New method for evaluating bacterial reduction of trimethylamine N-oxide and its application to bacterial populations in fish muscle

摘要

Bacterial reduction of trimethylamine N-oxide (TMAO) cannot be reliably determined by qualitative methods, which are unusable because of problems relating to incubation time, the indicator and the equilibrium of the redox potential. This makes it difficult to reproduce results. These problems have been observed with various semi-agar media used in the evaluation of TMAO reduction. We propose a new and rapid method of quantitative evaluation by means of assay of trimethylarnine (TMA) in a new TMA-free culture medium. This methodology has been used to evaluate the TMAO-reducing capacity of different endogenous and exogenous bacterial strains found in fish flesh (Aeromonas hydrophila, Alteromonas communis, Escherichia coli, Flavobacterium branchiophilum, Micrococcus sedentarius, Proteus mirabilis, Pseudomonas fluorescens, Pseudomonas nautica, Serratia marcescens, Shewanella putrefaciens, Vibrio parahaemolyticus). Unlike the qualitative methods, our method showed that all tested strains were able to reduce TMAO. Fish spoilage bacteria can form TMA under anaerobic conditions, as shown by tests using bacterial suspensions from fish (Helicolenus dactyloptems, Merlangus merlangus, Clupea harengus). Such tests can be used to assess fish spoilage.