Milk Composition I

Composition of 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

Lactose 

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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 sucrose3 whey by driolyzed by B-d-galactosidase (lactose)-the result is increased sweetness and depressed FP Disacchride-onem mole cule each of glucose and galactose.

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Occurs in twso forms alpha and beta which differ in their properties Alpha form less soluble (7% w/w in water @ 150C than betw 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 lactose.

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Crystallization of lactose occurs in alpha form which takes a tomahawk shape-results in a deffect called sandiness in ice cream and sweetened condensed milk. In addition to lactose milk contains other CHO in small amounts eg glucose galactose OS

Nutritional  

Useful source of dietary Promotes absorption of Ca from the diet

Standards for different milks in India S.N Class of milk Designation o

Minimum % Fat % SNF

1

Buffalo milk Raw Pasteurized, 5-6 boiled, flavoured and sterilized

9.0

2 3

Cow Milk -doGoat or sheep domilk

3.5-4.0 8.5 3.0-3.5 9.0

4

Standardized -domilk

4.5

8.5

Minimum S.No Class of milk Designation

% Fat

% SNF

5.

Recombined milk

Raw 3.0 Pasteurized boiled, flavoured and sterilized

8.5

6.

Toned milk

-do-

3.0

8.5

7

Double toned -domilk

1.5

9.0

8.

Skim Milk

Not more than 0.5

8.7

-do-

Composition Percentage composition Name of Water Fat Sps

Protein Lactose

Ash

1 Cow 86.6 (Foreign)

4.6

3.4

4.9

0.7

2. Cow (Zebu)

86.5

4.9

3.2

4.6

0.7

3. Buffalo

84.2

6.6

3.9

5.2

0.8

4. Human

87.7

3.6

1.8

6.8

0.1

Name of Sps

Water

Fat Protein Lactose Ash

Sheep

79.4

8.6 6.7

4.3

1.0

Goat

86.5

4.5 3.5

4.7

0.8

Mare

89.1

1.6 2.7

6.1

0.5

Approx Composition : (Cow)  Water 87 % (85-88%)  Fat 3.9 % (2.4-5.5 %)  SNF 8.8% ( 7.9-10.0%) • • •

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Protein 3.25% Lactose 4.6% Minerals 0.65-0.7% (Ca, P, citrate, Mg ,Na ,K, Zn, Cl,Fe,Cu,So4HCo3) Acids - 0.18% ( citrate, formate, acetate ,lactate oxalate) Enzymes - Peroxides, catalase, phosphates, lipase Gases - Oxygen, Nitrogen Vitamins- ADEK, C&B Vitamins

Terms to describe milk fractions: Whole Milk ↓ Fat SM/Plasma

Plasma = Milk-fat (Skim milk) Serum = Plasma-casein micelles (whey)

↓ Cn micelles

SNF =

Protein, lactose, minerals, acids, enzymes vitamins

Serum/Whey

TS =

Fat + SNF

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.

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MILK________ Total Solids

Water Fat (Lipids)

SNF

Emulsion form (50100 nm dia.) Associated Substance

True fat ( 98% TGs + MG+ DG+ FFA

Phospholipids (Lecithin, Cephalin, Sphyngomylin)

Cholesterol

Carotene

Lactose (solution form, . 01 -1 nm)

Vitamins (A,D,E,K)

Non protein

Caseins (α,β,γ,κ)

β Lactglobulin

α- Lactalbumin

Nitrogen Substance

Mineral matter

Other constituents

PO4, citrates , Chlorides of Na, K, Ca, Mg + traces of Fe, Cu, I etc. •Pigments •Dissolved Gases •Vit. C &B Protein (Suspension, 1-100nm dia.) Complex. •Enzymes •etc Proteose Peptones

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. Milk Fat/ Lipids

Structure 

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The bulk of the milk fat in milk exists in the form of small globules which average 3um in size (0.1-22um). Oil-in-water type of emulsion The surface of fat globules is coated with an adsorbed layer - FGM. FGM contains PL & proteins in the form of a complex that stabilizes the emulsion (prevents fat globules from coalescing & separating ) The emulsion can, however, can be broken by agitation at low temperatures Heating Freezing etc.

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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 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

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IgM forms a complex with lipoproteins k/a cryoglobulin Cryoglobulin ppts. On to the FG and cause flocculation - cold agglutination As fat globules cluster, the speed of rising increases and sweeps up the smaller globules with them The cream layer forms rapidly within 20-30min,. In cold milk.

Milk Lipids Chemical properties  Economic importance – price index  Originate either from microbial activity in rumen and transported to secretary cells via blood and lymph or synthesis in the secretary cells  Main lipids in milk are triglycerides (glycerol+3FA ,98%)  Major Fatty acids in milk:

Long chain C14-Myristic 11% C16-Palmitic 26% C18-Stearic 10% C18:1-Oleic 20%

Short chain C4-Butyric C6-Caproic C8-Caprylic C10-Capric

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There is a small number of mono, diglycerides and FFA in fresh milk which may be due to either early lipolysis or incompelete synthesis other lipid classes in milk Phospholipids (0.8%) mainly associated with FGM Cholesterol (0.3%) mainly located in FG core

Lipids of milk Constituent

Range of Location in milk occurrence

Triglycerides PL (Lec ,ceph, sphing)

98-99% 0.2-1.0%

Sterols (Cholesterol, Lansterol)

0.25-0.40% Fat globules, globule membrane and milk serum

FFA

Traces

Fat globules Globule membrane and serum

Fat globules and milk serum

Waxes

Traces

Fat globules

Squalene

Traces

Fat globules

Fat-soluble vitamins

Tracs

Fat globules

Vit .A

7.0-8.5 ug /g fat

Carotenoids

8-10 ug /g fat

Vit E

2-50 ug /g fat

Vit D

Traces

Vit K

Traces

Functional properties   

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

Milk Proteins  Fall into two distinct types  Caseins  Whey protein

The concentration of proteins in milk : Grams/litre

% of total proteins

Total protein

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

Total whey proteins

6.3

19.3

Alpha lactalbumin 1.2

3.7

Beta lacto globulin 3.2

9.8

BSA

0.4

1.2

Immunoglobulin 0.7

2.1

Proteose peptone 0.8

2.4

Caseins    ~

Found only in milk Caseins constitute about 80% of total protein Caseins have five classes Alpha S1

~

Alpha s2

~

Beta Kappa Gamma (Proteolysis of B-cn.) ( < 5%) Caseins are resistant to heat denaturation because: Primary structure completely defined

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~ ~ ~ ~ • • •

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have a modest size Do not possess an organized structure Lack tertiary structure & disulfide bonds Very little structure to unfold Present in colloidal state Have low solubility at pH 4.6 Conjugated proteins (mostly with phosphate groups) Calcium binding is proportional to phosphate content.

Composition and properties of caseins fraction Fraction

Molecular Proportion Serine- Calcium Carbohyd weight whole PO 4 sensitivity rate caseins % residues

Alpha s1

23 000

38.1

5-9

++

-

Alpha s2

25 000

10.2

10-13

+++

-

Beta

24 000

35.7

5

+

-

Gamma

1160020500

3.2

0 or 1

-

-

12.8

1

-

+

Kappa

Structure  Caseins 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.  Micelles Contain: ~ Casein protein ~ Calcuim ~ Phosphare ~ Citrate ~ Minor ions

~ ~ ~  ~ ~ ~

~

Lipasc Plasmin Entrapped milk scrum 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 surfaceprovides stability

K-cn+ Renent

Cleavage

Eliminates stabilizing ability

At phe 105-Met 106 bond

Hydrophilic Portion K-Cn .Glycomacropeptide(GMP) OR Caseinomacropeptide(CMP)

Hydrophobic portion Para.kappa casein

Whey proteins 

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Milk  pption at pH. 4.6  Supernatant (whey proteins ) Colloidal state Globular proteins more water soluble than caseins Heat denaturable ( @ >650C) Denaturation increase WHC. Have good gelling and whipping properties Principal fractions: B – lactoglobulim, MW- 18,000

Alpha- lactalbumin, MW-14,000  BSA  Ig.  Contain sulphur amino acid Nutritional value.  Milk proteins have very high NV  score very highly on Provisional scoring pattern for quality (UN,FAO)  Caseins poorer in SSA, WP –richer  But complementary nature of the aa profile of the two protein fractions is exceptionally high. 

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Milk protein are complementary to grain and soy proteins Milk Proteins ideal for fortification of food stuffs. Protein highly digestible.

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 B-D-galactosidase (lactase)-the result is increased sweetness and depressed FP  Disacchride-one molecule each of glucose and galactose. 

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Occurs in two forms alpha and beta which differ in their properties Alpha form less soluble (7% w/w in water @ 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

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

Nutritional  

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