Physico chemical properties of milk

1. PHYSICO-CHEMICAL PROPERTIES OF MILK
Dr. Ashish Saini
Department of LPT,
PGIVER (RAJUVAS), Jaipur

2. PHYSICO-CHEMICAL PROPERTIES OF
MILK CONSTITUENTS
1. Water
 Dispersion medium in which rest of the components are
dissolved
 Mostly free in form
2. Milk fat/lipids
 2-5 µ in size
 oil in water emulsion
 Fat globules are coated with fat globule membrane (FGM)
 FGM is made up of phospholipids and proteins in the form of a
complex and stabilize the fat emulsion

3.  Chemically, milk fats are glycerides of fatty acids
 On hydrolysis→ fatty acid + glycerol
 Milk fatty acids Saturated f.a. 65%
Unsaturated f.a 32% MUFA
3% PUFA
3. Milk Proteins casein and whey proteins
 Precipitated by acid, rennet, heat, alcohol and concentration
(a) Casein
 80-82% of total milk proteins
 Exists as Calcium-caseinate complex
 Colloidal state

4.  Three types of caseins are found in milk- α casein, β-
casein, γ-casein
 α casein – plays role in stabilization of micelles in
milk
αs casein – Calcium sensitive casein
K-casein – Calcium insensitive casein & site for rennin action
(b) Whey
 18-20% of the milk proteins
 Also known as milk serum/plasma
 2 types namely, α-lactalbumin and β-lactglobulin
 α-lactalbumin and β-lactglobulin are easily coagulated by heat
 β-lactglobulin acts as carrier of vitamin A

5. 4. LACTOSE/ MILK SUGAR
 Exist only on milk
 Responsible for defect “sandiness” in ice cream and
sweetened condensed milk.
 Fermented by bacteria and produce Lactic acid and organic
acid.
 Useful in production of cultured milk products
 Responsible for spoilage of milk and milk products by
souring.

6.  Minerals : K, Na, Mg, Ca, P, citrate, Cl, sulphate and bicarbonate.
 Minor milk constituents
(a) Phospholipids
 Act as emulsifying agents
 lecithin, cephalin and sphingomylin
 Lecithin important constituent of fat globule membrane and contributes
to “richness” of flavour of milk and milk products
 Oxidative changes in Phospholipids give rise to metallic/oxidized
flavour in milk

7. (b) Pigments
 2 types- fat soluble (carotene and xanthophyll) and water
soluble (riboflavin)
 Carotene is reddish brown in colour and imparts yellowish tinge
to milk, cream, butter, ghee etc. Carotene acts as precursor of
Vitamin A and also as an antioxidant.
 1 mole of carotene = 2 moles of Vitamin A.
 Cows able to transfer more carotene from feed to the milk in
comparison to buffaloes
 The carotenoid content of buffalo milk = 0.25-0.48µg/g while that
of cow milk = 30µg/g.
 Riboflavin, besides being a vitamin imparts characteristic
greenish colour to whey

8. (C) Enzymes
 Analase (diastase)- starch splitting
 Lipase- fat splitting (leads to rancid flavour)
 Phosphate – splits certain phosphoric esters (basis of
phosphatase test for pasteurization efficiency)
 Protease – protein splitting
 Peroxidase and catalse- decompose H2O2
(d) Cholesterol
 Present in true solution in the fat
 Also present in complex form with protein in the SNF portion
(e) Vitamins
 Both fat and water soluble vitamins are present in milk.

9. PHYSICO-CHEMICAL PROPERTIES OF MILK
Acidity of milk - Freshly drawn milk amphoteric in nature.
 ‘Natural’ or ‘apparent’ acidity of milk determined by titration
(Titratable acidity/T.A.),
 Casein, acid-phosphates, citrates etc. responsible for natural acidity.
 Acidity of milk is directly proportional to SNF content.
 The T.A. of cow milk is 0.13-0.14% and buffalo milk is 0.14-0.15%
and it expressed as % of lactic acid.
 ‘Developed’ or ‘real’ acidity: Due to bacterial action leads to
production of lactic acid.

10. PH OF MILK
 pH- cow milk is 6.4-6.6 and 6.7-6.8 for buffalo milk.
 pH increases in case of mastitis and decreases in
bacterial infections.
 pH and acidity of milk depends upon-
 Species
 Breed
 Individuality
 Stage of lactation
 Health of animal

11. DENSITY AND SPECIFIC GRAVITY:
Water 1.0
Cow milk 1.028-1.030
Buffalo milk 1.030-1.032
Fat 0.93
Protein 1.346
Lactose 1.666
SNF 1.616
Salts 4.12
Skim milk 1.035-1.037

12.  Determined using lactometer
 Addition of water decreases specific gravity and vice versa
 Removal of fat (skimming) increases specific gravity
 specific gravity of milk expressed at 60 ° F or 15.6°C


13. FREEZING POINT OF MILK
Cow milk -0.547°C
Buffalo milk -0.549 °C
Addition of water ↑FP
Pasteurization No effect
Sour milk ↓ FP
Lactose, SNF ↓ FP
Boiling ↑FP
Sterlization ↑FP

14.  Measured by Horvet’s cryoscope
 The depression in freezing point of milk: detect up to
3% water addition.
Boiling point of milk
 Milk usually boils at 100.15°C. Addition of water lowers the
concentration of dissolved substances leading to the decrease
on BP. ↑ in concentration of milk leads to ↑ in BP of milk.

15. COLOUR OF MILK
Cow milk Yellowish creamy white
Buffalo milk Creamy white
Skim milk Bluish tinge
Whey Greenish yellow (Riboflavin)
Flavour
•It is a sensory property in which both odour and taste interact.
•The flavour of milk is a blend of the sweet taste of the lactose
and salty taste of minerals, both of which are damped down
by the proteins.
•The phospholipids, fatty acids and fat of milk also contribute to
the flavour.
•The sulfhydryl compounds lead to cooked flavour of milks.