Anaerobic Fish Spoilage by Bacteria I. Biochemical Changes in Herring Extracts

Water extracts of herring fillets were used as laboratory model substrates for the study of anaerobic bacterial spoilage of fish stored in bulk. The organisms studied ( Enterobacter sp., str. NTHC 151, Proteus sp., str. NTHC 153, and Aeromonas sp., str. NTHC 154) were selected for by an enrichment method designed to isolate the bacteria having the highest anaerobic growth yields in these herring extracts. The extracts were then inoculated with pure cultures of the bacteria and incubated anaerobically at 15°C. Chemical analyses of the extracts were carried out at the start and at the end of the incubation period. The compounds determined accounted for 88% of total carbon and 93% of total nitrogen of the sterile extracts. Ribose (free and bound), free hexoses and lactate were the main substrates for the growth of the bacteria. These compounds were converted to acetate and CO₂; hydrogen liberated by these processes was used for the quantitative reduction of trimethylamine oxide to trimethylamine. Fermentation balances support the contention that the biochemical changes observed represent the quantitative dominating chemical events in the herring extracts as a result of the development of the spoilage bacteria.