Processing of Milk - Contd...

Addition of Lysozyme

The enzyme lysozyme is present in the form of muramidase in milk and egg white and many commercial preparations are available for its use in cheese milk to control clostridia and butyric acid fermentation. The required dosage of lysozyme is 1 – 2 g per 100 litres of milk. The extraneous addition of the enzyme lysozyme is obviated due to the development of genetically modified lactic acid bacteria, which are capable of producing lysozyme.

Microfiltration / Bactocatch

This is a recent development, which uses microfiltration technique to filter the bacteria. The disadvantage in the use of sodium nitrate and lysozyme due to their restriction in use in milk in many countries is obviated in this method. Here the skim milk is prewarmed to 45°C and then microfiltered and concentrated to 10 to 20 fold. The porosity of the membrane is large enough to allow all the milk solids but small enough to retain the bacteria and their spores.

The retentate, which is approximately 5% of the original volume of milk, is added with desired volume of cream in order to obtain the required fat percentage in the cheese milk and heated to 110 – 130°C in a plate heat exchanger and this process is known as High Temperature Treatment (HTT). Then the HTT standardized retentate – cream mixture is cooled and blended with micro filtered permeate, pasteurized at 72°C for 15 seconds and cooled to 30°C and then finally transferred to cheese vat. The advantage claimed for this method includes development of off flavours and coagulation of milk proteins are avoided. Further more most of the spore formers are destroyed during sterilization.