MARKET MILK

Module 6. Common dairy operations

Lesson 25
HOMOGENIZATION - EFFECT ON MILK PROPERTIES

25.1 Introduction

Homogenization prevents phase separation of fat into cream layer during storage and enhances the richness of mouth feel as well as due to an increased surface area. It involves physical changes in milk protein, resulting in lower curd tension and possibly increased digestibility due to faster coagulation in the stomach.

25.2 Effect of Homogenization on Physico-Chemical Properties of Milk

25.2.1 Reduction of fat globules size

Reduction of fat globule size to < 2 µ prevents formation of cream layer and increases the surface area of the fat above 6 times.

25.2.2 Whiter milk

Homogenization of milk increases its whitening power due to an increase in the number and surface area of the fat globules. Adsorption of casein miscelles and serum proteins on newly created fat globules surface increases scattering of light thereby causing whiter appearance.

25.2.3 Physiology of nutrition

Homogenization has been reported to improve the digestibility of milk due to increase in the number and surface area of the fat globules.

25.2.4 Flavour of milk

Homogenized milk has a uniform flavour throughout. It tastes richer, smoother and creamier than unhomogenized milk due to an increase in the surface area of the fat globules which are uniformly distributed in milk.

25.2.5 Sensitivity to lipase

Homogenized milk is more susceptible to enzymic activities, especially lipase action, than unhomogenized milk. Lipase can cause rancidity rapidly in homogenized raw milk.

25.2.6 Susceptibility to oxidation

Homogenized milk is more susceptible to oxidized flavours caused by natural or artificial light than un¬homogenized milk. To prevent development of off-flavours, homogenized milk must be packaged in opaque containers, such as cartons, plastic containers or coloured bottles.

25.2.7 Sediment on storage

Homogenized milk may develop dark sediment at the bottom of the container after standing for 24 h. This is due to settling of cells, foreign matter and casein particles. In unhomogenized milk, these particles are usually held by the fat globules. To prevent the sediment formation, homogenized milk must be filtered or clarified, preferably before homogenization.

25.2.8 Bacterial count

There will be an apparent increase in bacterial count after homogenization due to the break-up of clumps and colonies of organisms.