茉莉酸甲酯处理对采后龙眼果皮褐变的影响

本实验以10、50、100μmol/L MeJA处理‘储良’龙眼(Dimocarpus longan Lour.)果实，研究其对(20±1)℃、85%相对湿度贮藏条件下的龙眼果皮褐变的影响。结果表明：与对照组相比，MeJA处理可有效降低‘储良’龙眼采后果皮褐变指数、果皮细胞膜透性和果肉自溶指数，而且MeJA浓度越高，抑制效果越明显。与对照组相比，100μmol/L MeJA处理龙眼果实能够保持较高的果皮总酚和类黄酮含量，降低果皮多酚氧化酶活力，有效提高果皮过氧化物酶和苯丙氨酸解氨酶活力；另一方面，MeJA处理可以有效降低超氧阴离子自由基产生速率以及H₂O₂含量，有效增强抗氧化酶(超氧化物歧化酶、过氧化氢酶)活力以及1,1-二苯基-2-三硝基苯肼自由基清除能力，提高果皮抗氧化能力。综上，100μmol/L MeJA处理可抑制龙眼果实采后部分酚类物质代谢，增强其抗氧化能力，从而延缓龙眼采后果皮褐变的发生，延长贮藏保鲜期。

Effect of Methyl Jasmonate Treatment on Postharvest Pericarp Browning of Longan Fruit

In this research, we investigated the effects of treatment with different concentrations (10, 50 and 100 μmol/L) of methyl jasmonate (MeJA) on postharvest browning of ‘Chuliang’ longan fruit (Dimocarpus longan Lour.) during storage at (20 ± 1) ℃ and 85% relative humidity. The results showed that compared with the control fruit, MeJA treatment effectively reduced pericarp browning index, pericarp cell membrane permeability and pulp breakdown index in a concentration-dependent manner. In addition, 100 μmol/L MeJA maintained higher contents of total phenols and flavonoids, reduced the activity of polyphenol oxidase (PPO), and increased the activity of peroxidase (POD) and phenylalanine ammonialyase (PAL) in the pericarp. MeJA treatment could effectively reduce the rate of superoxide anion production and H2O2 content, enhance the activity of antioxidant enzymes (superoxide dismutase (SOD) and catalase (CAT)) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging capacity, and improve antioxidant capacity. Therefore, it is concluded that 100 μmol/L MeJA treatment can inhibit postharvest phenolic metabolism and increase antioxidant capacity in longan fruit, thus delaying pericarp browning and prolonging its storage.