Enzymatic Bioconversion for Ginsenoside Rd Enrichment in Red Ginseng Extract: Process Optimization and Biological Evaluation

Ginsenoside Rd is a protopanaxadiol-type ginsenoside with potential as a value-added ginseng-derived compound. This study developed an enzymatic process for selective enrichment of Rd from major precursor ginsenosides in red ginseng extract (RGE). Five commercial enzyme preparations were screened, and Frontia® Fiber Wash was selected based on its ability to promote Rd formation while limiting further deglycosylation. Transformation of Rb1, Rb2, and Rc toward Rd was confirmed using individual substrates. Six reaction variables were screened using a factorial design, identifying reaction temperature, RGE concentration, and reaction time as the major factors. These variables were optimized using a Box–Behnken design and response surface methodology. Numerical optimization predicted optimum conditions of 0.882% (w/v) RGE, 52.4 °C, and 14.3 h, with a relative Rd content of 95.77%; experimental validation yielded 95.54%. The optimized bioconverted RGE increased collagen synthesis in human dermal fibroblasts to 121.59% of the untreated control and inhibited LPS-induced nitric oxide production in RAW264.7 macrophages by 81.23% at 100 μg/mL. These findings demonstrate that commercial enzyme screening combined with statistical process optimization enables selective Rd enrichment from a complex red ginseng matrix and suggest that enzymatic bioconversion may also modulate the biological properties of RGE.