The distribution of Morganella morganii in fish and fish products on the market was investigated. Sliced raw fish both wrapped and unwrapped were frequently contaminated with Morganella morganii.
We then investigated the effect of the temperature on the formation of histamine in raw fish and fish products inoculated or not inoculated with Morganella morganii, paying special attention to the effect of cold storage. During the storage at 5°C or 7.5°C, histamine was hardly produced in sliced raw tuna not inoculated with Morgalla morganii and the sliced raw yellowtail inoculated with Morganella morganii, but during the storage at 10°C, much histamine was produced in both fish.
When 10 g of jack mackerel (for frying) inoculated with 1 ml of a suspension of Morganella morganii at 2 × 10⁶/ml was inoculated for 6 hr at 30°C, the formation of histamine comtinued even during the storage at 5°C. In jack mackerel (for frying) inoculated with Morganella morganii, the amount of histamine formed depended on the viable count of Morganella morganii. During the storage at 5°C, the growth of Morganella morganii was suppressed but when the viable count reached around 10⁸/g, histamine was produced.
The effects of the concentration of sodium chloride on histamine formation was investigated. Histamine was hardly produced in the meat with 7.5% or 25% sodium chloride but was produced much in the meat with 2% and 5% sodium chloride.