Cinnamon Essential Oil–Chitosan Composite Coating Delays Fruit Softening in Actinidia arguta by Inhibiting Cell Wall Metabolism

Actinidia arguta fruits are highly perishable due to their thin, glabrous skin and high respiration rate. The primary objective of this study was to investigate the effects of a coating composed of 1.2% cinnamon essential oil (CEO) combined with 1% chitosan (CH) on the storage quality, cell wall structure, and cell wall metabolism in A. arguta fruits after subjecting them to 25 ± 1 and 4 °C. Results showed that this coating composition effectively maintained fruits’ postharvest appearance and firmness, reduced the rate of weight loss, and preserved the fruit’s original sensory flavor. Furthermore, the coating treatment significantly delayed the conversion of protopectin to soluble pectin, the increase in cellulose content, and the decrease in acid-insoluble solid (AIS) content. Furthermore, low activities of polygalacturonase (PG), pectin methylesterase (PME), pectin lyase (PL), cellulase (Cx), β-glucosidase (β-Glu), and β-galacturonidase (β-Gal) were found in the treatment during storage. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observed that the composite coating treatment strongly maintained the integrity of fruit cell wall structure and exhibited positive effects under room temperature conditions, with its protective effects further enhanced and prolonged under refrigerated conditions. In conclusion, this combination treatment extended the postharvest storage life of A. arguta, possibly by inhibiting cell wall degradation, maintaining fruit firmness, and regulating the activity of cell wall metabolism.