Preparation of Isoflavones from the Tuber of Apios americana Medik. and Their Protective Effects on RIN-m5F Cells from Oxidative Damage

The intention of this study was to optimized the enrichment process of isoflavones from the tuber of Apios americana Medik. using macroporous adsorption resin and to evaluate their bioactivities. Isoflavones from the tuber of A. americana Medik. were extracted by successive hot ethanol reflux extraction and ethyl acetate extraction, and then the concentration process of isoflavones was optimized based on isoflavone concentration. The antioxidant activity and α-glucosidase inhibitory activity of the obtained isoflavone-rich fraction (AI-3) and its protective effect against oxidative damage to RIN-m5F cells were studied. The optimized processing parameters were as follows: use of D101-type macroporous resin as sorbent, sample concentration of 1.5 mg/mL, use of 80% ethanol as eluent, and eluent volume of 80 mL (the bed volume (BV) was 20 mL). The yield of AI-3 from the dried tuber of A. americana Medik. was 0.44%, and the isoflavone content was 50.83%. The half maximal inhibitory concentration (IC₅₀) of AI-3 for scavenging of 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical and 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) cation radical were 19.51 and 3.40 μg/mL, respectively, and the ferric reducing capacity was 387.83 μmol/mg. The IC₅₀ against α-glucosidase was 235.97 μg/mL. The survival rate of RIN-m5F cells treated with AI-3 at concentrations in the range of 0-300 μg/mL had no significant difference from that of the control group (P > 0.05), and AI-3 concentrations in the 25-300 μg/mL range significantly improved the survival rate of oxidatively damaged cells (P < 0.01). At 300 μg/mL AI-3 concentration, the survival rate of RIN-m5F cells was 84.19%, which was higher than that of the positive control group. D101-type macroporous resin can effectively enrich isoflavones from the tuber of A. americana Medik. yielding a fraction (AI-3) with strong antioxidant activity, α-glucosidase-inhibitory capacity and protective effect against oxidative damage to RIN-m5F cells. This study will provide a theoretical basis for the development of functional foods for the prevention of diabetes and other metabolic syndromes.