Abstract: Post-harvest Huangguan pear was treated with calcium chloride and chitosan coating and the citrate metabolic regulation mechanism and the citric acid metabolism under different treatments during cold storage were investigated. Huangguan pear was soaked with calcium chloride followed by chitosan coating treatment. The level of citric acid was determined using HPLC and the activity of citric acid metabolizing enzymes such as citrate synthase (CS), cytoplasmic aconitase (cyt-ACO) and isocitrate dehydrogenase (NADP-IDH) were also monitored. Real-time PCR was employed to analyze the relative expression levels of citric acid metabolizing enzyme genes. Statistical analysis on correlation among citric acid, metabolizing enzyme and related genes were conducted. Both treatments could significantly prevent the decline of citric acid content and improve the activity of enzymes. Calcium chloride and chitosan treatments can affect the gene expression in certain extent. CS had important influence in citric acid accumulation. The correlation analysis showed that there was a significant correlation between the content of citric acid and the activity of CS. A significant positive correlation were observed between citric acid and the activity of cyt-ACO in pulp whereas the correlation was negative in Huangguan peel. NADP-IDH showed slight effect on the metabolism of citric acid. Gene expression wasconsistent with the changes in the corresponding enzyme activity and thereby regulate the citric acid metabolism. In summary, the metabolism of citric acid in postharvest Huangguan pear was co-regulated by enzyme activity and related gene expression. Calcium chloride and chitosan coating treatments can affect the activity of the enzymes and the expression level of related genes.

Key words: citric acid, metabolizing enzyme, gene expression, coating treatment