Effects of Exogenous Melatonin on Storage Quality and Cell Wall-Degrading Enzymes of ‘Nanguo’ Pears

This study was undertaken to investigate the effects of exogenous melatonin on the activity and gene expression of cell wall-degrading enzymes and quality attributes (including mass loss rate, ethylene release rate and surface color) of ‘Nanguo’ pears during storage at room temperature. The results demonstrated that exogenous application of melatonin maintained higher flesh firmness, chlorophyll content and soluble solid content, remarkably decreased ethylene release rate, and delayed peel yellowing and the decrease in titratable acid content, but did not affect the mass-loss rate of ‘Nanguo’ pears. Moreover, melatonin treatment significantly retarded the degradation of water-insoluble pectin and the accumulation of water-soluble pectin. Compared with the control group, the most significant difference in the contents of water-insoluble and water-soluble pectin in the melatonin group appeared on days 3–12 and 6–12 (P < 0.05), respectively. On day 9, the content of water-soluble pectin in the control group was 1.18 times higher than that in the melatonin group, while the content of water-insoluble pectin in the melatonin group was 1.21 times higher than that in the control group. The changes of the content of pectin substances were related to the inhibition of melatonin on polygalacturonase (PG), pectin methylesterase (PME), β-glucosidase (β-glu), cellulase (Cx) activities and gene expression. These results demonstrated that exogenous application of melatonin could maintain the fruit quality of ‘Nanguo’ pears by inhibiting the activity and gene expression of cell wall-degrading enzymes and ethylene release.