Biogenic amine formation and degradation by potential fish silage starter microorganisms

Abstract

Fish waste can be advantageously upgraded into animal feed by fermentation with lactic acid bacteria (LAB). This procedure is safe, economically advantageous and environment friendly. The pH value of the fish pastes decreases to below 4.5 during ensilage. This pH decrease is partly responsible for preservation. Decreased pH values and relatively low oxygen concentrations within the silage facilitate decarboxylase activity. Biogenic amines may constitute a potential risk in this kind of product since their precursor amino acids are present in fish silage. It is of great importance to ensure that the LAB strains chosen for starters do not produce biogenic amines. Some bacteria, among which some LAB species, are able to degrade these metabolites by means of amino oxidases. This could be of interest for fish silage production, to control biogenic amine build-up in this product. Seventy-seven LAB cultures isolated from fish pastes submitted to natural fermentation at two temperatures (15 and 22°C) and selected combinations of these isolates were examined for histamine, tyramine, cadaverine and putrescine production. Of the isolates tested, 17% were found to produce one or more of these biogenic amines. The behaviour of diamine oxidase was tested under the conditions present in fish silage. Addition of 12% sucrose or 2% NaCl did not affect histamine degradation. Addition of 0.05% cysteine decreased histamine degradation. Degradation occurred at all temperatures tested (15, 22 and 30°C), but not at pH 4.5. Forty-eight potential fish silage starters were tested for histamine degradation in MRS broth containing 0.005 g l −1 histamine and incubated at 30°C. Indications were found that five of these isolates could degrade as much as 20–56% of the histamine added to the medium within 30 h, when used as pure cultures. No histamine degradation was observed with combinations of cultures. Histamine degradation (50–54%) by two of these isolates was also observed in ensiled fish slurry.