‘东壁’和‘福眼’龙眼果实果皮褐变差异的生理机制

摘要

Theharvested fruits of longan (Dimocarpus longana Lour.) are susceptible to pericarp browning, the most important factor affecting the quality and shelf-life of harvested longan fruit. The difference in postharvest pericarp browning between the longan cultivars ‘Dongbi’ (Dimocarpus longanLour.cv.Dongbi) and ‘Fuyan’ (Dimocarpus longanLour. cv. Fuyan) during storage at (8 ± 1)℃ and 85% relative humidity in relation to the metabolisms of active oxygen and phenolics were investigated. The results showed that compared to ‘Fuyan’ longans, the browning index, superoxide anion (O2-·) production rate, malondialdehyde content, and cellular membrane permeability were lower whereas the activities of active oxygen scavenging enzymes, including superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX), were signiifcantly higher and the contents of endogenous antioxidant substances, like ascorbic acid (AsA) and glutathione (GSH), were higher in the pericarp of ‘Dongbi’ longans during storage. In addition, lower activities of polyphenol oxidase (PPO) and peroxidase (POD), and higher contents of anthocyanin, lfavonoid and total phenolics in pericarp of ‘Dongbi’ longans during storage were observed as compared to ‘Fuyan’ longans. From the above results, it could be concluded that ‘Dongbi’ longans tend to be less susceptible to postharvest pericarp browning, which was due to higher active oxygen scavenging capacity, resulting in reduced accumulation of O2-·, alleviated cellular membrane lipid peroxidation, maintained structural integrity of the cellular membrane, and prevention of PPO and POD from contacting their phenolic substrates, and thus, reducing the occurrence of enzymatic browning in the pericarp of ‘Dongbi’ fruit.%比较研究在温度（8±1）℃、相对湿度85%贮藏条件下‘东壁’和‘福眼’龙眼果实的果皮褐变差异及其与活性氧及酚类物质代谢的关系。结果表明：贮藏期间，‘东壁’龙眼果实的果皮褐变指数、果皮O2－·产生速率、丙二醛含量、细胞膜透性都显著低于‘福眼’龙眼，而活性氧清除酶（超氧化物歧化酶（SOD）、过氧化氢酶（CAT）、抗坏血酸氧化酶（APX））活性和内源抗氧化物质（还原型抗坏血酸（AsA）、还原型谷胱甘肽（GSH））含量都显著高于‘福眼’龙眼；‘东壁’龙眼果实的果皮多酚氧化酶（PPO）和过氧化物酶（POD）活性都低于‘福眼’龙眼，而果皮花色素苷、类黄酮和总酚含量则高于‘福眼’龙眼。因此，采后‘东壁’龙眼果实较不容易发生果皮褐变，与其具有较强的活性氧清除能力，能减少O2－·积累，减轻膜脂过氧化作用，较好地保持龙眼果皮细胞膜结构的完整性，延缓PPO、POD与酚类物质接触而减少酚类物质的酶促氧化褐变有关。