Properties and Composition of Milk

Dr. Aarab lundDvm, rvmp

Milk Def: It’s the lacteal secretion, that obtained by the complete milking of one or more healthy cows and must have following characteristic;practically free from colostrumcontains not less that 8 ¼% of milk-solids-not-fat Contain not less than 3 ¼% of milk fat.OrMammary Gland’s secretion 3-4 days after Parturition.

milk - fat (skim milk) Plasma

plasma - casein micelles (whey) Serum

Total Solid-Fat. E.g.Proteins, lactose, minerals, acids, enzymes, vitamins.

solids-not-fat (SNF):

Total Milk Solids fat + SNF

Terms

Water 87% Fat 3.5-3.7%

Lactose 4.9% Proteins 3.5%

GROSS COMPOSITION OF MILKAverage gross composition of Cow’s Milk

Breeds Diet

Season Stage of lactation

CHANGES IN MILK COMPOSITION

Only Food for Neonates Furnish all Nutrients

Immunological Protection Best Natural Sources of Calcium

Importance of Milk

Emulsion

A fine dispersion of minute droplets of one liquid in another in which it is not soluble..

Butter is an emulsion of water in fat.Milk is an emulsion of fat in water

Other e.g. margarine, mayonaise, cream, and salad dressing.

Basic Properties of Milk

Physical Properties of Milk1- Color:Buffalo(White color) Fat globules in emulsion form.Protein in colloidal form.

Cow(Yellowish (creamy) color) Presence of Carotene and Xanthophyll pigments.

2- Reaction:Fresh milk is amphoteric in reaction as it contains acid and base.Milk is an excellent buffer as it contain:

Protein.Phosphate.Bicarbonate.Citrate.

** PH of fresh milk:6.6 – 6.8 Cow's milk but change due to;Mastitis Late period of lactation.

3- Specific Gravity: It is the ratio between weight of a given volume of milk compared with the same volume of water at a specific temperature. It measure total solids of milk, and determine if any constituent added or removed from milk.. Measured by Lactometer. Normal specific gravity:

1020 – 1030 Cow's milk.

4- Taste: Normal characteristic milky taste. Milk taste changed in case of :

Souring: due to increased acidity. Boiling: due to certain biochemical changes and evaporation of volatile fatty acids. Late stage of lactation: due to increase chloride percent. Mastitis: inflammation of udder.

Physical Properties of Milk

5- Freezing point of milk:It is the temperature at which the liquid milk freeze or crystallize.The freezing point of cow or buffalo milk ranges from (-0.53) to (-0.57) °C with average (-0.55) °CMilk freezes at a temperature slightly lower than that of water due to the soluble constituents in

milk such as lactose, minerals which lower the freezing point.

6- Boiling Point:Milk boiling point is 100.5 °C , more than water due to presence of dissolving substances

8- Cream Line Formation:When milk left at room temperature the fat globules coalesce, clumped at surface of the container and form

cream line.

Physical Properties of Milk

Milk Fat Globule

Fat Globule Membrane(FGM)

Density

Milk Fat

Milk fat/Lipid/Fat Globule

Exists as large globules varying in size from 0.1-10um in diameter.

Most variable component of milk. Mostly (98-99% triglycerides). Triglycerides/ triacylglycerol = glycerol + 3 fatty acids

Milk Fat Globule Continue

Smoothness and palatability to fat containing products. Remaining 1- 2% of milkfat is composed of Pospholipid, Sterols,

Carotenoids, Fat soluble vitamens A, D, E & K and some traces of Free Fatty Acids.

Milkfat contains high proportion of short chain fatty acids (C4-C10)

Butyric acid (C4) is unique to milkfat.

Fat Globule Membrane(FGM)

Encapsulated by a lipid bilayer membrane made up of proteins, phospholipids, lipoproteins, cerebrosides, nucleic acids, enzymes, trace elements, and bound water.

Provides stabilization for the fat globule in the aqueous environment of the milk serum.

Ruptured, the fat globules join together into a solid mass of fat. (This is what happens during the production of butter).

Density of Fat Globule

Degree of compactness of Fat Globule in Milk. Largest particles in milk but they are also the lightest. Lower density than milk serum, so the globules rise to the

surface, which is how cream is formed. The density difference is used to separate milk fat from whole

milk in high speed, continuous flow, centrifugal separators.

Deterioration of Milk Fat

Enzyme-> Lipase Light Oxygen

Milk Fat

Lipolysis

Native milk Airborne bacterial contamination Bacteria for fermentation Somatic Cells

Rancid Flavor

Pasteurization

Degradation

Off- Flavor

Oxida

tion

Off- Flavor i.e. Penty,Fishy,Metalic

Fat Like SubstanceMilk also contain small amounts of:Phospholipids:Milk phospholipids are lecithin, cephalin, sphingomyelin.Cholestrol: It is insoluble in water, sparingly soluble in cold alcohol or petroleum ether, and soluble in hot alcohol and most other organic solvent. Its solubility in cold ethyl acetate differentiates it from many other lipids. Fat soluble vitamins: Milk contain at soluble vitamins A, D, E & K.Carotenoids: Milk contain following Carotenoids; alpha carotene, Beta carotene, Gamma carotene, lycopene etc. Free fatty acid: Milk also contain free fatty acids in small proportion.