The aim of this study was to determine the interrelationship between umami peptides and microorganisms in traditional fermented sea bass and to explore the inhibitory effect of umami peptides on bitterness. Thirty-eight umami peptides were identified and predicted from traditional fermented sea bass using peptidomics combined with machine learning techniques, and the results of macrogenomic annotation indicated that a total of 51 microbial genera and 7 proteases were involved. Rhodococcus, Staphylococcus, Clostridium, Thiothrix, Pseudomonas and Achromobacter might play key roles in the formation of the flavor peptides in fermented sea bass. Molecular docking results showed that umami peptides EEEVVEEVE, DEEYPDL and DEEYPDLS could bind to the bitter taste receptor (TAS2R14), and their binding cavities were consistent. The interaction between the three peptides and TAS2R14 was mainly through hydrogen bonding, and the key binding sites of these peptides were SER265, SER69, SER65 and THR86. The electronic tongue results showed that all three umami peptides had a significant inhibitory effect on bitterness. This study provides a new idea to study the interaction between fish-derived umami peptides and bitterness.

Inoculated fermentation enables rapid fermentation of aquatic products. No studies have been conducted on the lipid profiles of inoculated fermented golden pompano (Trachinotus ovatus). In this study, a lipase-producing Bacillus subtilis with salt tolerance was screened from traditionally fermented golden pompano (TF) and used as a starter culture. Whole-genome sequencing analysis revealed it carries 4 clustered regularly interspaced short vpalindromic repeats structures and 2 genes encoding triacylglycerol lipase. Untargeted lipidomics identified lipid molecules (833) in 6 major classes from B. subtilis SCSMX-2 fermented golden pompano (IF). A total of 28 lipid molecules were upregulated in IF, including phosphatidylcholines (PCs), triacylglycerols (TAGs), and lysophosphatidylcholine. B. subtilis supplementation enhanced the production of polyenyl PCs and medium- and long-chain TAGs. The IF rich in linoleic, docosahexaenoic acids (DHA), and eicosapentaenoic acid were primarily distributed in the sn-2 position of DHA, PC and phosphatidylethanolamine. This research revealed the lipid profiles of IF, providing theoretical basis for the application of B. subtilis in the fermented fish industry.

Popular fermented golden pomfret (Trachinotus ovatus) is prepared via spontaneous fermentation; however, the mechanisms underlying the regulation of its flavor development remain unclear. This study shows the roles of the complex microbiota and the dynamic changes in microbial community and flavor compounds during fish fermentation. Single-molecule real-time sequencing and molecular networking analysis revealed the correlations among different microbial genera and the relationships between microbial taxa and volatile compounds. Mechanisms underlying flavor development were also elucidated via KEGG based functional annotations. Clostridium, Shewanella, and Staphylococcus were the dominant microbial genera. Forty-nine volatile compounds were detected in the fermented fish samples, with thirteen identified as characteristic volatile compounds (ROAV > 1). Volatile profiles resulted from the interactions among the microorganisms and derived enzymes, with the main metabolic pathways being amino acid biosynthesis/metabolism, carbon metabolism, and glycolysis/gluconeogenesis. This study demonstrated the approaches for distinguishing key microbiota associated with volatile compounds and monitoring the industrial production of high-quality fermented fish products.