采后荔枝果皮褐变过程中的生理变化研究

[目的]荔枝采后果皮褐变严重降低了果实的商品价值,限制了荔枝贸易的发展.本文通过研究采后荔枝果皮褐变过程中的生理变化,寻找影响果皮褐变的主要因素,为阐释果皮褐变机理提供基础. [方法]妃子笑果实贮存于温度25℃.相对湿度70%±5%条件下,每8 h测定一次果实形态及生理变化. [结果]妃子笑荔枝采后72 h内完全褐变,其中,在采后48-64 h褐变指数急剧上升,好果率急剧下降.随褐变程度的增加,果实与果皮失水量增加,但果肉含水量变化不大.果皮丙二醛含量、pH值和相对电导率都随褐变加重而增加,而花色素苷、类黄酮、总酚、叶绿素a和总叶绿素含量则下降.果皮POD活性在采后32 h上升,然后下降,而PPO活性一直下降.过氧化氢酶和超氧化物歧化酶活性都呈现先升后降然后再升高的趋势.相关分析,逐步回归分析和通径分析表明,果皮失水是引起果皮褐变的主要原因.主成分聚类分析表明果皮褐变町分为两个阶段. [结论]果皮水分状况是影响果皮褐变的主要因素.果皮褐变过程呈现阶段性变化,主要由果皮失水决定. Abstract： [Objective] Pericarp browning in the postharvest litchi significantly reduced its commercial value and limited the expanding of litchi markets.Physiological changes during the process of pericarp browning were determined in order to identify the underlying mechanisms,[Method]Matured Feizixiao fruits were stored at 25 ℃ and 70%±5% relative humidity.The physiological changes happened in pericarp during storage were tested at an 8-hour interval. [Result] The fruit of Feizixiao (Litchi chinensis Sonn.cv Feizixiao) turned completely brown within 72 h after being harvested under the experimental conditions.Sharp increase of the browning index occurred from 48 to 64 hours after harvest (HAH).With the browning of pericarp,water content of the whole fruit and pericarp decreased continuingly.In contrast,there were no significant changes in the water content of pulp during the same period.MDA content,pH value and relative leakage rate of pericarp were increased during storage.Most of pigment contents including anthocyanin,flavonoid,phenols,chlorophyll a and total chlorophyll decreased.POD activity was initially increased in 32 HAH and then decreased afterwards.PPO activity was decreased continuously,while the activities of catalase and superoxide dismutase exhibited the pattern of "increasing-decreasing-increasing" as the storage time progressed.Correlation,stepwise regression and path analyses showed that water loss of pericarp was the major factor of pericarp browning.Principal and cluster analyses showed that there were two stages of pericarp browning during the course of litchi storage. [Conclusion] Water status of pericarp was the most important factor affecting pericarp browning.The pericarp browning happened by stages,which was mainly determined by the water loss of pericarp.