PRO-LONG涂膜对采后贮藏荔枝果实色泽和酶活性变化的影响

EFFECTS OF PRO-LONG COATING ON CHANGES IN COLOUR AND ENZYME ACTIVITY OF POSTHARVEST LITCHI FRUIT

本文以荔枝品种“槐枝”为材料，以1．5％和2．5％Pro-long涂膜处理果实，研究Pro-long涂膜对果后贮于4℃的荔枝果皮色泽变化和有关酶活性的变化。对照和处理的HunterL值和b值均随贮藏时间的延长而降低，处理的比对照的下降慢。采后贮藏开始21d内，对照和处理的HuntCra值变化很小，保持相对稳定，之后的贮藏时间内有较显著的下降，说明贮藏初期果实的红色特性变化较少，之后变化很明显，这与果皮花色素苷、类黄酮、总酚的变化是相对应的。在贮藏后期，处理的HuntCra值下降明显较对照慢。Hunter值的变化与在贮藏过程中果实外观逐渐变成暗红和揭变以及在果实的来后根变中起着重要作用的多酚氧化酶和部分地涉及褐变过程的过氧化物酶的变化相对应。处理的过氧化物酶活性增加较对照慢，而且，与对照比较，多酚氧化酶的峰值稍稍延迟了。未发现l‘5％和2．5％处理间有明显差别。因此，Pro-long涂胶对荔枝的应用可以部分地降低多酚氧化酶和过氧化物酶，影响果皮花色素苷的降解、类黄酮和总酚的变化，延迟了褐变过程的发生。

A common litchi cultivar Huaizhi was used to investigate how the application of Pro-long coating affects the browning of litchi peel and relevant enzymes during 4 t storage. The Hunter L and b values in both the control and treated fruits decreased continuously with storage time, indicating that the peel became darker and had less yellow characteristics. The Hunter L and b values in the control decreased faster than those in treated fruits. The Hunter a values ifl both the control and treated fruits were relatively stable during the first 20 days of storage and then significantly decreased during the remaining days, implying that stored litchi fruits maintained basically red characteristics during the first 20 days of storage and then became less red, corresponding to the changes in contents of anthocyanin, flavonoid and total phenolics. Hunter a values in the control decreased faster than those in treated fruits after the 21st day of storage. These correspond to a visible change to a dark red and brown during storage and changes in polyphenol oxidase (PPO) and peroxidase (POD), which indicate that polyphenol oxidase plays a definitive role in postharvest browning, and peroxidase is partially involved in the browning process. The increase in POD activities of treated fruits was slower than that of the control, and the peaks in PPO activities of treated fruits were delayed slightly compared to that of the control. There was no significant difference between 1.5% and 2.5% Pro-long treatments. Therefore, we suggest that the application of Pro-long coating to litchi fruits partially inhibits PPO and POD activities, and influences the breakdown of anthocyanin and the changes in contents of flavonoid and total phenolics, thereby delaying browning progress.