Enhancing postharvest storage quality and cuticular wax composition of summer black grapes through preharvest calcium application

This study investigated the effects of preharvest calcium treatments at different developmental stages on the cuticular wax composition of <i>Summer Black</i> grapes and their correlation with fruit storage quality (4 ± 0.5 °C) and reactive oxygen species (ROS) metabolism. Calcium chloride (5 g/L) was applied at the flowering, fruit-setting, and veraison stages. Changes in cuticular wax content and composition were analyzed, along with associated indicators of storage quality and ROS metabolism. Calcium treatment increased wax content and preserved wax structure integrity during storage. Fatty acids dominated wax composition (41.38-95.64% across groups). After 60 d of storage, calcium-treated grapes showed lower weight loss and berry detachment rates and higher fruit firmness, reducing sugars, titratable acids, and protopectin content than those of the control group, with the flowering stage treatment yielding the best results. Additionally, grapes treated at the flowering stage exhibited lower levels of superoxide anion (O₂ ^·-), malondialdehyde (MDA), polyphenol oxidase (PPO), and lipoxygenase (LOX) activity and higher scavenging rates of DPPH, hydroxyl, and ABTS radicals. They also showed higher activities of antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX), and catalase (CAT), and increased levels of non-enzymatic antioxidants such as vitamin C compared to the control group, indicating the calcium treatment resulted in the highest antioxidant capacity. This study elucidates how calcium treatment maintains fruit storage quality and regulates ROS metabolism through modulation of cuticular wax composition, thereby providing a theoretical basis for improving fruit preservation.