In this study, the fermentation characteristics of high rhamnogalacturonan I pectic polysaccharides (RGI) and free-radical degraded RGI (DRGI) were evaluated by a human fecal batch-fermentation model, and their structural properties were also investigated. As a result, the Mw of RGI decreased from 246.8 to 11.6 kDa, and the branches were broken dramatically. Fermentation showed that RGI degraded faster and produced more acetate and propionate than DRGI. Both of them reduced the Firmicutes/Bacteroidetes ratio and promoted the development of Bacteroides, Bifidobacterium, and Lactobacillus, bringing benefits to the gut ecosystem. However, the composition and metabolic pathways of the microbiota in RGI and DRGI were different. Most of the dominant bacteria of RGI (such as [Eubacterium]_eligens_group) participated in carbohydrate utilization, leading to better performance in glucolipid metabolism and energy metabolism. This work elucidated that large molecular weight matters in the gut microbiota modulatory effect of RGI-type pectic polysaccharides in vitro.
Keywords: gut microbiota; molecular weight; pectic polysaccharides; rhamnogalacturonan I.