Effects of postharvest treatment with pullulan, calcium chloride, and chitosan on quality and sugar metabolism of Annona squamosa during storage

In this study, the effects of postharvest treatment with 1% pullulan, 2% calcium chloride, and 1% chitosan on the physiological and biochemical properties, enzymatic activities and the differentially expressed genes (DEGs) with sucrose metabolism of Annona squamosa L. fruits stored at 15 +/- 1 degrees C for 12 days were investigated. Exogenous substances treatment retained a higher level of firmness, surface color, total soluble solids, organic acids, and tvolatile flavor substances compared to the control fruit. Exogenous substances treatments, particularly calcium chloride, enhanced sucrose phosphate synthase activity, whereas it inhibited acid invertase (AI) and neutral invertase (NI) activities. These changes in enzyme activities together resulted in a significantly higher sucrose content and lower glucose and fructose contents. The number (1550 genes), proportion (6.46%), and expression levels of DEGs in the calcium chloride-treated fruit, which was enriched in the starch and sucrose metabolism pathways, were all significantly higher than in chitosan treatment. The findings indicated that exogenous calcium chloride might alter sucrose metabolism during fruit ripening by regulating the enzymatic activities and metabolism pathway. This will provide a theoretical basis for further research on the regulation of sugar metabolism by exogenous substances treatment to solve the problem of quality degradation in the storage of A. squamosa. Novelty impact statement This study indicated that the application of chitosan, pullulan, or calcium chloride, especially calcium chloride treatment, can effectively maintain the quality of Annona squamosa fruit during storage. It was found that exogenous calcium chloride might alter sucrose metabolism during fruit ripening by regulating the enzymatic activities and metabolism pathway. The results provided a theoretical basis for exploring the mechanism of exogenous substances for maintaining the postharvest quality and enhancing the shelf life of A. squamosa fruit in further research.