Study On The Change Of Organic Acid And Regulation Of Metabolizing Enzyme In Post-harvest Huangguan Pear Fruit

In this research, Huangguan pear after harvested was treated by 2% calcium and coated with 1% pullulan. The paper focused on the effect of different treatments on organic acid metabolism in pear fruit during storage. The contents of citrate acid and malic acid and their relative enzyme activities of pear fruit were assayed. The key enzymes of pear after harvested citrate acid and malic acid metabolism were determined. It provided the basis for the further elaboration of mechanisms of organic acid metabolism in pear after harvested.Chromatographic separating condition of organic acid was optimized. Mobile phase was 3% methanol-0.01 mol/L K₂HPO₄(pH 2.55)solution, column temperature was 30℃using ultraviolet detector. Mobile rate was 0.5 mL/min and the detecting wavelength was 210 nm.The study on pear fruit physiological changes in different treatments showed that pullulan treatment and calcium treatment could significantly inhibit respiration, reduce titratable acid contents of pulp and peel, and delay the after-ripening and senescence of Huangguan pear in order to improve the quality of postharvest pear.The research of different treatments on malic acid, citric acid content changes showed that pullulan treatment and calcium treatment could change malic acid content changing trends, but reduce the content of citric acid. Calcium treatment on pulp had significant influence on malic acid content (p<0.05), however, two kinds of treatments had no significant influence on citric acid content.The study on three related enzymes of malic acid which were NAD-MDH, NADP-ME and PEPC shows that the activity of NAD-MDH was the highest. The correlation between malic acid content and the activity of NAD-MDH reaches significant level in different tissues (pulp and peel). The correlation between the activity of NADP-ME and malic acid content was negative and the correlation reached significant level in pulp. There is no significant relativity between the activity of PEPC and malic acid content in various treatments. The experimental results demonstrated that NAD-MDH and NADP-ME were the key enzymes which regulate the malic acid in Huangguan pear fruit after harvested. Investigation for activity variation of NAD-IDH, PEPC, CS, Mit-ACO and Cyt-ACO, five enzymes associated with citric acid metabolic process, showed that PEPC and CS had a significant impact on the variation of citric acid content in post-harvest fruit. Mit-ACO, Cyt-ACO, NAD-IDH had a negative correlation, but not significantly, with citric acid content. The experimental results demonstrated that PEPC and CS were the key enzymes in the regulation of citric acid metabolism for Huangguan pear after harvest.