میثم محمدی

Chilling injury (CI), weight loss, and wrinkling are important disorders in the postharvest of sweet bell peppers. In this study, an experiment was conducted at Ilam University in 2022-2023 to evaluate the reduction of chilling injury and the extension of shelf life for red sweet bell peppers. The experiment followed a split-plot design with three replications. The subfactor involved different concentrations (0, 1, 5, 10, and 15 mM) of oxalic acid (OA), which were applied to red sweet bell pepper plants of the "Westland" variety at 3 and 6 days before harvesting. The main factor focused on examining various fruit traits at harvest time, as well as after 12 and 24 days of storage at 4°C. The results indicated that as the storage time increased, the rate of CI also increased while the quality of the fruits decreased. However, treatment with OA reduced the CI index and increased the shelf life of pepper fruits during postharvest storage. Specifically, treatment with a concentration of 10 mM OA resulted in decreased levels of hydrogen peroxide, proline, electrolyte leakage, malondialdehyde, lipoxygenase activity, phospholipase D activity, and polyphenol oxidized enzymes due to glycine betaine accumulation. Furthermore, this treatment helped preserve phenolic compounds, vitamin C content, and antioxidant capacity in sweet bell pepper fruits. The activity of antioxidant enzymes such as catalase, superoxide dismutase, and ascorbate peroxidase also increased in OA-treated fruits compared to control samples. These factors contributed to the reduction of CI in pepper fruits during postharvest. Additionally, the activity of phenylalanine ammonia-lyase enzyme along with antioxidant enzymes was higher in treated fruits compared to control samples. On the other hand, the activity of NADPH oxidase enzyme was lower in OA-treated fruits than in control fruits. This result suggests that OA treatment helps maintain energy levels (ATP) in treated fruits during storage. Overall, these findings demonstrate that OA treatment can accumulate glycine betaine osmolyte within fruit tissues. This reduces damage caused by reactive oxygen species and helps maintain antioxidant capacity and energy levels during storage. As a result, OA treatment can effectively decrease CI and enhance the shelf life of sweet bell pepper fruits. Based on these results, it is recommended to use a concentration of 10 mM OA during the production process for sweet bell peppers to decrease CI and increase their shelf life.