Purification, Composition and in Vitro Hypoglycemic Activity of Plum Pomace Polyphenols

To reduce resource waste in the processing of agricultural products and promote the high-value utilization of by-products, this study optimized the purification conditions of plum pomace polyphenols (PPPs). The components of PPPs were identified using ultra-high performance liquid chromatography-electrospray ionization quadrupole time-of-flight-tandem mass spectrometry (UPLC-ESI-QTOF-MS/MS), and the inhibitory effects of PPPs on α-amylase and α-glucosidase were evaluated in vitro. Molecular docking was used to analyze the interaction mechanisms between the characteristic polyphenols and the two enzymes, thereby elucidating the hypoglycemic mechanism of PPPs. The results showed that after optimization, the purity of the isolated PPPs increased by 98% compared with the crude extract. The purified PPPs contained over 30 polyphenolic compounds including flavonoids, phenolic acids, anthocyanins, and lignans, demonstrating significant hypoglycemic potential. PPPs exhibited strong inhibitory effects on both α-amylase and α-glucosidase, with half-maximal inhibitory concentration values of (91.34 ± 0.77) and (27.64 ± 0.72) μg/mL, respectively. The inhibition types were identified as mixed competitive-noncompetitive inhibition for α-amylase and mixed uncompetitive-noncompetitive inhibition for α-glucosidase. Molecular docking results revealed that the characteristic polyphenols chlorogenic acid and rutin could stably bind to the key amino acid sites of both enzymes through hydrogen bonding, with binding energies of -8.0 and -7.9 kcal/mol for α-amylase, and -8.4 and -10.3 kcal/mol for α-glucosidase, respectively. This study further elucidated the inhibitory mechanism and selective tendency of PPPs against the two carbohydrate-digesting enzymes. The findings of this study provide a solid theoretical basis and technical support for the further development and utilization of plum by-products.