Synergistic Flavor Modulation and Functional Enhancement of Douchiba via Compounding with Bacillus subtilis-Fermented Adlay

Traditional Douchiba (DCB), a bacterial-type fermented soybean condiment, suffers from pronounced bitterness and limited functional attributes, hindering its broader application. To address these challenges, this study innovatively compounded matured <i>Bacillus subtilis</i>-fermented adlay (BFA) with DCB at varying ratios to develop a fermented adlay-DCB seasoning (FADS). Key physicochemical, nutritional, functional, and sensory parameters were systematically analyzed, and a multidimensional quality evaluation system was established via the Entropy Method for composite scoring. Results revealed that BFA integration enhanced the brightness and increased the content of total triterpenoid (by 16-fold) and γ-aminobutyric acid (by 9-fold) in FADS. Notably, electronic tongue analysis demonstrated that BFA significantly reduced the bitterness, after-bitterness, and saltiness intensities of DCB, achieving maximum reductions of 90.12% for bitterness and 87.63% for after-bitterness. Meanwhile, GC-MS profiling identified 89 volatile compounds, with pyrazines, alcohols, and acids as the primary volatile components in FADS. Additionally, the S4 sample (the BFA:DCB ratio = 6:4) achieved the highest composite score (0.64), with pyrazines contributing 0.13 points to the evaluation. In summary, BFA not only significantly mitigated bitterness in DCB but also substantially enhanced its bioactive properties. The results offer a scientific basis for the flavor improvement of fermented seasonings.