Effects of phomopsis longanae chi infection on browning and active oxygen metabolism in pericarp of harvested longan fruits | 拟茎点霉侵染对龙眼果实采后果皮褐变和活性氧代谢的影响

صينى. 目的研究拟茎点霉侵染对龙眼果实采后果皮褐变和活性氧代谢的影响。方法采后龙眼果实用拟茎点霉孢子悬浮液（浓度为104个孢子/mL）浸泡接种5 min，以无菌水处理的龙眼果实为对照。经过处理的果实在(28?1)℃、相对湿度90%下贮藏，贮藏期间定期测定果实病害指数、果皮褐变指数、MDA含量、 产生速率、活性氧清除酶（SOD、CAT、APX）活性和内源抗氧化物质（AsA、GSH）含量的变化。结果与对照果实相比，拟茎点霉侵染提高了龙眼果实病害指数和果皮褐变指数。同时，拟茎点霉侵染促进龙眼果皮 产生速率增加，且在整个侵染过程维持较高水平；拟茎点霉侵染0―2 d内的果皮GSH含量和APX活性明显下降而SOD和CAT活性快速上升，侵染2―5 d内的果皮APX活性快速上升而SOD和CAT活性快速下降，侵染5 d后的果皮SOD和APX活性快速下降；在整个侵染过程的果皮AsA含量快速下降，而MDA含量增加。结论拟茎点霉侵染导致龙眼果皮活性氧清除能力下降而积累大量活性氧，大量的活性氧对细胞膜结构的破坏会引起细胞区室化功能的丧失，使多酚氧化酶与酚类物质接触，其结果引起酚类物质的酶促氧化和黑褐色高聚物的形成而导致龙眼果皮褐变。

إنجليزي. Objective The effects of Phomopsis longanae Chi infection on browning and active oxygen metabolism in pericarp of harvested longan fruits were investigated in this paper. Method The harvested longan fruits were inoculated with Phomopsis longanae Chi for 5 min (the concentration was 104 spores per milliliter), while the control fruits were dipped in sterile water. The treated fruits were stored at (28?1)℃ and 90% relative humidity. During fruit storage, fruit disease index, pericarp browning index, malondialdehyde (MDA) content, production rate, activities of active oxygen scavenging enzymes such as superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX), contents of endogenous antioxidant substances such as ascorbic acid (AsA) and glutathione (GSH) were determined. Result As compared to the control fruits there were higher fruit disease index and pericarp browning index of harvested longans infected with Phomopsis longanae Chi. The longan fruits infected with Phomopsis longanae Chi resulted in an increase of production rate and kept higher production rate in pericarp during the whole infection. There were obvious decreases of GSH content and APX activity, whereas, there were sharp increases of activities of SOD and CAT in pericarp of longans during infection from day 0 to day 2. During infection from day 2 to day 5, APX activity of pericarp rapidly increased, while the activities of SOD and CAT declined rapidly. After infection for 5 days, the rapid decreases of activities of SOD and APX in pericarp were observed. The amount of AsA in pericarp significantly decreased while MDA content increased during the whole infection. Conclusion The results suggest that Phomopsis longanae Chi-induced browning of longan pericarp may be due to a decrease of active-oxygen-scavenging capacity and accumulating large amounts of reactive oxygen species, which may destroy cellular membrane structure, in turn, may cause cellular de-compartmentation, resulted in polyphenol oxidase (PPO) to come into contact with phenolic substrates and oxidation phenolics to form brown polymers.