Phytic Acid Delays the Senescence of Rosa roxburghii Fruit by Regulating Antioxidant Capacity and the Ascorbate–Glutathione Cycle

<i>Rosa roxburghii</i> fruit has a short postharvest shelf life, with rapid declines in quality and antioxidant capacity. This research assessed how phytic acid affects the antioxidant capacity and quality of <i>R. roxburghii</i> fruit while in the postharvest storage period and reveals its potential mechanism of action. The findings suggested that phytic acid treatment inhibits the production of malondialdehyde (MDA) and enhances the activities and expressions of glutathione peroxidase (GPX), peroxidase (POD), catalase (CAT), and superoxide dismutase (SOD) while decreasing the generation of superoxide anions (O₂^•-) and hydrogen peroxide (H₂O₂). Phytic acid treatment activates the ascorbate-glutathione (AsA-GSH) cycle and enhances the activity and expression of key enzymes in the cycle: ascorbate peroxidase (APX), glutathione reductase (GR), dehydroascorbate reductase (DHAR), and monodehydroascorbate reductase (MDHAR). It also increases the levels of non-enzymatic antioxidants, such as ascorbic acid (AsA) and glutathione (GSH), while reducing the production of dehydroascorbic acid (DHA) and oxidized glutathione (GSSG). Moreover, phytic acid treatment enhances the ratios of AsA/DHA and GSH/GSSG, maintaining the reduced state of the fruit. In summary, phytic acid improves antioxidant defense system and activates the AsA-GSH cycle, alleviating oxidative damage and ensuring <i>R. roxburghii</i> fruit quality after harvest.