milk

Defination 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

MILK

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

Phospholipids(Lecithin, Cephalin,Sphyngomylin)

Water Total Solids

Fat (Lipids)Emulsion form (50-100 nm dia.)

SNF

AssociatedSubstance

Lactose(solution form .01 -1 nm)

NitrogenSubstance

Mineralmatter

Otherconstituents

Cholesterol CaroteneVitamins(A,D,E,K)

Non protein Protein(Suspension, 1-100nm dia.)

Caseins(α,β,γ,κ) α- Lactalbumin β Lactglobulin Proteose Peptones

PO4, citrates , Chlorides of Na, K, Ca, Mg + traces of Fe, Cu, I etc.

•Pigments•Dissolved Gases•Vit. C & B Complex.•Enzymes etc

MILK COMPOSITION

Animals Water

%

Proteins

%

Casein

%

Whey

%

Fat

%

Lactose

%

Ash

%

Human 87.5 1 0.5 0.5 4.5 7.1 0.2

Buffalo 83-84 4 3.5 0.5 6-10 4.8 0.8

Cow 86-87 3.5 2.8 0.7 3.7 4.8 0.7

Goat 86.5 3.6 2.7 0.9 4 4.7 0.8

Sheep 82 4.6 3.9 0.7 7.2 4.8 0.8-0.9

Camel 86.5 3.6 2.7 0.9 4 5 0.5

Horse 88.8 2.5 1.3 1.2 1.9 6.2 0.5

Species

Breed

Stage of lactation

Season

Sanitary state

Feed

Milk : variable compositionMilk : variable composition

micro-organisms

Colloidal suspension Stable emulsion True solution

104 103 102 101 1 10-1

Fat Globules Casein micelles Whey proteins lactose watersoluble minerals

NPN

Forms

Size (nm)

Elements

Casein micelle

Micro-organisms FG

FG

Whey proteins

Different milk phases Different milk phases

milk proteins milk proteins Concentration g/kg %

Total proteins 33.0 100.0

Total caseins 26.0 79.5s1-casein 10.0 30.6

2.6 8.0-casein 9.3 28.4

-casein 3.3 10.1

Whey proteins 6.3 19.3-lactalbumin 1.2 3.7-lactoglobulin 3.2 9.8

Bovine Serum Albumin 0.4 1.2

Immunoglobulins 0.7 2.1

Other (proteoses -peptones) 0.8 2.4

Proteins of fat globule membrane 0.4 1.2

s2-casein

Casein micelle : Casein micelle : Molecules of caseins Molecules of caseins ++ Minerals (calcium phosphate)Minerals (calcium phosphate)

Composition of casein micelles Composition of casein micelles

93 % caseins : 4 phosphoproteins s1-CN : 36 %

s2-CN : 10 % -CN : 34 % -CN : 12 %

7 % : colloidal mineral complex containing phosphate, calcium, magnesium and citrate

Mains models of casein micelles Mains models of casein micelles

Structure with sub-units Open structure

submicelle

Calcium phosphate

Walstra (1990)

Hydrodynamic radius

Hairy layer

Hairy chain

Casein micelles.

• The polymers are built up of hundreds and thousands of individual casien molecules and form a colloidal solution

• These molecular complexes are known as casein micelles.

• Such micelles may be as large as 0.4 microns, and can only be seen under an electron microscope

• A medium-sized micelle consists of about 400 to 500 sub-micelles which are bound together

Casein micelle

• The α- and β-caseins are mainly concentrated

in the middle of the sub-micelles, while κ-casein

predominates on the surface.

• The hydrophilic protruding chain of the κ-casein

protrudes from the surface of the sub-micelles

forming a hairy layer ( 5 – 10 nm).

• The κ-casein-deficient sub-micelles are mainly

located in the centre of the micelle,

Casein micelle

• Whereas the κ-casein-rich sub-micelles

predominate on the surface, giving the whole

micelle a hairy surface layer.

• The hairy layer of the κ-casein’s protruding chain

is partially responsible for the micelle’s stability

through a major contribution to the negative

charge of the micelles

•

Casein micelle

• Calcium phosphate and hydrophobic interactions between sub-micelles are responsible for the integrity of the casein micelles.

• Adding an excess of Ca and phosphate results in aggregation of sub-micelles into larger units – micelles.

• The reason for this aggregation is presumably the

deposition of Ca-phosphate in the sub-micelles, which lowers their electric charge and makes them more compact.

Precipitation by casein

• One characteristic property of casein is its ability

to precipitate at pH 4.6

• Due to the complex nature of the casein

molecules, and that of the micelles formed from

them, precipitation can be caused by many

different agents.

Caseins : phosphoproteinsCaseins : phosphoproteins

• -casein

• s1-casein

s2-casein

-casein

P P P P PI I I I I

-Glu-Ser-Leu-Ser-Ser-Ser-Glu- ... -Gln-Ser-Glu-15 17 18 19 35

P P P P P P PI I I I I I I

-Gly-Ser-Glu-Ser-Thr- ... -Glu-Ser- Ile -Ser-Ser-Ser-Glu- ... -Asn-Ser-Ala-46 48 64 66 67 68 114

P P P P P P PI I I I I I I

-Val-Ser-Ser-Ser-Glu-Glu- ... -Gly-Ser-Ser-Ser-Glu-Glu-Ser-Ala-8 9 10 56 57 58 61

P P P PI I I I

- Ile -Ser-Gln-Glu- ... -Leu-Ser-Thr-Ser- ... -Glu-Ser-Thr16 129 131 143

PI

Glu-Ala-Ser-Pro-Glu-149

s1 casein

(variant B 8P)

s2 casein

(variant A 11P)

casein

(variant A2 5P)

casein

(variant B 1P)

Mol weights (Da)

23 614 25 230 23 983 19 023

Concentration (g/l)

10 2.6 9.3 3.3

Amino-acids 199 207 209 169 Phosphoserine 8 11 5 1 Carbohydrate 0 0 0 0-5 Charge at pH

6.6 - 21 - 15 - 12 - 3

Precipitation CaCl2

+ + + -

Biochemical properties of casein molecules Biochemical properties of casein molecules

Biochemistry and Biochemistry and physical-chemistry physical-chemistry of major whey of major whey proteinsproteins

Whey utilization

Fractionation of milk protein

1970 Today

-lactoglobulin

-lactalbumin Serum albumine bovine

Concentration in cow milk

2 to 4 g/l

1 to 1.5 g/l

0.1 to 0.4 g/l

Number of amino acids

Molecular weight (Da)

pHi

Position of sulfhydryl group

Number of SS bridges

168

18362

5.2-5.4

residu Cys 121

2

123

14174

4.2-4.5

no

4

582

66267

4.8-5.1

residu Cys 34

17

Main characteristics of 3 whey proteins Main characteristics of 3 whey proteins

Other whey proteins : Ig, enzymes, growth factors

Whey proteins

• Whey protein are serum proteins which are left

over in the serum after the precipitated of casein

at their isoelectric (pH:4.6) points at 20°C.

• When milk is heated, some of the whey proteins

denature and form complexes with casein,

thereby decreasing the ability of the casein to be

attacked by rennet and to bind calcium.

α-Lactalbumin

• Whey proteins in general, and α-lactalbumin in particular,

have very high nutritional values.

• α - Lactalbumin contains 123 amino acids and represents

about 25% of the serum proteins in milk

• It is present in milk from all mammals and plays a

significant part in the synthesis of lactose in the udder

• α - Lactalbumin is the most heat stable serum protein in

milk.

β-lactoglobulin• β - Lactoglobulin contains 162 amino acids.

• Major milk serum protein. about 50% of the serum protein and 8% of the protein in milk.

• There is no β -Lactoglobulin present in human milk.

• β - Lactoglobulin can be irreversibly denatured by heat.

• This stress causes rupture of intr-amolecular disulfide bonds and precipitation

• Transport of hydrophobic molecules : vitamin A, vitamin D, fatty acids (C14; C16; C18, C18:1)

• If milk is heated to over 60 °C, denaturation is initiated where the reactivity of the sulphur-amino acid of β-lactoglobulin plays a prominent part.

• Sulphur bridges start to form

1.Between the β-lactoglobulin them selve molecules,

2.Between β-lactoglobulin molecule and a κ-casein

3.Between β-lactoglobulin and α-lactalbumin. • At high temperatures, sulphurous compounds such

as hydrogen sulphide are gradually released. • These sulphurous compounds are responsible for

the “cooked” flavour of heat treated milk.

Immunoglobulins and related minor proteins

• Immunoglobulins are antibodies synthesised in response to stimulation by specific antigens.

• They are specifically present in blood. • Their content in cows’ milk is low, but some of

them are present in higher levels in colostrum and human milk.

• They can also act against “particles” such as bacteria, viruses and even fat globules, and flocculate them, a reaction called agglutination

• Serum Proteins

• Comes from blood

• Role in the transport of bile salts, fatty acids

• Mambrane proteins• Membrane proteins are a group of proteins that

form a protective layer around fat globules to stabilise the emulsion

• Some of the proteins contain lipid residues and are called lipoproteins.

Denatured proteins• As long as proteins exist in an environment with

a temperature and pH within their limits of tolerance, they retain their biological functions.

• If they are heated to temperatures above a certain maximum their structure is altered.

• The same thing happens if proteins are exposed to acids or bases, to radiation or to violent agitation.

• The proteins are denatured and lose their original solubility.

•Milk enzymes Milk enzymes

• 60 enzymes known

• Origin

Milk enzymesMilk enzymes

•

• Cells

• Leucocytes

• Bacteria

- endogenous

- exogenous ?

Lipases are enzymes that degrade fats. The major lipase in milk is lipoprotein lipase. It is associated with the casein micelle. Agitation during processing may bring the lipase into contact with the milk fat resulting in fat degradation and off-flavors. Pasteurization will inactivate the lipase in milk and increase shelf life.

ENZYMES

Proteases

The major protease in milk is plasmin.

Some proteases are inactivated by heat and some are

not. Protein degradation can be undesirable and result in

bitter off-flavors, or it may provide a desirable texture to

cheese during ripening. Proteases are important in

cheese manufacture, and a considerable amount of

information is available in the cheese literature.

Alkaline phosphatase is a heat sensitive enzyme in milk that is used as indicator of pasteurization. If milk is properly pasteurized, alkaline phosphatase is inactivated. Lactoperoxidase most heat-stable enzymes found in milk. When combined with hydrogen peroxide and thiocyanate, has antibacterial properties. It is suggested that the presence of lactoperoxidase in raw milk inhibits the disease causing microorganisms (pathogens) present in milk.

The milk fat exists as small globules or droplets dispersed in the milk serum,

Their diameters range from 0,1 to 20 µm (1 µm = 0,001 mm).

The average size is 3 – 4 µm and there are some 15 billion globules per ml.

The emulsion is stabilised by a very thin membrane only 5 – 10 nm thick (1 nm = 10–9 m ) which surrounds the globules and has complicated composition.

MILK FAT

Milks lipids 2% to greater than 50%

Source of essential fatty acids (especially linoleic

acid, &) and fat soluble vitamins (A, D, E, K)

Flavour and rheological properties of dairy products

and foods in which they are used flavour of milk fat

is superior to that of other fats. Milk fats, especially

ruminant fats, contain a very wide range of fatty

acids: more than 400

FAT GLOBULE

Milk lipids (Fat)Milk lipids (Fat)

• 3.5 - 4.5% (i.e. 35-45 g/l) for bovine milk

•Simple and complex mixture

Neutral Lipids 98.4 %

Polar Lipids1.1 %

Sterols0.5 %

MILK FAT

Milk fat consists ofo triglycerides (the dominating components), o di- and monoglycerides, o fatty acids, o sterols, o carotenoids (giving the yellow colour of

the fat)

• and vitamins (A, D, E, and K)

Principle fatty acids in milk

Milk : composition of neutral lipidsMilk : composition of neutral lipids

Neutral Lipids g/100 g lipids

Triacylglycerols 97.34

Diacylglycerols (1,2) 2.28

Monoacylglycerols (2) 0.08

Free fatty acids 0.28

Oleic acid (21.2%) C18:1 CH3-(CH2)7-CH=CH-(CH2)7-COOH

fatty acids

2/3 saturated

1/3 insaturated

Triacylglycerol

H-C-OOC-R1

H-C-OOC-R2

H-C-OOC-R3

H

H

Stearic acid (9.3%) C18:0 CH3-(CH2)16-COOH Myristic acid (14.5%) C14:0

Palmitic acid (27,5%) C16:0 CH3-(CH2)14-COOH

Fatty acids

• Most abundant fatty acids in milk are

myristic,

Saturated Fatty acids palmitic,

stearic

Unsaturated fatty acidsoleic acids.• fatty acids affects the hardness of the fat. • Fat with a high content of high-melting fatty

acids, such as palmitic acid, will be hard;• but on the other hand, fat with a high content of

low-melting oleic acid makes soft butter.

Iodine Value

Iodine value states the percentage of iodine that the fat can bind.

Iodine is taken up by the double bonds of the unsaturated fatty acids.

Since oleic acid is by far the most abundant of the unsaturated fatty acids, which are liquid at room temperature, the iodine value is largely a measure of the oleic-acid content and thereby of the softness of the fat.

Iodine value of butterfat normally varies between 24 and 46.

Conjugated Linoleic acid (CLA)

Cancer

CLA in your diet could reduce tumors

Breast Colorectal

Lung Skin

Stomach Cardiovascular disease

High blood pressure

High Cholesterol and triglycerides

Osteoporosis

Dodhi

FarmersSub Center

Main center

Factory

VMC

Milk CollectionMilk Collection

VMCSub CSub C

Main C

Collecte centerCollecte center

Problems related to milk collectionProblems related to milk collection Highly fluctuation in milk price Seasonal variation Lack of direct approach to farmers Social attachment of Dodhi with farmers

o Advanceso Emergency o High price

Lack of roads Lack of infrastructure Preservation of milk Adulteration

o Vegetable oilso Fresh or Pasteurized creamo Glucoseo Sugaro Ureao Starcho Detergento Weigh Powdero Salto Fermented Milk