Influence of postharvest citric acid and chitosan coating treatment on ripening attributes and expression of cell wall related genes in cherimoya (Annona cherimola Mill.) fruit

We investigated the effects of citric acid and chitosan coating on the fruit ripening attributes of cherimoya (Annona cherimola Mill.) stored at 15 +/- 1 degrees C for 10 days. Compared to the controls, a combined treatment of citric acid and chitosan coating delayed the browning, splitting, and decay, maintained firmness, and inhibited the increase in respiration rate of the cherimoya fruits. The inhibition of softening and splitting was associated with decreases in the activities of pectin methylesterase and polygalacturonase and solubilization/degradation of pectin ensued. The citric acid and chitosan coating treatment delayed the softening and splitting of the harvested cherimoya fruits by regulating the CMCase activity and starch sugar conversion. Throughout the storage period, the citric acid and chitosan coating treated cherimoya fruits also exhibited a lower polyphenol oxidase activity and higher superoxide dismutase, peroxidase, and catalase activities compared with the controls. Moreover, the production of superoxide free radicals and content of malondialdehyde were significantly declined in the treated fruits. Furthermore, the expression patterns of several cell wall-related genes in cherimoya were analyzed by quantitative real time PCR. The data showed that all these genes, including three AcXETs, three AiEXPs and one AcPE, exhibited highly diversified expression patterns during the fruit softening. AcXET1 and AcKET2 showed highest expression levels on the time points 6-d and 8-d, while the accumulation of AcEXP3 notably increased on the time point 6-d. The citric acid and chitosan coating treatment delayed the accumulation of AcXEP1, AcEXP1, AcEXP1 and AcPE by reducing their mRNA levels. Our findings suggest that treatment with 20.0 mM citric acid combined with 1.00% chitosan can provide an effective approach to maintain postharvest quality and extend the shelf life of cherimoya. (C) 2015 Elsevier B.V. All rights reserved.