【作者】 林瑜；

【导师】 林河通；

【作者基本信息】 福建农林大学 ， 食品科学， 2008， 硕士

【摘要】 龙眼（Dimocarpus longan Lour.）是我国南方主要的亚热带果树之一,果实营养价值丰富,具有很高的药用价值和保健价值。近十年来,我省龙眼生产发展迅速,产量逐年增加。但果实成熟于高温季节,采后极易褐变、果肉自溶和果实腐烂而使果实迅速劣变,货架期很短,常温下只有一周的采后寿命,这种短的采后寿命严格限制龙眼的贮运、销售和消费。果肉自溶是采后龙眼败坏的主要原因之一,严重影响其食用品质和商品价值,是限制龙眼果实长期贮运的关键因素之一。但有关龙眼果肉自溶与生理衰败和微生物病害的关系的研究报道甚少。龙眼果实生长期间普遍受到焦腐病菌[Lasiodiplodia theobromae（Pat.）Griff.& Maubl]等病原菌的潜伏侵染,焦腐病是龙眼果实采后的主要病害,引起龙眼果肉自溶等症状。本研究以果实采前套袋控制病原菌潜伏侵染的“立冬本”龙眼果实为材料,果实采后接入焦腐病菌,在（25±0.5）℃下保湿培养,从活性氧和细胞壁代谢两方面着手,研究焦腐病菌侵染引起龙眼采后果肉自溶的机理。研究结果如下:1.与没接菌的对照龙眼果实相比,接入焦腐病菌的龙眼果实采后果肉自溶速率明显加快,症状严重,果肉自溶指数极显著（P＜0.01）高于对照龙眼果实。2.接入焦腐病菌的龙眼果肉活性氧代谢与对照龙眼果肉有着明显的差异。采后5 d,接入焦腐病菌的龙眼果肉O₂^-.产生速率急速上升而后期略有下降,SOD活性呈上升趋势,CAT活性呈迅速下降的趋势,APX活性则呈现先增加而后急速下降的趋势,LOX活性呈快速上升的趋势,膜脂过氧化产物MDA和内源抗氧化物质AsA、GSH含量都大致呈现先增加后减少的趋势;而对照龙眼果肉无明显变化。上述结果表明,贮藏前期为相对静态感染期,果肉中O₂^-.产生速率变化不大,其增加有利于抑制病菌孢子萌发和菌丝生长,果肉可通过自身的代谢调节以抵御病原菌的入侵,AsA、GSH含量提高,有利于清除果肉的自由基,使果肉活性氧代谢维持动态平衡,并延缓了膜脂过氧化作用;但在贮藏中后期,焦腐病菌的侵染对活性氧清除酶系统产生了破坏作用,果肉中自由基清除酶的活性变化紊乱,AsA、GSH被快速消耗,自由基大量积累,MDA含量显著增加,膜系统被破坏,膜透性增加加快,加剧了果肉自溶的进程。这说明焦腐病菌的侵染加速了龙眼果肉膜脂过氧化作用的进程,病原菌侵入是导致龙眼氧化还原代谢失调,引发果肉自溶的重要原因。3.接入焦腐病菌的龙眼果肉细胞壁组分代谢及其细胞壁降解酶活性的变化与对照龙眼果肉有着明显的差异。采后5 d,接入焦腐病菌的龙眼果肉细胞壁组分（果胶、纤维素、半纤维素,细胞壁蛋白等）代谢基本呈现先增加后急速下降的趋势;而对照龙眼果肉无显著变化。接种的果肉细胞壁降解酶（PE、PG、纤维素酶、β-半乳糖苷酶等）在贮藏前期均呈不断上升的趋势,其活性上升速率显著高于对照龙眼。从而说明,在贮藏前期,焦腐病菌入侵后,龙眼果肉发生细胞壁增厚和木质化现象,龙眼果肉内含纤维素、半纤维素含量增高,从而使得果肉细胞壁增厚,抵御了微生物的攻击;而在贮藏中后期,随着果实的代谢和衰老,病原菌菌丝体大量繁殖,激发了相关酶的活性,使细胞壁降解酶活性迅速升高,同时龙眼果肉的细胞组织结构遭到破坏,使细胞壁组分物质与酶充分接触而加速降解,最终导致果肉汁液外流,腐败酸臭,加速了果肉自溶衰老的进程。更多还原

【Abstract】 Longan （Dimocarpus longan Lour.） is a famous subtropical fruit species in the South of China. It’s rich in nutritional value, medicinal value and health value. Since longan fruit mature during the hot and humid August/September in China, the fruit deteriorate rapidly after harvest due to pericarp browning, aril breakdown and decay, the fruit have a very short postharvest life of a week at ambient temperature. This short postharvest period limits its long-distance transportation, marketing and consumption. One of the main reasons that the longan fruit deteriorate rapidly is aril breakdown. Aril breakdown seriously affect the eating quality and commodity value. The study of the relationship between aril breakdown and post-harvest disease are rarely reported. The dominant factor lead to aril breakdown of postharvest longan fruit has not yet verdicted.The black-rotten disease caused by Lasiodiplodia theobromae （Pat.） Griff. &Maubl is the main disease of postharvest longan fruit in Fujian Province of China. The materials of this experiment were fruits of longan （Dimocarpus longan Lour. cv. Lidongben）, which were inoculated with Lasiodiplodia theobromae （Pat.）Griff. &Maubl. In this experiment, we researched the changes of active oxygen species and cell wall metabolism in aril of longan inoculated with Lasiodiplodia theobromae （Pat.） Griff. &Maubl.. The possible mechanism on aril breakdown of postharvest longan fruit after pathogen infection was also hypothesized. The results were as follows:1. Aril breakdown of longan fruit after inoculation with Lasiodiplodia theobromae （Pat.）Griff. &Maubl. was extremely serious compared with the controlled longan. Aril breakdown rate accelerated obviously and aril breakdown index was remarkable higher （P<0.01） than the controlled longan.2. The changes of active oxygen species metabolism in aril of longan inoculated with Lasiodiplodia theobromae （Pat.） Griff. &Maubl. are remarkable different from the controlled longan. After inoculation with Lasiodiplodia theobromae （Pat.） Griff. &Maubl., productive rate of O₂^-· increased at first and then decreased, SOD and LOX activity enhanced sharply, CAT activity decreased gradually, APX activity and contents of endogenous antioxidant substances （AsA, GSH） increased at first and then decreased gradually during storage, however, these phenomena didn’t happened at the controlled longan. From the results it can be seen that pathogen infection destroyed the system of reactive-oxygen-scavenging enzymes. AsA、GSH were consumed quickly, the content of hydrogen peroxide increased, productive rate of superoxide radical anion enhanced., membrane systems were damaged and membrane permeability increased. So the progress of aril breakdown was accelerated. It shows that pathogen infection is the dominant factor that lead to aril breakdown of postharvest longan fruit.3. The changes of cell wall metabolism and the activities of their hydrolases in aril of longan inoculated with Lasiodiplodia theobromae （Pat.） Griff. &Maubl. are remarkable different from the controlled longan. The content of cell wall components in longan after inoculation with Lasiodiplodia theobromae Pat. increased at first and then decreased gradually during storage, however, these phenomena didn’t happened at the controlled longan. The activities of hydrolases in longan after inoculation with Lasiodiplodia theobromae Pat. increased continuously during the early storage, and its increased rate was significantly higher than the controlled longan. From the results it can be seen that pathogen infection stimulates the activity of hydrolases. So the structure of longan fruit was damaged and the cell wall components deteriorate fast. Ultimately it lead to the flesh juice outflows until corruption, and accelerate the progress of aril breakdown.更多还原