番荔枝贮藏过程中品质营养变化与糖代谢相关性及其调控研究

The pulp of Annona squamosa (custard apple) is exquisite, unique flavored and rich in nutrition, but easy to soften and rot after full ripeness to be soft. Hence, it is not resistant to storage, transportation and sold in distant markets. Furthermore, the edible flesh contains high content of fructose, sucrose, glucose and oligosaccharide, making it become high calorie fruit and thus restricting the industrialization development. On the basis of preliminary analysis in the changes of nutrition and sugars of Annona squamosa during storage, this project integrates sugar chemistry, molecular biology, enzymology and food science to study the correlation between fruit softening and cell wall sugar metabolism, fruit nutrition change and sugar metabolism of Annona squamosa during storage. Through the analysis of change in the gene expression amount of sugar metabolism related enzyme, the key sugar metabolism enzymes affecting fruit softening and nutrition change are screened and determined. By regulating the activity of key enzymes, the fruit of Annona squamosa has a delayed soften course, decreased content of low molecule sugar with high calorie, increased content of active polysaccharide and improved quality and nutrition, which provide theoretical basis and technical gist for quality and nutrition improvement of Annona squamosa during storage.

番荔枝果肉肉质细腻，风味独特，营养丰富，但容易软化，完熟后柔软，易腐烂变质，因此不耐贮藏和运输，难以远销，且果肉可食用时果糖、蔗糖、葡萄糖和寡糖等含量很高，为高热量水果，从而制约其产业化发展。本课题在前期初步分析了番荔枝在贮藏过程中品质营养及糖类物质变化的基础上，综合糖化学、分子生物学、酶学及食品科学等，研究番荔枝在贮藏过程中果实软化与细胞壁糖类代谢相关性、果实营养变化与糖类代谢相关性，通过分析糖代谢相关酶基因表达量的变化，筛选确定出番荔枝果实软化的糖代谢关键酶及影响番荔枝果实营养变化的糖代谢关键酶，通过对关键酶活性调控，延缓番荔枝软化，降低果实中高热量低分子糖，增加活性多糖，提高番荔枝的品质及营养，为番荔枝在贮藏期的品质营养改良提供理论基础和技术依据。

番荔枝果肉清甜爽口，风味独特，营养丰富。但采摘后容易软化，发生裂果、褐变，不耐贮藏和运输，难以远销，且果肉可食用时的果糖、蔗糖、和葡萄糖等含量很高，为高热量水果，制约了其产业化发展。本研究在前期初步分析番荔枝在贮藏过程中品质营养及糖类物质变化的基础上，综合糖化学、分子生物学、酶学及食品科学等对番荔枝在贮藏过程中果实软化及营养与糖类代谢相关性进行了探究，同时对代谢关键酶进行了筛选和调控。结果表明：番荔枝果实软化与细胞壁多糖组分，尤其是水溶性果胶（WSP）与KOH溶性半纤维（HC4）之间显著相关。随着贮藏时间的延长，番荔枝果实基因的表达量增高，与贮藏前期相比，番荔枝中期和后期分别有3168个和2897个差异表达基因，且DEGs最主要的是淀粉和蔗糖代谢通路。相关性分析结果表明，番荔枝果实硬度仅与纤维素酶（Cx）酶活、Cx基因表达量呈显著负相关，因此筛选确定出番荔枝软化过程中细胞壁糖类代谢关键酶为Cx酶。利用1-MCP、氯化钙和壳聚糖对Cx酶进行调控，发现1-MCP处理后番荔枝果实Cx基因表达量始终低于对照组，效果最佳。通过对番荔枝糖含量测定发现番荔枝为蔗糖积累性果实。通过糖代谢酶基因的相对表达量筛选确定出酸性转化酶（AI）为番荔枝糖代谢的关键酶。利用氯化钙、壳聚糖和普鲁兰多糖对番荔枝进行涂膜处理，发现氯化钙和壳聚糖的保鲜效果较好，且氯化钙处理对番荔枝采后蔗糖代谢通路的调控影响最显著。此外，我们发现利用果糖基转移酶将番荔枝汁中的蔗糖转化为活性寡糖（蔗果三糖），能够降低番荔枝蔗糖含量，提高活性寡糖含量。综上所述，本研究从番荔枝软化及品质与糖代谢的关系入手，改变了碳水化合物的代谢和分配，为延长番荔枝软化开辟了新途径，为番荔枝在贮藏期的品质改良奠定了基础。