Melanin resistance of heat-processed ginsenosides from Panax ginseng berry treated with citric acid through autophagy pathway

GFRS is the conversion product of Panax ginseng Meyer berry after citric acid heat treatment, which is rich in rare ginsenosides. However, the anti-melanin role of GFRS in the regulation of skin pigmentation and its material basis remains unclear. To compare the anti-melanin activity before and after citric acid heat treatment, we determined the effects of GFS and GFRS on tyrosinase activity and melanin lever under α-MSH stimulation and found the potential anti-melanin effect of GFRS. Further, Western blot and immunofluorescence methods were used to reveal the mechanism by which GFRS detects anti-melanin activity by promoting autophagy flux levels. In zebrafish models, GFRS inhibited endogenous melanin and tyrosinase better than arbutin and promoted the accumulation of autophagy levels in vivo. To determine the material basis of the anti-melanin effect of GFRS, HPLC was used to isolate and prepare 12 ginsenosides from GFRS, and their activity evaluation and structure–activity relationship analysis were performed. The results showed that the inhibitory effect of GFRS on melanin was Rg₃ > Rg₅ > Rk₁ > Rd. Molecular docking showed that their docking fraction with mushroom tyrosinase was significantly better than that of arbutin, but the presence of C-20 glycosylation decreased the anti-melanin activity of Rd. To maximize the content of Rg₃, Rg₅, and Rk₁, we optimized the process by using citric acid heat treatment of ginsenoside Rd and found that citric acid heat treatment at 100°C almost completely transformed Rd and obtained a high content of active ingredients. In summary, our data demonstrated that GFRS exerted anti-melanin effects by inducing autophagy. It was further revealed that Rg₃, Rg₅, and Rk₁, as effective active components, could be enriched by the improved process of converting ginsenoside Rd by citric acid heat treatment.