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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
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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
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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
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Species
Breed
Stage of lactation
Season
Sanitary state
Feed
Milk : variable compositionMilk : variable composition
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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
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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
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Casein micelle : Casein micelle : Molecules of caseins Molecules of caseins ++ Minerals (calcium phosphate)Minerals (calcium phosphate)
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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
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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
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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
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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,
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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
•
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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.
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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.
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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
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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
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Biochemistry and Biochemistry and physical-chemistry physical-chemistry of major whey of major whey proteinsproteins
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Whey utilization
Fractionation of milk protein
1970 Today
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-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
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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.
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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.
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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)
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• 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.
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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
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• 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.
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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.
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•Milk enzymes Milk enzymes
• 60 enzymes known
• Origin
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Milk enzymesMilk enzymes
•
• Cells
• Leucocytes
• Bacteria
- endogenous
- exogenous ?
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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
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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.
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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.
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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
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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
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FAT GLOBULE
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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 %
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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)
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Principle fatty acids in milk
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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
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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.
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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.
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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
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Dodhi
FarmersSub Center
Main center
Factory
VMC
Milk CollectionMilk Collection
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VMCSub CSub C
Main C
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Collecte centerCollecte center
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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