Storage and keeping quality of fermented milks

During the storage of fermented milks, various changes may occur such as microbial,enzymatic and abiotic spoilage. The spoilage of yoghurt is discussed hereunder:

i. Microbiological Spoilage

Microbial spoilage refers to an alteration of the outer appearance of yoghurt caused by micro-organisms. The culture of yoghurt does not cause this type of spoilage. On the other hand, contaminants capable to grow at lower temperatures and at a low pH, form colonies or film on the surface of yoghurt deteriorating its appearance. The microbial spoilage of yoghurt is presented in table . 

The microbial spoilage of yoghurt

ii. Enzymatic Spoilage

Enzymatic spoilage (Table ) is attributed to the activity of enzymes present in yoghurt. These enzymes derive from both the yoghurt culture and contaminants.Other enzymes such as milk enzymes or those originating from the microflora of raw milk, which eventual resist heat treatment of the milk have no practical significance.

Table  shows that contaminants are the main causative agents for the enzymatic spoilage of yoghurt. They adversely affect the taste and consistency of the final product.

The Enzymatic spoilage of yoghurt

iii. Abiotic (Chemical) Spoilage

The spoilage occurs without the activity of microorganisms and enzymes. Table  shows the abiotic spoilage of yoghurt (changes in protein, fat, lactose, vitamins,mineral salts and in additions such as fruit base or other flavorings) influenced by the gaseous oxygen and light.

The Abiotic spoilage of yoghurt