Milk chemistry and composition - Basics for Dairy processing

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

1. INTRODUCTION TO MILK
Dairy processing
Definition, Composition, physical and chemical properties

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
Emulsionofmilkfatglobuleswhichcontainthemilklipids,fat
solublevitamins,andthecomponentsoftheFGM
Colloidalsuspensionofcaseinmicelles(whichcontaincasein
proteins,calcium,phosphate,citrateandwater),globular
proteins,andlipoproteinparticles
Solutionoflactose,solubleproteins,minerals,vitamins,acids,
enzymes,andothercomponents

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

17. Milk composition

18. Relative composition of Dried milk

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)

24. Milk fat

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:
α
S1-casein, α
S2-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 (α
S1-casein and β-
casein)

34. α-Caseins
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.
α
S1-casein α
S2-casein

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 α
S1-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 β1-4 -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