Metals/bisulfite system involved generation of 24-sulfonic-25-ene ginsenoside Rg1, a potential quality control marker for sulfur-fumigated ginseng

Ginseng is a most popular health-promoting food with ginsenosides as its main bioactive ingredients. Illegal sulfur-fumigation causes ginsenosides convert to toxic sulfur-containing derivatives, and reduced the efficacy/safety of ginseng. 24-sulfo-25-ene ginsenoside Rg1 (25-ene SRg1), one of the sulfur-containing derivatives, is a potential quality control marker of fumigated ginseng, but with low accessibility owing to its unknown generation mechanism. In this study, metals/bisulfite system involved generation mechanism was investigated and verified. The generation of 25-ene SRg1 in sulfur-fumigated ginseng is that SO2, formed during sulfur-fumigation, reacted with water and ionized into HSO3−. On the one hand, under the metals/bisulfite system, HSO3− generates HSO5− and free radicals which converted ginsenoside Rg1 to 24,25-epoxide Rg1; on the other hand, as a nucleophilic group, HSO3− reacted with 24,25-epoxide Rg1 and further dehydrated to 25-ene SRg1. This study provided a technical support for the promotion of 25-ene SRg1 as the characteristic quality control marker of sulfur-fumigated ginseng. [Display omitted] •HSO3−, O2 and metals take part the generation of 24-sulfonic-25-ene Rg1 (25-ene SRg1).•HSO3−, O2 and metals in sulfur-fumigated ginseng composed metals/bisulfite system.•Metals/bisulfite system generates oxysulfur radicals and HSO5− in fumigated ginseng.•Oxysulfur radicals and HSO5− oxidized Rg1 to 24,25-epoxide Rg1 during fumigation.•Epoxide Rg1 reacted with HSO3−, and further dehydrated to generate 25-ene SRg1.