...
Milk composition
Relative composition of Dried milk
Factors affecting Milk composition 
 Animal factor 
 Genetic, Species, Breed, Individual cow, Lactation period 
 Age & ...
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 Fat 
 In fat globules - protected by a membrane (FGM) 
 Fat globules range from 1 to 20 μm in diameter 
 Made up o...
Milk fat 
 Contain traces of fatty acids; vitamins A, D, E, and K; and 
enzymes. 
 More than 400 different fatty acids 
...
Milk fat
Milk fat 
 Lipids, lipoproteins, cerebrosides, nucleic acids, enzymes, trace 
elements (minerals), and some bound water m...
Milk fat 
 Short free fatty acids situated in the milk plasma are ionized 
and more water-soluble than long free fatty ac...
Milk fat 
 Compound lipids also occur in milk such as phospholipids and 
phosphatides that are situated mainly in the fat...
Milk fat 
 Furthermore, autoxidation of the double fatty acid bonds or 
residues can occur, leading to off flavors. 
 Wh...
Milk Proteins 
 Proteins are made up of amino acids with specific properties 
that are determined by the side chains of t...
Milk Proteins 
 Temperature, ionic strength, and pH affect protein 
conformation. 
 Major classes – Casein, Whey or seru...
Casein Proteins 
 Four main types of casein have genetic variants: 
 αS1-casein, αS2-casein, β- casein, and κ-casein. 
...
Casein Proteins 
 Caseins have distinct disordered molecular structures that lack 
disulfide bridges 
 Very heat stable,...
Casein Proteins 
 Hydrophobicity - counteracted by the 
 high phosphate content 
 low concentrations of sulphur - conta...
α-Caseins 
αS1-casein αS2 - casein 
 199 amino acids and is app. 
23.6 kDa. 
 highest charge of all the 
casein molecule...
β-Casein 
 β-casein consists of 209 amino acids and is approximately 24 
kDa. 
 It is the most hydrophobic casein molecu...
γ-Casein 
 γ-casein is derived by hydrolysis of β-casein by the enzyme 
plasmin. 
 Three variants have been identified n...
Κ - Casein 
 κ - casein consists of 169 amino acids and is approximately 
19 kDa, and it contains both glycosylated and 
...
Casein micelles 
 Casein micelles consist of a large portion (approximately 
95%) of casein proteins that interact with e...
Casein micelles 
 Bovine casein micelles contain 
 water, protein (about 94%), 
 salts (about 6%), including calcium, p...
Whey proteins 
 Whey proteins are hydrophobic, globular, highly ordered 
proteins that contain disulfide linkages. 
 Whe...
Whey proteins 
 The two principal whey proteins in milk 
 α - lactalbumin and β - lactoglobulin 
 Synthesized in the ma...
α-Lactalbumin 
 α-lactalbumin is a spherical, glycosylated compactly folded 
calcium metalloprotein 
 Consists of approx...
β-Lactoglobulin 
 β-lactoglobulin consists of 178 amino acids with an 
approximate molecular weight of 18 kDa. 
 It exis...
β-Lactoglobulin 
 Higher concentrations of β - lactoglobulin are present in 
bovine milk when compared with human milk. 
...
Immunoglobulin 
 Immunoglobulins are antibodies that are synthesized in 
response to specific antigens. 
 They are large...
Immunoglobulin 
 Approximately 0.7 to 1mg/ml is present in bovine milk. 
 The basic structural unit of the immunoglobuli...
Bovine serum albumin 
 Bovine serum albumin consists of 582 amino acids 
 Longest protein. 
 It is approximately 66 kDa...
Proteose peptones 
 Derived from the hydrolysis of β - casein. 
 Considered whey proteins 
 Because elute in the whey f...
Lactoferrin 
 Globular glycoprotein 
 74 kDa and binds to iron (Fe) as it contains two metal binding sites 
 Bovine mil...
Other whey proteins 
 Other minor whey proteins includes 
 growth factors 
 Vitamin - binding proteins 
 Folate, vitam...
Chemical components of 
Bovine milk proteins
Carbohydrates 
 Several carbohydrates in milk: 
 Lactose 
 Glucose 
 Galactose 
 Glycoconjugates (oligosaccharides, g...
Lactose 
 Disaccharide comprised of α / β-D – glucose and β - D - 
galactose that are linked by a β 1-4 - O - glycosidic ...
Lactose 
 β - lactose form has the greatest solubility and is sweeter 
than the α - lactose forms. 
 Major food source f...
Minerals and Salts 
 Milk contains all minerals - essential for human nutrition 
 Including potassium (K), sodium (Na), ...
Minerals 
 Concentrations of calcium, magnesium, ionized phosphate, and 
citrate 
 Depend on the casein content in the m...
Salt 
 If the colloidal equilibrium is destabilized, 
 Concentration of minerals in milk may affect the processing 
 Re...
Salt 
 The primary salts in milk are phosphates, citrates, chlorides, 
sulphates, carbonates and bicarbonates of 
 sodiu...
Milk Enzymes 
 In cow’s milk, ∼20 enzymes have been characterized 
 Another 40 enzymes - demonstrated via their activity...
Milk enzymes 
 Used as indices of 
 Animal health 
 Thermal history of the milk 
 Functions in milk and dairy products...
Milk enzymes 
Enzymes of known or potential technological significance 
 Plasmin 
 Predominant indigenous proteinase in ...
Milk enzymes 
 Lipoprotein lipase 
 Optimal activity at pH 9.2 and 37◦C, relatively heat-labile 
enzyme 
 Initial diges...
Milk enzymes 
 Alkaline phosphatase 
 Optimum activity at pH 9.0–10.5 and ∼37◦ C 
 ALP is relatively heat-sensitive and...
Milk enzymes 
 Sulfhydryl oxidase 
 Catalyzes the oxidation of thiols and the formation of 
disulfide bonds in proteins ...
Milk enzymes 
 Lactoperoxidase 
 relatively heat-stable milk enzyme; heating up to 80◦C 
appears required to ensure ther...
Milk enzymes 
 N-acetyl-p-D-glucosaminidase - activity diagnosed for mastitis 
test 
 Catalase – ass. with somatic cell ...
Milk chemistry and composition - Basics for Dairy processing
Milk chemistry and composition - Basics for Dairy processing
Milk chemistry and composition - Basics for Dairy processing
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Milk chemistry and composition - Basics for Dairy processing

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Presentation on Milk - Definition, composition, factors affecting composition and its components in detail.

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Milk chemistry and composition - Basics for Dairy processing

  1. 1. INTRODUCTION TO MILK Definition, Composition, physical and chemical properties Dairy processing
  2. 2. Topics  Milk: Definition  Composition  Physical and chemical properties  National standards - India
  3. 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. 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. 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. 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. 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
  8. 8. 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
  9. 9. Legal standards for various classes of milk (FSSAI, 2006)
  10. 10. Legal standards for various classes of milk
  11. 11. Legal standards for various classes of milk
  12. 12. 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
  13. 13. 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
  14. 14. 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
  15. 15. Milk composition
  16. 16. Relative composition of Dried milk
  17. 17. 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
  18. 18. Composition(%) of Milk from Dairying species
  19. 19. 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
  20. 20. 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.
  21. 21. 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)
  22. 22. Milk fat
  23. 23. 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
  24. 24. 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.
  25. 25. 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.
  26. 26. 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.
  27. 27. 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.
  28. 28. 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.
  29. 29. 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.
  30. 30. 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%).
  31. 31. 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)
  32. 32. 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.
  33. 33. 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.
  34. 34. 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.
  35. 35. 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.
  36. 36. 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
  37. 37. 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.
  38. 38. 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.
  39. 39. 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
  40. 40. 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.
  41. 41. 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.
  42. 42. 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.
  43. 43. 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.
  44. 44. 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.
  45. 45. 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.
  46. 46. 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
  47. 47. 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.
  48. 48. 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
  49. 49. Chemical components of Bovine milk proteins
  50. 50. 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
  51. 51. 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.
  52. 52. 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.
  53. 53. 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
  54. 54. 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
  55. 55. 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.
  56. 56. 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
  57. 57. 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.
  58. 58. 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
  59. 59. 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
  60. 60. 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
  61. 61. 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
  62. 62. 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
  63. 63. 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
  64. 64. 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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