魔芋葡甘聚糖经肠道菌发酵产生氢气及短链脂肪酸的构效关系

It is obtained breakthrough in research on selective oxidation of hydrogen and its influence on other physiology function in recent years. Endogenous hydrogen mainly derives from dietary fiber intake and being fermented by intestinal flora. However, this is far from adequate research that the path of hydrogen's production and elimination is complicated in vivo. Short chain fatty acids are another set of important products of the intestinal microflora fermentation. But the physiological activity of the coexistence of the two fermentation products were not investigated. The target of this study is to explore action mechanism of dietary fiber impacting human health and provide foundation of KGM based food ingredient development and science evaluation through new angle of hydrogen and short chain fatty acid generation and selective oxidation, using intestinal microorganism as medium. Products of different molecular weight and deacetylation degree are to be prepared and characterized. In vitro anaerobic fermentation system, the dynamic effect of former specimen on bacteria community structures and metabolic products (hydrogen，short chain fatty acid etc.) is to be compared; scavenging capacity of fermentation liquid to oOH and ONOO-, as well as its capacity of selective oxidation and its cytotoxicity and genotoxicity of Caco-2 cell are to be compared. These are to illustrate structure activity relationship of KGM to intestinal bacterial phase, hydrogen and short chain fatty acid obtained from fermentation and antioxidant effect. Hydrogen and short chain fatty acid are to be compounded to explore effect on the activities in vitro mentioned above of the mixture with different compositions. Based on the results，reference targets can be proposed to reform the structure of KGM further.

氢气的选择性抗氧化作用及对其他生理功能的影响近年获得了突破性进展，膳食纤维摄入并经由肠道菌群发酵产氢是内源性氢气的主要来源，但因在体实验中氢气产生、消除及作用途径复杂而鲜见研究；短链脂肪酸是同时产生的另一类重要产物，但其与氢气共存的生理活性研究尚处空白。本课题的目的是从氢气与短链脂肪酸组合物和选择性抗氧化的新视角，探明不同结构魔芋葡甘聚糖(KGM)通过肠道菌发酵后上述两类产物组成及其活性的差异。课题首先制备并表征不同结构KGM试样；通过体外厌氧发酵，检测它们对人粪便浆水体系中发酵产生氢气和短链脂肪酸的动态影响，比较各组发酵上清液对oOH和ONOO-等自由基的清除能力，观察其是否具有选择性抗氧化作用，并评价对Caco-2细胞毒性和基因毒性，以揭示KGM通过发酵产物影响抗氧化活性的构效关系；通过人工组配氢气和短链脂肪酸混合液，探讨其组成对上述体外活性的影响，为进一步改造KGM结构提供目标参考。

膳食纤维经肠道菌群发酵的代谢产物对人体生理功能的影响近年受到广泛重视。不同结构的魔芋葡甘聚糖经肠道菌群发酵后产生的短链脂肪酸等代谢物的组成及活性差异研究尚处空白。本项目制备并表征了不同脱乙酰度魔芋葡甘聚糖及其降解产物，研究了12个典型魔芋试样对粪便浆水 pH 值及短链脂肪酸组成的影响，进行了魔芋葡甘聚糖结构参数、短链脂肪酸生成量两两相关性分析，探讨了典型魔芋试样对肠道菌群的作用及对肠道嗜酸乳杆菌增殖的影响。研究证实了不同脱乙酰度KGM分子链一级结构、热特性及结晶性能无显著差异；脱乙酰是KGM成凝胶过程的重要步骤，升温促使脱乙酰速率加快，一段时间后脱乙酰度趋于常数，且珠芽魔芋凝胶最终脱乙酰度高于花魔芋。阐明了KOS降低粪便浆水发酵体系的pH 值，且分子量越小，该作用越显著；随发酵时间增长，添加了KOS的发酵液中短链脂肪酸总量逐渐上升，发酵前24小时内，以乙酸增加为主，发酵至36-48小时，丙酸及丁酸产量显著增高；KOS在嗜酸乳杆菌增殖方面有促进作用，2000 Mw的KOS促进L.a体外增殖的效果优于中高分子量KOS；KOS对L.a增殖的最适添加量为2.0%，进一步提高会抑制L.a的增殖。研究还发现KOS与低聚异麦芽糖复配对肠道菌群及经肠道菌群发酵产物又协同增效作用, KOS/IMO复配后促进L.a体外增殖的效果优于单一低聚糖，其中1:1比率下，L.a菌数最高。以上结果揭示了同一来源而被赋予不同精细结构的膳食纤维对肠道菌群的作用及其经肠道菌群发酵产生短链脂肪酸的动态影响，为预测KGM结构改造的方向提供新的思路。