Factors affecting bacterial community dynamics and volatile metabolite profiles of Thai traditional salt fermented fish

Abstract

Bacterial diversity of the Thai traditional salt fermented fish with roasted rice bran or Pla-ra, in Thai, was investigated using classical and molecular approaches. Pla-ra fermentation could be classified into two types, i.e., solid-state fermentation (SSF) and submerged fermentation (SMF). Bacterial population ranged from 102-106 and 106-109 CFU/g in SSF and SMF, respectively. The rRNA detection revealed that Halanaerobium spp. and Lentibacillus spp. were the main genera present in all types and most stages of fermentation. Tetragenococcus halophillus were dominant during final stage of fermentation in the samples in which sea salt was used as one of the ingredients while Bacillus spp. were found in those that rock salt was used. In contrast, cultural plating demonstrated that Bacillus spp. were the dominant genera. B. amyloliquefaciens were the main species found in all types of Pla-ra whereas B. pumilus, B. autrophaeus, B.subtilis and B. velezensis were specifically associated with the samples in which rock salt was used. The main volatile metabolites in all Pla-ra samples were butanoic acid and its derivatives. Dimethyl disulfide was observed during earlier stage of fermentation under high salt condition with a long fermentation period. Key factors affected bacterial profiles and volatile compounds of salt fermented fish are type of salt, addition of roasted rice bran, and fermenting conditions.

Correlation between microbial community and flavour formation in dry-cured squid analysed by next-generation sequencing and molecular sensory analysis

“…There were 11 aldehydes and nine alcohols recognized in squid samples, of which the concentrations reached 425.28 and 259.51 μg/kg at the end of the process, respectively. The increase in the content of aldehyde and alcohols could be associated with fatty acids degradation and processing factors including salt, time and temperature ( Det-udom et al, 2021 ). 3-Methylbutanal (malty, caramel), heptanal (rancid, fat), methional (roast), hexanal (grass, fat), nonanal (fatty, green), 2-octenal (roast, fatty), 1-octen-3-ol (mushroom, fishy, fatty), decanal (soap, tallow) and were the dominant aldehydes.…”