Effects of molecular weight on simulated digestion and fecal fermentation of polysaccharides from longan pulp in vitro

The gastrointestinal digestion and fermentation in vitro of longan polysaccharide (LP) and its degraded products (DLP-1, DLP-4, and DLP-8) with different molecular weights (Mw) were investigated. Results indicated that four polysaccharides were only slightly degraded in the gastrointestinal digestion and mainly utilized by gut microbiota in the colon. Among them, DLP-8 with the lowest Mw was easily utilized by intestinal bacteria accompanied by the highest production of acetic and butyric acids. The DLP-8 group exhibited the best growth of beneficial bacteria including Dialister, Bifidobacterium, and Bacteroides. Correlation analysis further verified that the modulatory effect of longan polysaccharide on gut microbiota was structure-dependent, and Mw performed a key role in selectively regulating gut microbial composition. These results showed the smaller Mw longan polysaccharides were more readily fermented leading to modulation of gut microbiota in vitro.