Biocatalytic potential of salt-stress domesticated Staphylococcus epidermidis and Lactiplantibacillus pentosus in “Yucha” fermentation

Yucha is a traditional high-salt fermented fish product whose spontaneous fermentation often leads to unstable quality and excessive biogenic amines (BAs). In this study, two salt-stress domesticated BA-degrading strains, L . pentosus ZFM94 ale-N2 and S . epidermidis FCH210 ale-N8, were developed through adaptive laboratory evolution (ALE) and evaluated for their biocatalytic potential during Yucha fermentation. Compared with the parental strains, both evolved strains showed improved salt tolerance, BA-degrading capacity and cell-envelope integrity under salt stress, while mutations in genes encoding rhamnose metabolism, D-alanylation of teichoic acids, and ABC transporters might contribute to the osmotic adaptation of ZFM94 ale-N2. In Yucha fermentation, mixed fermentation (MF) group exhibited lower total volatile basic nitrogen (TVB-N), alleviated protein oxidation, and markedly decreased BAs accumulation compared with natural fermentation (NF), ZFM94 ale-N2 fermentation (LpF), and FCH210 ale-N8 fermentation (SeF) groups. At day 28, the MF group showed the most desirable volatile profile, characterized by enhanced levels of ethanol, 1-octen-3-ol, benzaldehyde, 3-ethyl-benzaldehyde, and acetic acid. In parallel, inoculated fermentation reshaped the microbial community toward dominance of beneficial taxa ( Lactiplantibacillus , Weissella ) and induced broad metabolomic reprogramming involving amino acid, nucleotide, lipid, and transport-associated pathways, thereby promoting the formation of umami amino acids, flavor nucleotides, and unsaturated fatty acids.