Production of histamine and tyramine by bacteria isolated from Portuguese vacuum-packed cold-smoked fish

Abstract

An agar medium containing histidine or tyrosine incubated anaerobically was used for detecting the decarboxylating activity of bacteria isolated from Portuguese vacuum-packed cold-smoked fish during chilled storage. The capacity of each bacterial isolate to produce histamine and tyramine was studied at 25 and 5 degreesC incubated for 48 h and 10 days, respectively. More strains produced histamine and tyramine at 25 degreesC cornpared with 5 degreesC although lactic acid bacteria (LAB) strains exhibited similar results at the two different temperatures. Tyramine was produced by majority of the isolates tested although very low concentrations were produced at 5 degreesC as confirmed by high-pressure liquid chromatography (HPLC. Tyrosine-agar was shown to be a good indicator medium for detection of bacteria that produced high levels of tyramine, since typical colonies surrounded by a translucent halo were easily recognised. LAB identified as Le. Lactis lactis 1 and Carnobacterium divergens were detected as tyramine-producing bacteria. Acinetobacter spp. and Pseudomonas spp., isolated from all Portuguese smoked fish products, were negative on histidine-agar, but HPLC identified considerable quantities of histamine produced in a broth medium.