Gallic and ferulic acids suppress proteolytic activities and volatile trimethylamine production in the food‐borne spoiler Rahnella aquatilis KM05

BACKGROUND: Rahnella aquatilis is a recognised microbial threat that alters the sensory properties of seafood. The highfrequency with which R. aquatilis is isolated from fish has prompted a search for alternative preservatives. In the present study,in vitro and fish-based ecosystem (raw salmon-based medium) approaches were used to validate the antimicrobial effects ofgallic (GA) and ferulic (FA) acids against R. aquatilis KM05. The results were compared with data describing the response ofKM05 to sodium benzoate. Bioinformatics data of the whole genome were used to analyse the potential for fish spoilage byKM05 in detail, and the results revealed the main physiological characteristics that underlie reduced seafood quality.RESULTS: In the KM05 genome, the most abundantly enriched Gene Ontology terms were ‘metabolic process’, ‘organic sub-stance metabolic process’ and ‘cellular process’. Through an evaluation of the Pfam annotations, 15 annotations were foundto be directly involved in the proteolytic activity of KM05. Peptidase_M20 was the most abundantly represented (abundancevalue of 14060). Proteins representing the CutC family (abundance value of 427) indicated the potential for KM05 degradationof trimethyl-amine-N-oxide. Subinhibitory concentrations of GA and FA suppressed the proteolytic activities of KM05 bothin vitro and in RS medium by an average of 33–45%. These results were confirmed by quantitative real-time PCR experiments,which also showed that the expression levels of genes involved in proteolytic activities and volatile trimethylamine productionwere also decreased