新型柑橘源RG-I型果胶精细结构及其凝胶分子机制研究

RG-I enriched pectin exists extensively in the wastes of processed fruits and vegetables with active probiotic functions for gut microbiota; however, their poor gelling property limits their application in food industry as hydrocolloids and was removed by the hot acid treatment during the commercial pectin production. References and our previous results showed that such polysaccharides could form gel under sugar free system with pH and microwave induction, however, its mechanism still awaits further investigation. Hence, the present study will prepare a novel RG-I enriched pectin from citrus with the mild temperature extraction, which had been set up by the cooperation with the company. The detailed structure of the pectin will be determined with selective enzymatic hydrolysis and NMR assisted HILIC-MS-MS to reconstruct different structural domains of the pectin, using a strategy of top-down. Furthermore, the mechanism and the model of gelling will be demonstrated by investigating the hydrogen bonding, ion effect and the structure of the side chains of the pectin, using results of rheology, texture and micro-analysis (fluorescence labelling and Cryo-EM). The effects of the RG-I enriched pectin on gut microbiota will also be investigated to further improve its value for application. The present study will not only provide theoretical basis for the technical transformation of traditional pectin manufacturing and the development of novel RG-I enriched pectin, but also provide new sight for the comprehensive application of pectin from the wastes of processed fruits and vegetables.

鼠李半乳糖醛酸聚糖I（RG-I）型果胶在果蔬加工废弃物中大量存在且具有优越的肠道益生等活性，但因其凝胶性能差而在传统果胶制备中被去除，也没有在食品工业中作为胶体应用。文献及本课题组前期研究表明此多糖可在pH和微波诱导等体系中形成无糖凝胶，但成胶分子机制不明确。因此，本研究将采用课题组建立的“低温融合技术”制备柑橘源RG-I型果胶，通过定向酶解、NMR辅助HILIC-MS-MS等技术鉴定果胶不同结构域的精细结构和排列方式，提出其全结构的分子模型；在此基础上，通过流变学、质构和微观学分析（荧光标记和低温冷冻电镜）等手段，从氢键、离子效应和侧链精细结构等角度探讨其凝胶形成机制，构建凝胶模型；通过对该新型果胶肠道益生功能的评价，提升其作为保健型食品胶体的应用价值。本研究结果将为改变传统果胶生产工艺，开发具有益生元功能的新型RG-I果胶奠定理论基础，更为全面利用果蔬加工废弃物中的果胶提供新思路。

鼠李半乳糖醛酸聚糖I（RG-I）型果胶在果蔬加工废弃物中大量存在且具有优越的肠道益生等活性，可在pH和微波诱导等体系中形成无糖凝胶，但成胶分子机制不明确。本项目以柑橘为原料，建立了RG-I果胶靶向提取技术，得到柑橘源RG-I果胶，并通过氧化降解、NMR辅助HILIC-MS-MS等技术鉴定了其精细结构和排列方式，为RG-I果胶工业化制备和糖类化合物精细结构分析提供了新的方法和技术；利用流变学、质构和微观学分析等手段，探讨了氢键、离子效应和侧链精细结构对RG-I果胶凝胶形成影响规律，并阐明了其凝胶机理；利用不同结构果胶开展了肠道益生功能的评价，分析了其对高糖高脂诱导糖脂代谢和肠道菌紊乱的影响，阐述了不同结构果胶肠道益生活性及机制的差异，为RG-I果胶作为保健型食品胶体的应用提供了理论参考。结果发现，RG-I果胶在阳离子诱导的低酯RG-I型果胶凝胶中，二价阳离子与HG结构域通过离子相互作用形成蛋盒结构，RG-I侧链可通过链缠结增强钙凝胶的“蛋盒结构”；对于酸诱导凝胶，低pH值会促进果胶链间氢键和疏水相互作用形成凝胶网络，中性糖侧链通过氢键作用加强凝胶网络结构；RG-I果胶较低分子量RG-I果胶和富含HG结构域果胶具有更显著的肥胖抑制效果，能有效缓解肥胖小鼠血脂异常现象、改善血糖代谢紊乱，也能逆转肠道菌群紊乱，提高肠道菌群的多样性和丰富度，促进白色脂肪棕色化。本项目成果在JAFC, Carbohyd. Polym，Food Chen等国际一流刊物上发表论文18篇。这些成果将为改变传统果胶生产工艺，开发具有益生元功能的新型RG-I果胶奠定理论基础，更为全面利用果蔬加工废弃物中的果胶提供新思路。