采后苯并噻重氮处理对‘玉金香’甜瓜氨基酸代谢酯类香气物质及其代谢机理的影响

以‘玉金香’甜瓜为材料,采后常温贮藏期间分析其氨基酸含量、谷丙转氨酶(glutamate pyruvic transaminase,GPT)、谷草转氨酶(glutamic oxaloacetic transaminase,GOT)、丙酮酸脱羧酶(pyruvate decarboxylase,PDC)、丙酮酸脱氢酶(pyruvate dehydrogenase,PDH)活力及其代谢产物酯类香气物质含量的变化,探讨采后苯并噻重氮(benzothiadiazole,BTH)诱抗处理对酯类香气物质氨基酸代谢途径影响的机理。结果表明:BTH诱抗处理可延迟样品酯类香气物质释放高峰出现,抑制其释放,总含量比CK组(未经任何处理)低19.10%。15种游离氨基酸被分离确定,CK组氨基酸总含量峰值(14 597μg/g)出现在第6天,BTH组峰值出现在第8天,低于CK组9.47%(P0.05)。BTH处理抑制了贮藏期间GOT、PDC和PDH活力,与CK组相比,BTH处理组果皮GOT、PDC和PDH活力峰值分别降低31.80%、16.86%和24.30%,果肉峰值分别降低19.10%、14.70%和25.56%,果皮GOT活力被显著抑制(P0.05);不同处理组间GPT活力差异不显著(P0.05)。氨基酸总含量、GOT活力与酯类香气物质含量呈极显著正相关(P0.01)。水处理对氨基酸含量、代谢酶活力及其产物酯类香气物质释放均有影响,但无明显作用规律。由此可见,BTH处理会减少氨基酸含量,抑制相关代谢酶活力,进而改变其产物酯类香气物质的释放。

Effect of Postharvest Benzothiadiazole Treatment on Aroma Esters Derived from Amino Acid Metabolism and Metabolic Mechanism in ‘Yujinxiang’ Melon

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.