Studies on histamine-decomposing bacteria in marine food products

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Histamine (Hm) is known as the causative compound of scombroid fish poisoning. The accumulation of Hm during the storage of fish meat does not depend only on Hm-producing bacteria but also on Hm-decomposing bacteria. Most studies concerning Hm problems of sea products, however, have focussed on the type of Hm-producing bacteria and their avility to produce Hm, while the decomposition of Hm has hardly been studied. In order to clarify the mechanisms of Hm accumulation, the distribution and roles of Hm-decomposing bacteria during the storage of fish meat, and in kusaya gravy, fish sauce and shiokara were studied. The results are as follows ;Changes in the numbers of both Hm-producing and Hm-decomposing bacetria and Hm contents were examined during the storage of common mackerel at 5 and 30ﾟC for two months each throughout a year. In the case of samples stored at 5ﾟC,the Hm contents, once accumulated, decreased and disappeared when the sample putrefied as Hm-decomposing bacteria took over … More (more than 10^6/g) and the pH value became neutral. At 30ﾟC storage, the Hm content did not always decrease, suggesting the Hm-decomposing ability of the bacteria might therefore be inhibited at 30ﾟC.Pseudomonas putida seemed to play a major role in the decomposition of Hm accumulated during the storage of the fish meat.It was found that changes in polyamine contents in the samples did not always follow the same general pattern and did not correlate with the progress of decomposition. So polyamines would not be a reliable indicator of fish decomposition.Kusaya gravy had none or less than 10^1/ml histamine-producing bacteria and 10^4-10^6/ml of Hm-decomposing bacteria. The pH values of kusaya gravy were in the optimal range for bacterial Hm decomposition. It is therefore assumed that Hm hardly accumulates in kusaya gravy.Hm contents of fish sauce were 30-71mg/100ml. Hm-producing bacteria counted on 20%-NaCl medium was 8*10^2/ml, suggesting the possible production of Hm in fish sauce containing extremely high salt concentration.During the fermentation process of shiokara, neither Hm-producing nor Hm-decomposing bacteria were detected. It was suggested that Hm accumulation hardly occurs in shiokara. Less