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.

In this study, the effects of different curing methods (static treatment, ultrasonic treatment, ultrasonic treatment combined with tumbling, vacuum tumbling and atmospheric pressure tumbling) on the textural properties, water retention and flavor quality of low-salt pre-prepared sea bass were investigated using texture analysis, scanning electron microscopy (SEM), liquid chromatography (LC) and gas chromatography-mass spectrometry (GC-MS). The results showed that tumbling alone and combined with ultrasonic treatment both significantly increased the marinade absorption rate and the mass transfer rate of sodium ion (P < 0.05), and the marinade absorption rate was 15.07% in the atmospheric pressure tumbling group, which was accompanied by reduced hardness and chewiness of fish meat. Organoleptic analysis showed that the fish treated by ultrasonic-assisted tumbling and tumbling was soft in texture, uniformly salty, and had less odor. In addition, both tumbling treatments significantly increased the total free amino acid content (P < 0.05), and the total free amino acid content was 7.395 mg/g in the atmospheric pressure tumbling group, which was about 1.24 times higher than that of the static treatment. A total of 65 volatile flavor compounds were detected across all treatment groups, among which, the contents of alcohols, esters and aromatic compounds were significantly higher (P < 0.05) in the tumbling treatment and ultrasonic-assisted tumbling groups than in the other treatment groups, suggesting that tumbling, irrespective of whether combined with ultrasonic or not, contributed to the formation of flavor substances. However, single tumbling marination showed poor water retention and water-holding capacity, and excessive tumbling might have adverse effects on fish texture. Therefore, ultrasonic-assisted tumbling was more suitable for the intensive processing of sea bass.