Enhancement of Apostichopus japonicus peptide flavor through bacterial and enzyme co-fermentation (BECF) and the identification of novel antioxidant peptides in the fermented product

In this study, we optimized the BECF process parameters by single-factor experiments and response surface methodology (RSM). Additionally, various analytical techniques were employed to determine the volatile flavor compounds, amino acid composition, and peptide sequences of the fermented product. The antioxidant activities of 10 peptides were evaluated via free radical scavenging assays. The results indicated that the optimal BECF conditions for <i>Apostichopus japonicus</i> body wall (AJBW) were as follows: 2.3 % bacterial inoculum, fermentation for 31 h at 30 °C, 463 U/g enzyme dosage, and enzymatic hydrolysis at 50 °C for 4 h. Gas chromatography-ion mobility spectrometry analysis revealed a significant reduction in aldehydes, which impart a pungent odor, in the co-fermented product (AJM) as compared to the control. While the content of alcohols, ketones, and esters, which contribute to aromatic flavors, was significantly increased. The content of essential amino acids in AJM, as analyzed through an automatic amino acid analyzer, was slightly higher compared to that in AJBW. Liquid chromatography-tandem mass spectrometry identified a total of 808 sea cucumber peptide fragments with high confidence. DPPH, ABTS, and hydroxyl radical scavenging assays revealed that peptides LFW and LFPW exhibited the strongest antioxidant activities. Molecular docking studies showed significant hydrogen-bonding interactions. In conclusion, BECF is an effective strategy for enhancing the flavor of <i>A. japonicus</i> peptide.