Fish Microbiology and Quality Assurance

Unit 4 - Food preservation techniques and microorganisms

4.1.1 Preservation of foods with low temperature
Low temperature preservation of food is based on the principle of reducing the microbial activity by subjecting to low temperature condition. As all metabolic activities of microorganisms are catalyzed by enzymes, and enzyme reactions are dependent on temperature, the low temperature slows down enzyme activity, thereby brings about reduction in microbial activity. The reduced microbial activity prolongs shelf life of foods.

Shelflife of temperate and tropical water fish
Activity of microorganisms is known to decrease by two fold with every 10^oC decrease in temperature. Fresh fish from temperate waters generally have prolonged shelflife than tropical fishes. This is because of the low ambient temperature in temperate waters coupled with low body temperature of fish, being cold blooded, lowers both enzymatic and bacterial growth, thereby reduces deteriorative change and helps in extending the shelflife.
In tropical waters, the high ambient temperature and high body temperature of harvested fish promotes deteriorative changes by enzymes and microorganisms and thus hastens the spoilage.

Methods of low temperature presentation
Low temperature preservation is generally attained by employing three different temperature conditions. They are;

• Chilling temperature: keeping foods at 10-15^oC (slightly above refrigerated temperature).
• Refrigerator temperature : Keeping foods at 0~7^oC
• Freezer temperature: Storage of foods below -18^oC.

In Fisheries, fish are preserved by keeping at chilling temperature and by freezing.