High-oxygen Treatment Alleviates Browning in Postharvest Prune Fruits by Modulating Reactive Oxygen Species and Phenolic Metabolism

In this study, ‘French’ prune fruits were treated with O₂ at concentrations of 50%, 70%, and 90% and stored at 1–2 ℃ and a relative humidity (RH) of 90%–95% for up to 120 days. For comparison, air treatment was used as the control. Sampling was done every 20 days for measurement of relevant parameters to analyze the effect of highoxygen treatment on postharvest browning of prune fruits. The results showed that the high-oxygen treatments effectively inhibited browning. Among them, the 70% O₂ treatment for 6 h was the most effective, reducing the browning index by 22.06% compared with the control at the end of storage (P < 0.05). The 70% O₂ treatment significantly suppressed the activities of polyphenol oxidase (PPO) and peroxidase (POD) during storage, while maintaining the contents of total phenolics, flavonoids, and individual phenolic compounds such as caffeic acid, protocatechuic acid, and quercetin. Moreover, it enhanced the activities of superoxide dismutase (SOD) and catalase (CAT), and significantly decreased the rate of superoxide anion (O₂^-·) generation and hydrogen peroxide (H₂O₂) content. It also suppressed the increase in cell membrane permeability and malondialdehyde (MDA) content, preserving membrane stability. Consequently, the 70% O₂ treatment effectively alleviated browning in prune fruits.