伯谢克辛甜瓜果肉迅速软化机理研究

Xinjiang is the largest high-quality muskmelon (Cucumis melon L.) origin, planting area in the world that provides rich germplasm resources for multi-angle development and utilization. Boxiekexin is special and extreme in melon variety with the character of soft, juicy, sweet and fragrant. There should be a softening digestion system inside. Nature may provide us with a rare, efficient enzyme technology from perspective of juice processing. Therefore, it will be helpful to scientific utilization and development of melon juice making technology if we know the mechanism inside. In the fruther work, Xinjiang Boxiekexin melon and 86-1 melon are used as experiment materials. The underling biochemical mechanisms for fruit softening will be carried out. The changes of pulp ultrastructural, endogenous ethylene, and enzyme activity of cell wall degradation as well as its gene expression will be determined. The changes in correlation and the internal function for softening will be analyzed. The rapid softening enzyme system for Boxiekexin melon and its regulation mechanism will be constructed. This work will help to understand the endogenous mechanism of melon for fast fruit softening after postharvest; it will enhance the knowledge of fruit ripening; it will also provide basis for the development of new technologies for processing melon juice and improvement the efficiency for production and product quality.

新疆我国优质甜瓜原产地和主产区，为多角度开发利用提供了丰富的种质资源。伯谢克辛甜瓜突出特点是采后瓜肉迅速软化、液化，在甜瓜中极为特殊和极端，应该存在着高效运行的软化酶解体系。从制汁角度看，也许是自然界提供的一套高效酶解技术方案，认识其运行机制将有助于科学利用和促进甜瓜制汁技术的创新发展。项目以伯谢克辛甜瓜为材料，86-1甜瓜为对照，测定伯谢克辛和86-1成熟软化过程中瓜肉超微结构、内源乙烯和细胞壁物质变化，细胞壁降解酶及其基因表达水平的变化，分析这些变化发生相关性及对软化内在调控作用，给合对照86-1甜瓜的变化差异，构建伯谢克辛甜瓜采后迅速软化酶解体系及调控机制。研究有助于增加对甜瓜采后软化的深刻认识，也为甜瓜制汁技术创新、科学制订甜瓜汁工艺、有效调控其软化进程、实现高效、高品质甜瓜汁生产提供知识基础和科学依据。

研究了伯谢克辛甜瓜（溶质果肉）和86-1甜瓜（不溶质果肉）成熟软化过程中果肉超微结构、乙烯和细胞壁物质的变化规律，比较了细胞壁降解酶活性及基因表达规律，了解伯谢克辛甜瓜果肉迅速软化的调控机制，优化伯谢克辛甜瓜内源酶酶解制汁的方案。‘伯谢克辛’甜瓜果实软化程度、呼吸强度显著高于‘86-1’甜瓜，采后呼吸作用在果实软化过程中发挥了重要的作用。‘伯谢克辛’甜瓜细胞壁中可溶性果胶含量高于‘86-1’甜瓜，‘伯谢克辛’甜瓜后熟软化过程中PG、β-G、Cx、PME起到了关键作用。不同浓度的乙烯利（500mg/L、300mg/L）和1-MCP（2μL/L、1μL/L）可调控‘伯谢克辛’甜瓜果实软化速率。1-MCP能有效延缓伯谢克辛甜瓜的软化进程，较好的保持果实硬度，降低了甜瓜果实呼吸高峰，抑制细胞壁降解酶活性和果胶物质的降解；乙烯处理细胞壁降解酶活性提高，果胶物质发生明显的降解，果实快速软化。采前、采后伯谢克辛甜瓜的果实硬度始终小于86-1甜瓜，呼吸和乙烯生成量大于86-1甜瓜。两种甜瓜采前、采后细胞由小到大呈持续生长。86-1甜瓜细胞结构紧密且细胞器完整，而伯谢克辛甜瓜在采前细胞结构开始逐渐松散，细胞器由多变少，细胞壁及细胞膜变化明显。伯谢克辛甜瓜检出香气成分26种，呈果香型；86-1甜瓜检出香气成分9种，呈花香型。甜瓜转录组测序，对功能基因进行注释，分析出多个细胞壁降解酶基因，包括：多聚半乳糖醛酸酶、果胶甲酯酶、纤维素酶、β-葡萄糖苷酶活性。KEGG Pathway富集分析，筛选X08R-VS-B08R主要涉及的通路有13条，与甜瓜果实衰老软化功能紧密相关。克隆了‘伯谢克辛’甜瓜果肉细胞壁降解酶（CB/CX/PME/PG）相关基因9个。甜瓜在采前、采后的不同时期CmPG1、CmPG2、CmPG8、CmPME3、CmPME4、CmCX2、CmCB1、CmCB2、CmCB4相对表达量表现出不同规律，与果实的成熟、软化、衰老密切相关。伯谢克辛甜瓜可作为甜瓜汁加工的原料。最优酶解条件为乙烯利浓度510mg/L、酶解时间2.25h、酶解温度20℃，伯谢克辛甜瓜出汁率为85.239%。研究增加了对溶质果肉甜瓜软化规律的认识，为甜瓜采后软化进程的调控，改善果实品质提供研究基础和科学依据。