Effect of folic acid on mitigation of chilling injury and extending quality and shelf life of eggplant stored under prolonged low temperature

Chilling injury (CI) is a primary limiting factor in the cold storage of eggplants ( Solanum melongena L.), leading to rapid pericarp browning and quality deterioration. This study investigated the efficacy of folic acid (FA), a vital cofactor in carbon metabolism, as a novel postharvest strategy for alleviating CI and extending the marketable life and quality of eggplants during refrigeration. Freshly harvested eggplants were treated with FA at varying concentrations (0, 1.5, 3.0, 4.5, and 6.0 mg/L) and stored at 4°C for 30 d. Every five days, the eggplants were subjected to various physicochemical and enzymatic analyses. The results demonstrated that FA application significantly delayed the onset of CI symptoms, effectively suppressing weight loss, electrolyte leakage, and malondialdehyde (MDA) accumulation in the tested samples. Enzymatic analysis revealed that FA treatment, particularly at 6.0 mg/L, modulated the enzymatic balance between oxidative defense and browning in the tested eggplants. Treatment maintained high activities of superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX), thereby reducing the oxidative stress burden under cold stress. Simultaneously, FA suppressed the activities of browning-related enzymes, polyphenol oxidase (PPO), and peroxidase (POD). Furthermore, FA upregulated phenylalanine ammonia-lyase (PAL) activity, leading to the preservation of total phenolics and flavonoids, which contributed to sustained non-enzymatic antioxidant capacities and radical-scavenging abilities (DPPH, ABTS, and FRAP). Principal component and Pearson correlation analyses confirmed that the FA-treated fruit maintained a biochemical profile distinct from that of the control samples. Among the tested FA treatments, eggplants treated with above 4.5 mg/L exhibited an excellent prevention effect from chilling injury. Overall, these findings suggest that FA mitigates CI by preserving membrane integrity and coordinating the antioxidant defense system, thereby offering a safe and effective approach to extend the shelf life of chilling-sensitive produce.