The effect of marinating on quality of rainbow trout fillet strips

Marinades containing salt, sugar, and organic acids are increasingly used to manufacture modern fish products that are sold raw and intended to be cooked by consumers. In corresponding meat products, marinating is known to have a major effect on the composition of spoilage microbiome but the effect of commercial marinating on bacterial diversity and amine production in modified atmosphere-packaged (MAP) fish had not been extensively studied. This knowledge gap prompted our study about the microbial ecology and amine constitution in MAP rainbow trout of two manufactireres. In general, marination increased the maximum concentrations (7-8 log cfu/g) of psychrotrophic bacteria by one logarithmic unit. According to the 16S rRNA gene amplicon sequence analyses, lactic acid bacteria (LAB) predominated in the marinated strips one day after use-by date. In unmarinated strips, either LAB or gram-negative bacteria, such as Fusobacterium and Shewanellaceae, dominated depending on the manufacturer. Latilactobacillus fuchuensis was the prevailing LAB species in both marinated and unmarinated strips according to the culture-dependent numerical analysis of ribopatterns. In addition, Leuconostoc gelidum and Lactococcus carnosus were common in the marinated and unmarinated strips, respectively. Amine levels measured by LC-MS and GC-MS showed marked differences in tyramine and trimethylamine (TMA) levels/concentrations between the marinated and unmarinated strips. Higher tyramine levels/concentrations (5 fold) were associated with the marinated strips whereas TMA levels were higher (20 fold) in the unmarinated strips. We also screened if the prevailing species L. fuchuensis, is able to produce tyramine and obtained positive reactions for a subset of isolates tested. Our results indicate that marinating may increase tyramine levels.