Effects of melatonin treatment on the physiological quality and cell wall metabolites in kiwifruit

Abstract We investigated the effects of melatonin (MT) treatment on the physiological quality and cell wall metabolism of kiwifruit during a 12-day shelf life period (20 ± 1 °C, 90 ± 5% RH), after 90 days of cold storage (0 ± 0.5 °C, 90 ± 5% RH). Our results showed that MT treatment delayed kiwifruit softening, as evidence by the enhanced endurance of a healthy appearance, quality, color difference L* value, and firmness of the fruit flesh. MT treatment reduced fruit decay rate, respiration rate, and malondialdehyde content; furthermore, MT-treated kiwifruit maintained high levels of total soluble solids, titratable acid, and ascorbic acid. Additionally, MT inhibited the decrease in fruit pectin, cellulose, and hemicellulose contents; it delayed the increase in water-soluble pectin content and kept pectin methyl esterase, polygalacturonase, cellulase, and β-galactosidase activities low. These results indicated that melatonin may have reduced the speed of softening of kiwifruit and preserved fruit quality by inhibiting enzymatic degradation of the cell wall, and by delaying pro-pectin, cellulose, and hemicellulose degradation, as well as the increase of water-soluble pectin content. These findings indicate that MT treatment may be an effective measure to delay kiwifruit postharvest cell-wall metabolism and preserve fruit quality.