Composition of milk

1
Composition nutritive value of milk

• Mohammad Ashraf Paul
• Prof-cum-chief scientist
• Division of Livestock Products Technology
• FVSc AH,SKUAST-Kashmir

2
Milk

• Milk may be defined as the whole, fresh, clean,
  lacteal secretion obtained by the complete
  milking of one or more healthy milch animals,
  excluding that obtained within 15 days before or
  5 days after calving or such periods as may be
  necessary to render the milk practically
  colostrums-free, and containing the minimum
  prescribed percentage of milk fat and milk solid
  not fat

3
Milk

• Milk is considered a near complete single food
  in nature because it contains almost all
  essential nutrients required for growth and
  development in adequate and assimilable forms.
• Considered as chief protective food because it
  has abundant vitamins and minerals especially
  calcium

4
Standards for different classes of milk in India
Class of milk Designation Fat ( min.) SNF ( min.)
Buffalo Milk Raw,Pasteurized,Boiled , Flavoured,Sterilized 5.0-6.0 9.0
Cow Milk -Do- 3.5-4.0 8.5
Goat/Sheep Milk -Do- 3.0-3.5 9.0
Standardized Milk -Do- 4.5 8.5
Recombined Milk -Do- 3.0 8.5
Toned Milk -Do- 3.0 8.5
Double Toned Milk -Do- 1.5 9.0
Skim Milk -Do- 0.5 8.7
5
Composition of Milk from Different Mammalian
Species (per 100 g milk)
Species Protein (g) Fat (g) Carbohydrate (g) Energy (kcal)
Cow 3.2 3.7 4.6 66
Human 1.1 4.2 7.0 72
Buffalo 4.1 9.0 4.8 118
Goat 2.9 3.8 4.7 67
Donkey 1.9 0.6 6.1 38
Mare 2.7 1.6 7.1 55
Sheep 6.7 8.2 4.7 121
Mouse 9.0 13.1 3.0 171
Whale 10.9 42.3 1.3 443
Seal 10.2 49.4 0.1 502
6
Gross composition of milk of various breeds of
cow ()
Breed Body Wt (Kg) Milk Yield (Kg) Fat Protein Lactose Ash Total Solids
Holstein 640 7360 3.54 3.29 4.68 0.72 12.16
Brown Swiss 640 6100 3.99 3.64 4.94 0.74 13.08
Ayrshire 520 5760 3.95 3.48 4.60 0.72 12.77
Guernsey 500 5270 4.72 3.75 4.71 0.76 14.04
Jersey 430 5060 5.13 3.98 4.83 0.77 14.42
Shorthorn 530 5370 4.0 3.32 4.89 0.73 12.90
7
Comparative Production Efficiency

• Holstein

• Jersey

• 12.16 T.S. x 7360 kg/lactation 895 kg of total
  solids produced/lactation
• (140 of her body wt.!)

• 14.42 T.S. x 5060 kg/lactation 730 kg of total
  solids produced/lactation
• (170 of her body wt.!)

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Approximate Composition (Cow)

• Water 87 (85-88)
• Fat 3.9 (2.4-5.5 )
• SNF 8.8 ( 7.9-10.0)
• Protein 3.25
• Lactose 4.6
• Minerals 0.65-0.7 (Ca, P, citrate, Mg , Na ,K,
  Zn,Cl,Fe,Cu,So4,HCo3 )
• Acids -0.18 (citrate, formate,acetate ,lactate
  ,oxalate)
• Enzymes - Peroxides, catalase, phosphatase,
  lipase
• Gases - Oxygen, Nitrogen
• Vitamins- ADEK,C B Vitamins

9
Terms to describe milk fractions

• Milk Plasma (Skim Milk) Milk Fat
• Milk Serum (Whey) Plasma Casein micelles
• SNF Proteins,lactose,minerals,
  acids,enzymes,Vitamins
• TS SNFFat

10
Milk described as

• An oil-in-water emulsion with fat globules
  dispersed in the continuous serum phase
• A Colloidal suspension of casein micelles,
  globular proteins and lipoprotein particles
• A solution of lactose, soluble proteins,
  minerals, vitamins etc.

11
MILK
True fat ( 98 TGs MG DG FFA)
Phospholipids (Lecithin, Cephalin, Sphyngomyelin)
12
Constituents of Milk

• Water
• Water constitutes the medium in which other milk
  constituents are either dissolved or suspended.
• Mostly in free from but some portion also in
  bound form being firmly bound by milk proteins,
  PL etc.

13
Milk Fat/ Lipids

• Structure
• The bulk of the milk fat in milk exists in the
  form of small globules which average 3µm in size
  (0.1-22µm).
• Oil-in-water type of emulsion
• The surface of fat globules is coated with an
  adsorbed layer called fat globule membrane( FGM).
  

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Milk Fat/ Lipids

• FGM contains PL proteins in the form of a
  complex that stabilizes the emulsion (prevents
  fat globules from coalescing separating )
• The emulsion can, however, be broken by
• agitation at low temperatures
• heating
• freezing etc.

15
Creaming

• When milk is held undisturbed- fat globules tend
  to rise to the surface to form a cream layer
• higher fat content , large sized FG - thicker
  cream
• Stokes law (V r2 (d1 - d2) g / 9?) predicts
  that the FG will cream due to differences in
  densities between the fat and plasma phases of
  milk
• however, in cold raw milk, creaming takes place
  faster than is predicated by stoke's law alone

16
Cold Agglutination

• IgM forms a complex with lipoproteins called
  cryoglobulin
• Cryoglobulin precipitates on to the FG and causes
  flocculation (Cold Agglutination)
• As fat globules cluster, the speed of rising
  increases and sweeps up the smaller globules with
  them
• The cream layer thus forms rapidly within 20-30
  min, in cold milk.

17
Milk Lipids (Chemical properties)

• Originate either from microbial activity in rumen
  and transported to secretary cells via blood and
  lymph or synthesized in the secretary cells
• Main lipids in milk are triglycerides
  (glycerol3FA , 98)
• There is a small number of mono, diglycerides and
  FFA in fresh milk which may be due to either
  early lipolysis or incompelete synthesis

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Major Fatty acids in milk

• Long chain

• Short chain

• C14-Myristic 11
• C16-Palmitic 26
• C18-Stearic 10
• C181-Oleic 20

• C4-Butyric
• C6-Caproic
• C8-Caprylic
• C10-Capric

19
Other lipid classes in milk

• Phospholipids (0.8) mainly associated with FGM
• Cholesterol (0.3) mainly located in FG core

20
Lipids of milk
Constituent Range of occurrence Location in milk
Triglycerides 98-99 Fat globules
Phospho lipids 0.2-1.0 Globule membrane and serum
Sterols (Cholesterol, Lansterol) 0.25-0.40 Fat globules, globule membrane and milk serum
Free Fatty Acids Traces Fat globules and milk serum
Waxes Squalene Traces Fat globules
21
Lipids of milk
Constituent Range of occurrence Location in milk
Fat-soluble vitamins Traces Fat globules
Vit. A µg /g fat 7.0-8.5
Carotenoids µg /g fat 8-10
Vit E µg /g fat 2-50
Vit D Traces
Vit K Traces
22
Functional properties

• provides lubrication
• Imparts a creamy mouth feel
• provides unique flavour in butter (low levels of
  SCFA)
• Reservoir for other flavours e.g. in aged cheese
• shortening effect in cheese (keeps protein matrix
  extended to give a soft texture)
• Provides energy _at_ 9 Cal./g.
• Provides nutrients (EFA. Vit.ADEK)

23
Milk Proteins

• Fall into two distinct types
• Caseins
• Whey protein

24
The Concentration of Proteins in Milk
Protein Class g/litre of total proteins
Total Proteins 33 100
Total Caseins 26 79.5
Alpha S1 10 30.6
Alpha S2 2.6 8.0
Beta 9.3 28.4
Kappa 3.3 10.1
25
The Concentration of Proteins in Milk
Protein Class g/litre of total proteins
Total Whey Proteins 6.3 19.3
a-Lactalbumin 1.2 3.7
?-Lactglobulin 3.2 9.8
BSA 0.4 1.2
Immunoglobulins 0.7 2.1
Proteose peptones 0.8 2.4
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Caseins

• Found only in milk
• Caseins constitute about 80 of total proteins in
  milk
• Caseins have five classes
• Alpha S1
• Alpha s2
• Beta
• Kappa
• Gamma (Proteolysis of ß-casein) (lt 5)

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Caseins

• Caseins are resistant to heat denaturation
  because
• Primary structure completely defined
• have a modest size
• Do not possess an organized structure
• Lack tertiary structure disulfide bonds
• Very little structure to unfold

28
Caseins

• Present in colloidal state
• Have low solubility at pH 4.6
• Conjugated proteins (mostly with phosphate
  groups)
• Calcium binding is proportional to phosphate
  content.

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Composition and properties of casein fractions
Fraction Molecular weight Proportion whole caseins Serine-PO 4 residues Calcium sensitivity Carbohydrate
a-s1 23 000 38.1 5-9 -
a-s2 25 000 10.2 10-13 -
ß 24 000 35.7 5 -
? 11600-20500 3.2 0 or 1 - -
? - 12.8 1 -
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Structure

• Caseins are organized into particles
• (100 nm)
• Exist in micelles - porous colloidal particles
• Biological function is to carry caP (insoluble)
  to mammalian young in liquid form for efficient
  nutrition.

31
Structure

• Micelles Contain
• Casein protein
• Calcium
• Phosphate
• Citrate
• Minor ions
• Lipase
• Plasmin
• Entrapped milk serum

32
Micellar frame work

• Alpha s forms the network
• Complexed with caP
• Beta and Kappa caseins accommodated in the Alpha
  S frame work
• Kappa casein also localized on the micelle
  surface - provides stability

33
Rennet Action
34
Whey Proteins

• Milk on precipitation at pH 4.6 yields
  Supernatant (whey proteins )
• Colloidal state
• Globular proteins
• More water soluble than caseins
• Heat denaturable (_at_ gt650C)
• Denaturation increase WHC
• Have good gelling and whipping properties

35
Whey Proteins

• Principal fractions
• ß lactoglobulim, MW- 18,000
• a- lactalbumin, MW-14,000
• BSA
• Immunuglobulin
• Contain sulphur amino acid

36
Nutritional value

• Milk proteins have very high NV
• Score very highly on Provisional scoring pattern
  for quality (UN,FAO)
• Caseins poorer in S aa, WP richer
• But complementary nature of the aa profile of the
  two protein fractions is exceptionally high.
• Milk proteins are complementary to grain and soy
  proteins
• Milk Proteins ideal for fortification of food
  stuffs.
• Protein highly digestible.

37
Lactose

• By weight the most abundant of milk solids
  (4.8-5.2 of milk 52 of SNF,70 of whey solids)
• Exists only in milk in true solution form in milk
  serum
• One-sixth as sweet as sucrose when hydrolyzed by
  ß-D-galactosidase (lactase)-the result is
  increased sweetness and depressed FP
• Disaccharide - one molecule each of glucose and
  galactose.

38
Lactose

• Occurs in two forms alpha and beta which differ
  in their properties
• Alpha form less soluble (7 w/w in water _at_ 150C)
  than beta form
• Equilibrium mixture of both forms has a
  solubility of 17 at 150C
• Used as a fermentation substrate by LAB-the basis
  for the manufacture of fermented/cultured dairy
  products (spoilage microflora-souring)
• Lactose intolerance-absence of lactase

39
Lactose

• Crystallization of lactose occurs in alpha form
  which takes a tomahawk shape-results in a defect
  called sandiness in ice cream and sweetened
  condensed milk.
• In addition to lactose milk contains other CHO in
  small amounts e.g.. Glucose, galactose, OS

40
Lactose

• Nutritional
• Useful source of dietary energy
• Promotes absorption of Ca from the diet

41
Minerals

• Although present in small quantities, exert
  considerable influence on the physico- chemical
  and nutritive profile of milk
• Part of the mineral salts occur in true
  solution, while others are in colloidal state
• All the 22 minerals considered essential to the
  human diet are present in milk.

42
Minerals

• These include 3 families of salts
• Na,K,Cl these free ions are negatively
  correlated to lactose to maintain osmotic
  equilibrium of milk with blood
• Ca,Mg,P(i) citrate (non-diffusible) This
  group consists of 2/3Ca,1/3Mg,1/2P(i) and lt1/10
  citrate in colloidal form present in casein
  micelle.
• Diffusible salts of Ca,Mg, citrate Po4 these
  salts are pH dependant and contribute to overall
  Acid base equilibrium of milk

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THE MINERAL CONTENT OF MILK
Mineral Content per litre
Sodium (mg) 350-900
Potassium (mg) 1100-1700
Chloride (mg) 900-1100
Calcium (mg) 1100-1300
Magnesium (mg) 90-140
Phosphorous (mg) 900-1000
Zinc (µg) 2000-6000
Copper (µg) 100-600
Manganese (µg) 20-50
Iodine (µg) 260
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THE MINERAL CONTENT OF MILK
Mineral Content per litre
Fluoride (µg) 30-220
Selenium (µg) 5-67
Cobalt (µg) 0.5-1.3
Chromium (µg) 8-13
Molybdenum (µg) 18-120
Nickel (µg) 0-50
Silicon (µg) 750-7000
Vanadium (µg) Tr-310
Tin (µg) 40-500
Arsenic (µg) 20-60
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Nutritional value

• Minerals have a high NV.
• Consumption of modest 60 g of SMP provides 75
  RDA for Ca and P
• Dietary ca widely recognized a key factor in
• Healthy bone development in foetus Children.
• Defficiency can lead to the development of
  osteoporosis in post menopausal women.
• Milk is an excellent source of dietary Ca

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Nutritional value

• Its association with phosphorylated caseins
  improves its absorption from the GIT.
• Phosphopeptides released during digestion of
  casein increases the conc. of soluble Ca in the
  intestine ,therefore, enhanced bioavailability
• Milk is also rich in a wide range of elements
• Trace element requirements are contributed by
  milk in the form of Mg, Zn, Se,Mb and I
  significantly.

47
Minor Milk Constituents

• Phospholipids (0.2-1.0)
• Present in FGM Milk serum.
• Three types viz., lecithin, cephalin and
  sphingomyelin
• Lecithin
• forms an imp. Constituent of FGM
• contributes to the richness of flavor of milk and
  other dairy products
• highly sensitive to oxidative deterioration

48
Minor Milk Constituents

• PL are excellent emulsifying agents and serve to
  stabilize milk fat emulsion
• Cholesterol (0.25-0.40)
• In complex formation with proteins in the
  non-fat portion of milk.
• Present as part of the FGM complex in fat
  portion of milk
• Pigments
• Fat soluble- carotene, xanthophyl
• water soluble riboflavin

49
Minor Milk Constituents

• Carotene is responsible for the yellow colour of
  milk, cream, butter, ghee and other fat rich
  dairy products.
• Acts as an antioxidant
• Precursor of Vit.A
• Has two forms alpha and Beta, the former yields
  one while latter two molecules of Vit.A.
• Dairy animals differ in their capacity to
  transfer carotene from feed to milk fat.

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Minor Milk Constituents

• This varies with Species, breed and
  individuality
• Cows in general and some breeds in particular
  (Guernsey, jersey) can transfer more carotene
  from feed to milk fat compared to buffaloes.
• Buffalo milk is whiter in colour
• (carotenoid content 0.25-0.48µg/g vs. cow milk
  30µg/g)
• Riboflavin, besides being a Vit. is a greenish
  yellow pigment- gives characteristic colour to
  whey

51
Minor Milk Constituents

• Enzymes
• Milk is rich in native enzymes
• About 50 different enzyme activities are
  reported- only a small number has significance.
• Lipoprotein Lipase
• Principal lipase in milk
• catalyzes the hydrolysis of TG to FFA
• Present in appreciable quantities in freshly
  drawn milk.

52
Minor Milk Constituents

• Pronounced reactions lead to production of soapy,
  bitter, rancid and unclean flavors
• Spoilage by this enzyme prevented by two factors
• FGM-acts as a physical barrier
• Heat treatment readily destroys lipase

53
Minor Milk Constituents

• Spontaneous lipolysis is rare ,however may occur
  due to factors like ,
• Stage of lactation
• Season
• diet / Plane of nutrition

54
Minor Milk Constituents

• Plasmin
• Major milk proteinase
• Has a trypsin like activity
• Identical to blood plasmin and concentration in
  milk is associated with blood concentration

55
Minor Milk Constituents

• High milk plasmin is seen in conditions like
• Early lactation
• Late lactation
• Udder diseases
• (Leakage of blood components into milk)
• High levels of gamma casein in otherwise
  bacteriologically sound milk is the index of high
  plasimn activity

56
Minor Milk Constituents

• Lactoperoxidase
• Present in high concentrations in milk
• Catalyzes transfer of O2 from H2 O2 to other
  substrates like Thiocyanate
• Has potential to catalyze oxidation of USFA
  leading to development of oxidized flavour

57
Minor Milk Constituents

• Extraneous addition of SCN and H2 o2 in milk
  acts as a powerful bactericide.
• Short term preservation of milk in developing
  countries where refrigeration is scarce.
• Xanthin Oxidase
• Catalyzes Non-Specific oxidation of dairy
  products
• Overall significance is not high.

58
Minor Milk Constituents

• Alkaline Phosphatase
• Completely inactivated by pasteurization
• used as index of efficiency of pasteurization

59
Minor Milk Constituents

• Vitamins
• Essential for many life processes
• Substantial quantities found in milk
• Fat soluble A,D,E,K
• Water soulble B1,B2, B6, B12, niacin,
  pantothenic acid, biotin, folic acid

60
Minor Milk Constituents

• Factors affecting Vitamin concentration
• Seasonal changes
• Breed
• Diet
• Vitamins readily affected by
• Light
• Processing (Deteriorates,A,B2,C)
• Fat soluble stable

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VITAMIN CONTENT OF MILK VITAMIN CONTENT OF MILK
Vitamin Contents per litre
A (µg RE) 400
D (IU) 40
E (µg) 1000
K (µg) 50
B1 (µg) 450
B2 (µg) 1750
Niacin (µg) 900
B6 (µg) 500
Pantothenic acid (µg) 3500
Biotin (µg) 35
Folic acid (µg) 55
B12 (µg) 4.5
C (mg) 20

62
Minor Milk Constituents

• Urea
• Concentration in milk controlled by concentration
  in blood which in turn is controlled by diet.
• Responsible for Seasonal variation in heat
  stability

63
Minor Milk Constituents

• Mechanism by which urea influences heat stability
  
• Urea decompose on heating to yield isocyanate
  which reacts with free SH groups in WP and/or
  Kappa casein
• High levels of urea are associated with very
  stable milk.