Fish Microbiology and Quality Assurance

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

8.2.5. Microbiology and spoilage of cured fishery products
Salting and drying are the most common methods used for curing of fish. The preservative effect of salted and or dried fishery products is due to lowering of water activity. Bacterial counts of fully dried seafood are generally low, unless there has been extensive surface contamination. Spoilage of such products is mainly caused by halophilic bacteria which can persist on the surfaces of contaminated cured seafood. However, the microbiological hazards due to pathogenic microorganisms are negligible in cured or salted seafood products.
Smoked seafood products vary widely in microbial stability depending on the nature and degree of severity of processing. Heavily salted, hot smoked products are microbiologically similar to the fully dried products since their water content is too low to support bacterial growth and hence pose little or no hazard. Lightly smoked products that are brined only enough to improve a flavour carry a mixed microbial population and are only slightly more stable than unprocessed fish. Generally, Gram positive bacteria dominate the microflora of such products soon after preparation but Gram negative bacteria gradually become more numerous during refrigerated storage and are ultimately responsible for their spoilage. The hot smoked fishery products that have not been adequately dryed are of high risk due to selective outgrowth of C. botulinum resulting from favourable Eh and elimination of competing bacteria.