在常温货架期间冷藏荔枝的褐变机理

Pericarp browning is a key problem of affecting postharvest litchi fruit quality during storage and transportantion. Low temperature is a most efficient approach to controll pericard browning of harvested litchi fruit,but the cold-stored litchi fruit are highly perishable with a very short postharvest life during shelf time at ambient temperature. Currently, there are many studies focused on browning mechanism from downstream of litchi pericard enzymatic browning at home and abroad, but there is little study on inducement of ezymatic browning.This research project is to elucidate pericard browning mechanism of cold-stored litchi fruit during shelf time at ambient temperature, based on investigating the role of membrane lipid and energy metabolism in membrane structure and fuction regulation and cold-stored litchi fruit peel browning from the standpoint of biomembrane deterioration. The main research contents are as follows: 1) effects of phospholipid and unsaturated fatty acid metabolism of litchi fruit on membrane integrity and function during cold storage and shelf time at ambient temperature; 2) effects of energy metabolism of litchi fruit on membrane integrity and function during cold storage and shelf time at ambient temperature. 3) To clarify the role of membrane lipid and energy metabolism of cold-stored litchi fruit in membrane deterioration and pericard browning through investigating changes in characteristic property of membrane lipid and energy metabolism, and membrane structure and function on condition that litchi fruit consenescence is controlled by manpower. Research results of this project is to better understand mechanism of cold-stored litchi browning in theory and provide a new idea for further developing a technology to controlling cold-stored litchi fruit peel browning in practice.

荔枝果实采后褐变是影响贮运保鲜主要问题。低温是控制荔枝果皮褐变的最有效手段，但冷藏荔枝果实在常温货架期间极易发生褐变，严重影响贮运保鲜。当前，国内外主要从酶促褐变的下游开展荔枝果皮褐变机理的研究，对引起酶促褐变的诱因研究很少。本项目拟从膜劣变角度入手，研究膜脂代谢、能量代谢在膜结构和功能调节以及荔枝货架期果皮褐变中的作用，从衰老的原初过程及其作用方式阐明货架期果皮褐变的机理。主要研究：1）荔枝在冷藏和货架期间，磷脂代谢和不饱和脂肪酸代谢对膜完整性和功能的影响；2）荔枝在冷藏和货架期间，能量代谢对膜完整性和功能的影响；3）人工调控果实组织衰老条件下，通过研究果皮膜脂和能量代谢特性、膜结构和功能的变化，以揭示膜脂和能量代谢在膜劣变和果皮褐变中的作用。本项目研究成果在理论上可丰富荔枝果皮褐变的发生发展机制；在实践上，为进一步探讨适当的减缓果实褐变的技术提供新思路。

荔枝果实采后褐变是影响贮运保鲜主要问题，低温是最有效的控制手段，但冷藏荔枝果实在常温货架期间极易发生褐变，严重影响贮运保鲜。当前，国内外主要从酶促褐变的下游开展荔枝果皮褐变机理的研究，对引起酶促褐变的诱因研究很少。. 本项目从膜劣变和能量代谢角度入手，主要研究了：（1）荔枝在冷藏和货架期间，磷脂代谢和不饱和脂肪酸代谢对膜完整性和功能的影响；（2）荔枝在冷藏和货架期间，能量代谢对膜完整性和功能的影响；（3）ATP、DNP 、厌氧和正丁醇处理对冷藏荔枝果实在常温货架果皮褐变，膜脂和能量代谢特性、膜结构和功能的影响。. 主要研究结果如下：（1）冷藏时间延长加快了荔枝果实中磷脂酰胆碱(PC)和磷脂酰肌醇（PI）含量在货架期下降和磷脂酸（PA）含量增多，磷脂降解加快。同时，膜脂的DBI和膜的流动性也明显下降，从而增加了膜的不稳定性和通透性。正丁醇处理显著抑制了冷藏荔枝果实的褐变和霉变，抑制了细胞膜磷脂降解，提高膜流动性，保持了较为完整的细胞结构。(2) 冷藏荔枝果实在货架期果皮组织能量状况明显受低温贮藏时间和常温货架期的影响。冷藏时间延长加快果实组织能量亏损，并伴随果实严重褐变。 (3)外源ATP处理提高冷藏荔枝果实线粒体细胞色素主路活性和呼吸速率，保持较高的ATP含量和能荷水平，同时诱导了交替途径活性，减少活性氧产生及其对细胞膜伤害，从而延缓了果皮的快速褐变。DNP处理明显抑制细胞色素主路活性，抑制荔枝果皮ATP合成，导致能量亏损，促进了自由脂肪酸释放和膜结构破坏，加快果皮褐变，进一步证实了使膜结构稳定的ATP阈值的存在。（4）在冷藏荔枝果实的劣变过程中，ω-3去饱和酶基因表达减弱，而PLD与PLC基因表达增强。低温虽然诱导了ACC基因表达增强，但货架后期其表达量快速下降。SnRK表达与环境温度变化关系不大。ATP处理增强了ω-3去饱和酶基因及减少了PLC与PLD的表达。. 本项目研究成果在理论上可丰富荔枝果皮褐变的发生发展机制；在实践上，为进一步探讨适当的减缓果实褐变的技术提供新思路。