Fish Microbiology and Quality Assurance

Unit 8 - Spoilage of fresh and processed fish and fishery products

8.1.1. Factors affecting spoilage
The kind and rate of spoilage of fish is affected by several factors.

1. Kind of fish
Fishes differ considerably in perishability. Some flat fishes spoil more readily than round fish because they pass through rigor mortis more rapidly. Certain fatty fishes (oil sardine) deteriorate rapidly because of oxidation of unsaturated fat/oil. Fishes high in trimethyl amine oxide (TMAO) spoil quickly and produce stale fishy smell by producing TMA.

2. Conditions of the fish when caught
Fishes that are exhausted due to struggle while capture (Ex: gill netting, long lining), lack of oxygen and excessive handling spoil rapidly. This is because of exhaustion of glycogen during struggling and causing smaller drop in pH. Feedy fish (fishes with full of food in stomach) are more easily perishable than those with empty intestine.

3. Kind and extent of contamination of fish
Contamination of fish with bacteria from various sources (mud, water, handlers, contact surfaces, slime etc.) increase bacterial load. Bacterial from slime, gill and intestine invade the flesh and cause spoilage. In general, greater the load of bacteria of fish the more rapid the spoilage. In ungutted fish (whole fish) decay of food in the gut may release odorous substances enabling diffusion of decomposition products into the flesh. Gutting the fish on boat spreads intestinal and surface slime bacteria to flesh. But, thorough cleaning will remove most bacteria, and adequate chilling will inhibit bacterial growth. Any damage to fish skin or mucous membrane will reduce the keeping quality of the product.

4. Temperature
Warmer the temperature faster will be the bacterial growth and quicker will be the spoilage. Reducing the temperature of fish by chilling will delay bacterial growth, hence, spoilage slows. Cooling temperature around zero degree celecius (0^oC), helps to delay spoilage.

5. Use of preservatives
Use of preservatives including antibiotics will prevent bacterial build up thus extend shelf life of fish.