Purification Optimization of Mung Bean Skin Polyphenols by Macroporous Adsorption Resin and Its in Vitro Hypoglycemic Activity

To investigate the purification process and in vitro hypoglycemic activity of mung bean skin polyphenols (MBPs), MBPs were extracted using the ultrasonic-assisted extraction method in this study. The adsorption and desorption behaviors of MBPs on eight different types of macroporous adsorption resins were examined, and the optimal resin type was selected. The purification process was optimized through single-factor experiments, and the chemical composition of the purified MBPs was identified using ultra-performance liquid chromatography-electrospray ionization quadrupole time-of-flight tandem mass spectrometry (UPLC-ESI-QTOF-MS/MS). Meanwhile, the inhibitory activities and types of MBPs on α-amylase and α-glucosidase were investigated with acarbose as the positive control. Results showed that HPD-500 resin had the best adsorption-desorption effect on MBPs. The optimized parameters of purification process were polyphenol concentration of 0.25 mg/mL, pH of 6, ethanol concentration of 80%, loading flow rate of 1 BV/h, and elution flow rate of 2 BV/h. The purity of purified MBPs was 57.23%, which was 2.55 times higher than that of the crude extract. Twelve phenolic compounds, including gallic acid, kaempferol, vitexin, isovitexin, and apigenin, were identified in the purified MBPs. The results of in vitro hypoglycemic activity study showed that MBPs had good inhibitory activities on α-amylase and α-glucosidase, with IC50 values of 98.85 μg/mL and 7.25 μg/mL, respectively, and the inhibition of MBPs against both enzymes was mixed-type inhibition. In summary, purified MBPs had good in vitro hypoglycemic activity and could be developed and utilized as functional ingredients in health foods.