Effect of processing on histamine levels in mackerel

Histamine, which is produced by bacterial decarboxylation of histidine in pelagic fish, is implicated in scombrotoxin poisoning. This investigation was carried out to determine the effect of processing on histamine levels in the flesh of mackerel (Scomber scombrus). Two methods of determining histamine in fish samples were evaluated. A calorimetric method, involving coupling of histamine to give an azo-dye, was found to be simple and reliable and was used to determine histamine levels in a large number of canned and salted/dried fish samples. A gas chromatographic method was found to be unsuitable for use in determining histamine at levels found in fish and fish products. The stability of standard histamine solutions at different pH values was investigated by subjecting to heat (121°C for 180 min). This treatment showed a loss of less than 5%. Various compounds (glucose, ribose, ascorbic acid and benzaldehyde) that react with histamine, were added to standard histamine solutions to investigate the possibility of decreasing histamine levels in canned products. The' heat treated solutions showed a loss of histamine of less than 10% and distinct browning occurred in the solutions containing glucose and ribose. The effect of heat treatment (115°C for 90 min) on histamine in the presence of fish flesh was also examined. Variable results were obtained with a mean loss of histamine of only about 16)\,. When this experiment was repeated with the addition of glucose it gave a higher loss of about 36%. The effect of salting, drying and subsequent storage on the histamine levels in mackerel was investigated. Increases in histamine were observed during salting, drying and storage for both whole and gutted fish, with greater increases in. general for whole fish. The increases for both whole and gutted fish occurred under conditions in which bacterial growth would be suppressed, indicating that another mechanism of histamine formation might be operative.