Appealing smoky flavor formation and flavor quality enhancement in soy sauce: Synergistic ferulic acid metabolism by a yeast consortium (Starmerella etchellsii, Wickerhamiella versatilis, Debaryomyces hansenii).

Soy sauce, a traditional condiment, derives its characteristic smoky aroma from 4-vinylguaiacol (4-VG) and 4-ethylguaiacol (4-EG), formed by yeast metabolism of ferulic acid (FA). However, controlling the production of these compounds remains challenging. This study isolated four yeasts from soy sauce: Starmerella etchellsii was identified as a key 4-VG producer (28.33 mg/L in monoculture), Wickerhamiella versatilis converted 4-VG to 4-EG, while Debaryomyces hansenii degraded FA/4-VG. Critically, Zygosaccharomyces rouxii showed no FA metabolic capability. Atmospheric and room temperature plasma (ARTP) mutagenesis of S. etchellsii generated mutant WQF-S15 with 86.2 % higher 4-VG yield (72.32 mg/L). Sequential inoculation of WQF-S15 followed by W. versatilis during soy sauce fermentation significantly elevated smoky compounds (4-EG: 26.90 mg/L) and optimized amino acid nitrogen to 0.98 g/100 mL. Sensory and chromatographic analyses confirmed enhanced caramel aroma in S15 + W(A) (4-hydroxy-2,5-dimethyl-3(2H)-furanone (HDMF) increased 3.04-fold vs. control), while W. versatilis enhanced ester complexity. Synergistic yeast action thus improved flavor quality.