Effects of Co‐Culture Solid‐State Fermentation With <i>Kluyveromyces marxianus</i> and <i>Bacillus licheniformis</i> on the Physicochemical, Bioactive, and Flavor Properties of <i>Radix Puerariae thomsonii</i>

This study investigated the effects of solid-state fermentation (SSF) using a co-culture of Kluyveromyces marxianus and Bacillus licheniformis on the physicochemical properties, bioactive compounds, flavor profile, and free radical-scavenging activity of Radix Puerariae thomsonii (RPT). After 72 h of fermentation, the contents of total amino acids and reducing sugars significantly increased to 78.56 ± 1.87 mg/g (p < 0.001) and 204.39 ± 6.13 mg/g (p < 0.001), respectively. Compared with the unfermented control, the fermented product exhibited enhanced radical-scavenging activity and increased total phenolic and flavonoid contents. These levels peaked after 120 h of SSF at 12.46 ± 0.39 mg gallic acid equivalents (GAE)/g and 11.17 ± 0.42 mg rutin equivalents (RUT)/g, respectively. Ultra-performance liquid chromatography-orbitrap mass spectrometry (UPLC-orbitrap-MS) identified 30 bioactive compounds, with marked increases in daidzein, apigenin, and quercetin-3-β-d-glucoside, which were positively correlated with elevated α-amylase, β-glucosidase, and cellulase activities during fermentation. Among the volatile metabolites, the most abundant after 120 h were hexadecanoic acid (21.98 ± 0.62 mg/g), octadecadienoic acid (18.26 ± 0.51 mg/g), γ-sitosterol (12.47 ± 0.23 mg/g), and 2,3-butanediol (5.23 ± 0.12 mg/g). These findings demonstrate that SSF with K. marxianus and B. licheniformis enhances the functional properties of RPT, supporting its potential as a value-added ingredient for medicinal and food applications.