Characterization of microbiological and physicochemical changes in traditional Thai pla ra during two-stage fermentation of snakehead fish (Channa striata)

Abstract

The present study examines the microbiological and physicochemical transformations occurring during the traditional fermentation of pla ra, an ethnic fermented fish product popular in northeastern Thailand (Isan region). Utilizing a two-stage fermentation process—initial salting of snakehead fish (Channa striata) for three months followed by the addition of rice bran for an additional three months—changes in microbial communities and biochemical properties were systematically analyzed. In the early stages of fermentation, halophilic bacteria such as Pediococcus and Tetragenococcus predominated, whereas the addition of rice bran promoted the growth of Lactobacillus in later stages. Fungal species, including Saccharomyces, Candida, and Aspergillus, exhibited increased abundance during the second stage, contributing to the flavor complexity and sensory profile of pla ra. Biochemical modifications observed during pla ra fermentation included a decline in pH, accumulation of protein and lipid degradation products, and increased lipid oxidation. Correlation analysis showed that Lactobacillus and Aspergillus were the most dominant microorganisms contributing to pH, protein hydrolysis, and lipid degradation during fermentation. All the microbial and biochemical processes induced physical changes, including softening of fish muscle and progressive browning of the product. A further organoleptic liking test using untrained panelists demonstrated that the incorporation of pla ra fermented with rice bran enhanced panelists’ acceptance of som tum, a traditional Thai green papaya salad. The findings generated from this study could serve as a foundation for further studies on pla ra and its integration into international culinary and scientific contexts.