Changes in the levels of histamine during processing and storage of fish meal

Processing and storage trials were carried out under controlled laboratory conditions to investigate the effect of processing and storage conditions on histamine formation during fish meal production. It was found that most histamine concentrated in the press liquor (stickwater) meal after processing. Histamine levels were mainly decreased in mackerel samples but increased in cod samples after processing into fish meal. Histamine was detected in the fish meal samples of fish offal of both cod and mackerel. No bacterial growth was observed in the press-cake when fish was cooked and pressed during fish meal production. After drying of solids and the stickwater, bacterial growth was observed. This is an indication that fish meal is apparently microbiologically hygienic after cooking process, then recontamination occurs. That samples were packed in polyethylene bags seemed to show a slight increase in histamine levels up to fifth week but a significant decrease (P<0.001) occurred gradually for the samples stored at 0, 20, 30 and 35 °C. However, storage temperature did not have significant effect on histamine levels for the packed samples. The results of storage trial with unpacked samples showed that histamine values decreased gradually with time at 15 °C and 70% relative humidity (RH). Rapid loss and heavy mould growth occurred at 25 and 30 °C with 80% RH.