Anti-polyphenol oxidase mechanism of oligomeric procyanidins and its application on browning control of “Baiyu” loquat during storage

The harvested loquat fruits are prone to browning, leading to a decline in fruit quality. Inhibiting activity of polyphenol oxidase (PPO) is an important way to prevent browning. In this study, we evaluated the inhibitory impact of oligomeric procyanidins (OPC) on hydroxylation of monophenol and oxidation of o-diphenol catalyzed by PPO and effect of OPC on loquat fruits storage. The obtained results revealed that OPC could attenuate the activity of monophenolase and diphenolase. For monophenolase activity, the inhibition rate was observed to be dose-dependent with an IC50 of 11.6 ± 3.4 μg/mL for the steady-state rate. For diphenolase activity, OPC inhibited PPO activity (IC50 = 15.75 ± 2.1 μg/mL) with a reversible and competitive mechanism and quenched fluorescence of PPO by forming OPC-PPO complex with one binding site in a static procedure. In addition, the data obtained from storage assays revealed that OPC could enhance the quality of harvested loquat fruits by attenuating the PPO activity, augmenting the content of total phenolics and flavonoids, and simultaneously delaying the browning of loquats. In this research, we identified a potent PPO inhibitor and expanded its potential as a food preservative.