Optimization of Macroporous Resin Purification Process and in Vitro Activity Study of Total Flavonoids from Citrus reticulata cv. Ponkan Peel

To investigate the desirable purification process of ponkan Chenpi flavonoids (PCf) and their in vitro antioxidant and hypoglycemic activities, this study extracted PCf using ultrasound-assisted solvent extraction. Four types of macroporous resins were evaluated for their static adsorption-desorption efficiency toward PCf, and HPD-500 resin was identified as the optimal carrier. Single-factor experiments were subsequently conducted to optimize the purification parameters. The antioxidant activity of PCf (before and after purification) were assessed using DPPH radical scavenging rate, ABTS⁺ radical scavenging rate, and ferric ion reducing capacity. The α-glucosidase inhibitory activity was evaluated. Results demonstrated that HPD-500 resin achieved the highest purification efficiency for PCf under optimized conditions: 2 of pH, 80% ethanol concentration, sample loading flow rate of 4 mL/min, elution flow rate of 3 mL/min, and a sample-to-eluent volume ratio of 1:1.6. Post-purification, the reducing sugar content of PCf was significantly reduced, while the total flavonoid content increased (132.2±9.62 mg RE/g DW). Purified PCf exhibited stronger antioxidant and hypoglycemic activities, with 93.75%±0.82% of ABTS⁺ radical scavenging rate reaching, 77.42%±0.91% of DPPH radical scavenging rate, double ferric ion reducing capacity, and 66.84%±0.67% of α-glucosidase inhibitory rate. In summary, HPD-500 resin is suitable for the preliminary separation and purification of ponkan Chenpi flavonoids, and the purified substance demonstrates significant antioxidant activity and inhibitory effect of α-glucosidase, providing a valuable reference for the further development of ponkan Chenpi-based functional products.