Food Science and Processing

FOOD SCIENCE AND PROCESSING 3 (2+1)

Lesson 23 : Processing and Preparation of Fish

Spoilage

Fish is a highly perishable food. The spoilage of fish is due to three causes.

1. Microbiological: While live fish is bacteriologically sterile, there are large number of bacteria on the surface slime and digestive tracts of living fish. When fish is killed, these bacteria multiply rapidly and attack all tissues. Since the bacteria live on the cold-blooded fish at rather low ocean temperatures, they are adapted to cold and continue to grow even under refrigerator conditions. Growth of micro-organisms and enzymes affect the quality.


2. Physiological: Fish struggle when caught and hence all the glycogen stores in the muscle and liver are used up. There is no glycogen left for being converted into lactic acid which helps to increase the pH of the tissues and retard the multiplication of microorganisms.


3. Biochemical: The important biochemical change leading to the development of the characteristic fishy off odour is due to the production of trimethylamine by the action of bacterial enzymes on phospholipids and choline present in fish. The fats present in fish are highly unsaturated. By the action of bacterial lipases and lipoxidases, free fatty acids are produced and the fat undergoes oxidative rancidity. This results in additional oxidised and rancid off-odours and off-flavours.