Why Seafood Spoils
Spoilage begins as soon as seafood species die. Their normal defense mechanisms stop working and a series of changes begin that cause spoilage. These changes are caused by bacteria, enzymes and chemical action.
Spoilage By Bacteria
Bacteria are the most important cause of seafood spoilage. Millions of bacteria are present in the surface slime, on the gills, and in the gut of living seafood species. When seafood species die, bacteria, or the enzymes they produce, invade the flesh through the gills, along blood vessels, and directly through the skin and belly cavity lining. In the flesh, bacteria grow and multiply, producing compounds which are responsible for "fishy" odors and flavors, and discolorations associated with stale seafood. If food poisoning bacteria are present, they can multiply and cause illness when the seafood is eaten.
Spoilage By Enzymes
Many different enzymes are present in living seafood species. They help build tissue, contract and relax muscles, and digest food. When seafood species die, enzymes continue to work and start to digest or breakdown the flesh. This causes the flesh to soften and lowers the quality. Enzymes also produce more food for bacteria to feed on, increasing the rate of spoilage.
Spoilage By Chemical Action
Oxygen in the air can attack unsaturated oils in seafood causing rancidity, off-odors and off- flavors. This is especially important in fatty fish such as salmon and mackerel.
Slowing Seafood Spoilage
All of the changes that cause seafood spoilage are affected by temperature. High tempera tures speed spoilage and low temperatures slow spoilage. For many seafood species, increasing the temperature from 32F to 40F doubles the rate of spoilage and cuts the shelf life in half.Sanitation is also important. Contamination of seafood by bacteria from dirty ice, containers and surfaces can increase the number of bacteria on seafood and speed spoilage. Contamination with food poisoning bacteria can cause illness when the seafood is eaten. Keeping seafood handling and storage equipment clean reduces bacterial contamination and slows spoilage.
Shelf Life
The approximate shelf life for fresh fish fillets is:
| Holding Temperature (°F) | High Quality
Shelf Life | Edible Shell Life |
|---|---|---|
| 90 | 14 hours | 1 day |
| 60 | 1½ days | 2½ days |
| 42 | 3 days | 6 days |
| 32 | 8 days | 14 days |
| 30 | 10 days | 17 days |
| 29 | 12 days | 20 days |
Effect of Temperature on Shelf Life
| Holding Temperature (°F) | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 29 | 30 | 32 | 34 | 36 | 38 | 40 | 45 | 50 | 55 | 60 | 65 | |
| Time at Holding Temperature | Equivalent Age of Product in Days at 32°F | |||||||||||
| 2 hours | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.2 | 0.2 | 0.3 | 0.4 | 0.5 | 0.7 |
| 4 hours | 0.1 | 0.1 | 0.2 | 0.2 | 0.2 | 0.3 | 0.3 | 0.5 | 0.7 | 0.9 | 1.1 | 1.3 |
| 6 hours | 0.2 | 0.2 | 0.3 | 0.3 | 0.4 | 0.4 | 0.5 | 0.7 | 1.0 | 1.3 | 1.6 | 2.0 |
| 12 hours | 0.3 | 0.4 | 0.5 | 0.6 | 0.7 | 0.9 | 1.0 | 1.5 | 2.0 | 2.6 | 3.3 | 4.0 |
| 18 hours | 0.5 | 0.6 | 0.8 | 0.9 | 1.1 | 1.3 | 1.6 | 2.2 | 3.0 | 3.9 | 4.9 | 6.0 |
| 1 day | 0.7 | 0.8 | 1.0 | 1.2 | 1.5 | 1.8 | 2.1 | 3.0 | 4.0 | 5.2 | 6.5 | 8.0 |
| 2 days | 1.4 | 1.6 | 2.0 | 2.5 | 3.0 | 3.6 | 4.2 | 5.9 | ||||
| 3 days | 2.1 | 2.4 | 3.0 | 3.7 | 4.5 | 5.3 | 6.3 | |||||
| 4 days | 2.8 | 3.2 | 4.0 | 4.9 | 7.1 | 8.4 | ||||||
| 5 days | 3.5 | 4.0 | 5.0 | 6.2 | ||||||||
| 6 days | 4.1 | 4.7 | 6.0 | |||||||||
| 7 days | 4.8 | 5.5 | 7.0 | |||||||||
| 8 days | 5.5 | 6.3 | 8.0 | |||||||||
| 9 days | 6.2 | 7.1 | ||||||||||
| 10 days | 6.9 | 7.9 | ||||||||||
| 11 days | 7.6 | |||||||||||
| 12 days | 8.3 | |||||||||||
| Example | |||
|---|---|---|---|
| Actual Elapsed Time | Temp. | Equivalent Age at 32°F | |
| Fish Caught | 2 hours | 60°F | 0.5 days |
| Storage on vessel | 3 days | 34°F | 3.7 days |
| Processing | 12 hours | 45°F | 1.5 days |
| Distribution | 12 hours | 36°F | 0.7 days |
| Retail case | 1 day | 38°F | 1.8 days |
| TOTAL | 5.1 days | 8.2 days | |
| Remaining high quality shelf life at | 32°F | 5 hours | |
| Remaining edible shelf life at | 32°F | 5.8 days | |
| 40°F | 2.7 days | ||
References:
Doyle, J.P. 1989. Seafood shelf life as a function of temperature. Alaska Sea-Gram No. 30. Marine Advisory Program, University of Alaska, Fairbanks.Ronsivalli, L.J. 1982. A recommended procedure for assuring the quality of fish fillets at point of consumption. Mar. Fish. Rev. 44:8.
Strasdine, G. 1983. A guide to estimating shelf life of fresh groundfish fillets. Industry Information Report No. 9, B.C. Research, Vancouver, B.C.
The author is Robert J. Price, Seafood Technology Specialist, Department of Food Science & Technology, University of California, Davis, California 95616
UCSGEP 89-3, August 1989
This work is sponsored in part by NOAA, National Sea Grant College Program, Department of Commerce, under grant number NA85AA-D-SG140, project number A/EA-1, through the California Sea Grant College Program, and in part by the California State Resources Agency. The U.S. Government is authorized to reproduce and distribute reprints for governmental purposes.
University of California, the United States Department of Agriculture, and the United States Department of Commerce cooperating.
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