‘Tainong 1’ mango fruit were treated with hot water for 10 minutes at 55 °C and then stored at 5 °C for 3 weeks. After removal from low-temperature storage, the effects of hot water treatment (HWT) on chilling injury (CI), ripening and cell wall metabolism during storage (20 °C, 5 days) were investigated. HWT reduced the CI development of the fruit as manifested by firmer texture, external browning, and fungal lesions. A more rapid ripening process, as indicated by changes in firmness, respiration rate, and ethylene production, occurred in heated fruit after exposure to low temperature as compared with non-heated fruit. At the same time, the cell wall components in heated fruit contained more water-soluble pectin and less 1,2-cyclohexylenedinitrilotetraactic acid (CDTA)-soluble pectin than those in non-heated fruit. HWT also maintained higher polygalacturonase [enzyme classification (EC) 126.96.36.199] and β-galactosidase (EC 188.8.131.52) activities as well as lower pectin methylesterase (EC 184.108.40.206) activity. In general, the changes of ripening and cell wall metabolism parameters in the heated fruit after low-temperature storage exhibited a comparable pattern to that of non-cold-stored fruit.
Expansins are proteins that have been reported to contribute to fruit softening. In this study, an expansin gene, CDK-Exp3, was identified from persimmon fruit, and the mRNA accumulation of CDK-Exp3 during postharvest softening was examined using real-time polymerase chain reaction (PCR). Sequence analysis showed that CDK-Exp3 contained a putative open reading frame of 765 bp encoding a polypeptide of 254 amino acid residues, which had all the characteristics of α-expansin. As fruit softened, the expression of CDK-Exp3 increased dramatically within the initial 8-day ripening at 20 °C followed by a gradual decline at the late stages of ripening. The expression of CDK-Exp3 was inhibited by gibberellic acid, and the maximum transcript abundance was delayed by 20 days compared with that of the control fruit. The results suggest that CDK-Exp3 might be closely related to softening of persimmon fruit during postharvest ripening.