Abstract: Muskmelon (Cucumis melo L. cv. Yujinxiang ) was analyzed for changes in the contents of amino acids and aroma esters derived from amino acid metabolism and the activities of glutamate pyruvic transaminase (GPT), glutamic oxaloacetic transaminase (GOT), pyruvate decarboxylase (PDC) and pyruvate dehydrogenase (PDH) during postharvest storage at room temperature. This study examined the influence of postharvest benzothiadiazole (BTH) treatment on the amino acid mechanic pathways for the production of aroma esters, and it also elucidated the underlying mechanism. The results showed that the peak time of aroma esters was delayed and the release amount was inhibited by 19.10% by BTH treatment as compared to the untreated control. A total of 15 free amino acids were separated and identified; total free amino acid content in the control group reached its peak (14 597 μg/g) on the 6th day of storage, whereas the peak for the BTH treatment group appeared on the 8th day, 9.47% lower than that of the control (P < 0.05). BTH treatment inhibited the activities of GOT, PDC and PDH during storage and reduced these enzyme activities by 31.80%, 16.86% and 24.30% for peel and by 19.10%, 14.70% and 25.56% for pulp, respectively and it significantly inhibited GOT activity in peel (P < 0.05). On the other hand, no significant difference in GPT activity existed between the groups (P > 0.05). Total amino acid content and GOT activity were highly significantly positively correlated with the content of aroma esters (P < 0.01). Water treatment affected amino acid contents, metabolic enzyme activities and the release of aroma esters as metabolites, but this effect was irregular. Therefore, BTH treatment can reduce amino acid contents, and inhibit the activities of related metabolic enzymes, thereby affecting the release of aroma esters.

Key words: benzothiadiazole, aroma ester, amino acids, transaminase, pyruvate decarboxylase, pyruvate dehydrogenase