Ultrasound-assisted and resin-based purification of bioactive polyphenols from peony (Paeonia ostii) pods: process optimization and α-glucosidase inhibitory activity

The valorization of agricultural by-products into high-value ingredients requires efficient and green extraction technologies. Ultrasonic-assisted extraction (UAE) has emerged as a promising technique for this purpose due to its efficiency and environmental benefits. In this study, an integrated green process was developed for recovering bioactive polyphenols from peony (Paeonia ostii) pods (PPP), an underutilized by-product, using combined UAE and macroporous resin purification. The ultrasonication process was systematically optimized via response surface methodology. The determined optimal conditions (46 % ethanol, 14 mL/g liquid-solid ratio, 60 min ultrasonication) achieved a yield of PPP of 52.17 ± 0.06 mg GAE/g DW. Subsequent purification employing D101 macroporous resin and 40 % ethanol elution produced a refined polyphenol fraction, PPP40, with a purity of 43.93 %. Untargeted metabolomic profiling revealed 17 major phenolic constituents in PPP40, including gallic acid, kaempferol 7-O-glucoside, isorhamnetin-3-glucoside-4'-glucoside, and ethyl gallate as predominant compounds. The functional efficacy of the purified PPP40 fraction was evaluated based on its α-glucosidase inhibitory activity. PPP40 exhibited potent inhibition, with an IC₅₀ value of 639.96 ± 4.57 μg/mL, and acted via a mixed-type inhibition mechanism. Multi-spectroscopic analyses elucidated that the inhibitory mechanism involved dynamic fluorescence quenching and concomitant conformational changes in α-glucosidase. The proposed integrated ultrasound-resin process offered an efficient and sustainable strategy for valorizing agricultural by-products, yielding a well-characterized and polyphenol-enriched fraction with potential application as a functional food ingredient for regulating postprandial blood glucose management.