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Milk: Physico-Chemical Properties
Booklet No. 277
Dairy Management & Milk Products: DMMPS - 7
Contents
Preface
I. Introduction
II. Physical Properties
1. Taste and odour
2. Colour
3. Specific gravity
4. Boiling point
5. Freezing point
6. Refractive index
7. Electrical conductivity
8. Specific gravity
9. Co-efficient of thermal expansion
10. Thermal conductivity
11. Viscosity
12. Surface tension
13. Germicidal properly
III. Chemical Properties
1. Acidity
2. PH
3. Buffering action
4. Oxidation -reduction potential
IV. Conclusion

Preface

Milk cooperatives are mushrooming in our country as a socio-economic development programme organized both by NGOs and government agencies. However, people are seldom aware that milk is a bio-chemical substance and hence its handling require basic knowledge of its physical and chemicals properties which are briefly explained in this booklet.

Dr. K.T. Chandy, Agricultural & Environmental Education

I. Introduction

Milk is the most common balanced food prepared by nature for a newly born animal. However by employing modern techniques the production potential of a milch animal is increased beyond the requirement of its young one so that human also benefit from the nature's gift of balanced food. Commercialization of milk and milk products necessitates the bulk handling of milk in diary plants big or small, at the rural areas or urban areas by illiterate, semi-literate or illiterate people. However, methods of such handling such as collecting, storing, pasteurizing, packing, transporting etc. are to a great extend determined by the physical and chemical properties of the milk. The most common properties among them are explained for the benefit of the common people.

II. Physical Properties

The physical properties of milk are freezing point, colour, specific gravity, boiling point, refractive index, electrical conductivity, co-efficient of thermal expansion, thermal conductivity, velocity, surface tension and germicidal property. These arc briefly described as follows.

1. Taste and odour
To most of the people normal milk tastes slightly sweet and his mild aromatic flavour and aroma. The sweet taste comes from the flavour and aroma principally from milk sugar and butter fat. When milk is produced under uncleaned surroundings or from animals which are in their late lactation, the taste and aroma of milk is adversely affected. Feeding of certain weeds or fodder and infection of udder also causes abnormal flavour and taste in milk.

2. Colour
Milk contains several pigments which impart colour to it. Cows milk is always slightly yellow in colour due to the presence of carotene. The intensity of yellow colour in cows milk increase when they are fed with more green fodder. Buffalo milk is white due to absence of carotene. White opaque colour of milk seen in reflected light is caused by the interference with the passage of light caused by the fat and the colloidally dispersed substances. When milk fat is removed from the milk then skim milk shows greenish tint which is due to the presence of riboflavin or lactochrome. Riboflavin have a tendency to convert all carotene into vitamin A which is a colourless substance.

3. Specific gravity
The term specific gravity (SG), as applied to milk means the weight of given volume of milk compared with the weight of the same volume of water at the same temperature. Generally 15.6o is the temperature at which SG of milk is determined. Lactometcr is used to determine the SG of milk. The standard lactometers arc calibrated to read correct when the temperature of milk is 15o Centigrade. The most common lactometer used for finding out the SG of milk are zeal and Quevenne make. The SG of milk can also be determined by...
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