Investigation into toxins and pathogens implicated in fish meal production
The major toxins and pathogens in fish meal were investigated because of food industry, public and animal health concerns. The effect of processing, the type of raw material used and storage conditions on the main toxin, histamine which causes gizzard erosion in poultry, and its formation in fish meal were investigated. The results showed that histamine and histamine-like amines in fish meal varied in levels between batches depending on the quality of raw material and type of fish used. The relationship between histamine and histamine-like amines levels was unclear. During laboratory processing of fish meal it was found that most histamine concentrated in the stickwater which had implications for the use of stickwater meal in feeds. Interestingly, histamine was detected in the stickwater meal of cod as well as mackerel. A decrease in histamine in mackerel meal and cod meal during processing was observed with respect to levels in raw material. The decrease maybe originated after the cooking stage especially in the stickwater meal (probably due to bacterial recontamination or enzymatic reactions). The decrease could be due to histamine either adhering to the equipment used or breakdown to its metabolites or derivitising to gizzerosine. Since very low levels of histamine were observed from meals produced from reasonably fresh fish, the control of histamine therefore is best achieved at the raw material stage of production. During storage trials, there was no increase in histamine levels but a decrease occurred gradually with time at 15°C, 70% RH. Rapid loss occurred at 25 and 30°C, 80% RH and heavy mould growth was also observed, although no mycotoxins were detected in analysed samples. Routine analytical methods were studied and compared for the requirements of the fish meal industry and poultry farmers. Problems occurred with the colorimetric method when applied to fish meal and fish samples containing bones due to the presence of calcium. It was modified for routine histamine analysis. Thin Layer Chromatography was the second alternative. Although High Performance Liquid Chromatography was suitable for analysing histamine and histamine-like amines together, it did lack in meeting industrial requirements. Since the modified colorirnetric method was labour intensive, despite its other advantages, there was still a need for a simpler and quicker method of analysis. For this reason, research work was carried out to develop an immunoassay for histamine analysis. The results showed that it was possible to raise antibody against histamine and suggested future research potential. Hygienic conditions of laboratory scale fish meal production were investigated. The presence of Salmonella, which leads to human salmonellosis, and E. coli 0157:H7 which also cause human food poisoning were studied. The results showed that the critical control point of fish meal production was after cooking, since recontamination can occur. Salmonella was present in several batches of commercial and laboratory processed samples, but no E. coli 0157:H7 was detected in analysed samples. Three rapid methods were compared to traditional method for Salmonella analysis particularly in fish meal. The immunoassay method introduced by Institute of Food Research, Norwich was found the most suitable because it was sensitive, specific and took about one day to complete.