A head-to-head comparison of soluble dietary fibers on microbiota composition and short-chain fatty acid production using the in vitro TIM-2 system

Soluble dietary fibers (SDFs) are recognized for their health benefits through their fermentation and gut microbiota modulation. Previous studies focused on individual SDFs without sufficient structural information and a comparative analysis using different SDFs on microbiota composition and function is lacking. The present study aimed to determine key structural features of different SDFs, including soluble resistant starch (SRS), inulin (INU), four structurally diverse pectins (PS1 to PS4), one pectic derivative (PS5) and larch arabinogalactan (AG). Their effects on gut microbiota composition and function were investigated by 72 h experiments in TIM-2 in vitro colon system with pooled feces, upon constant feeding (2.5 mL/h, total of 7.5 g/day) of test compounds. The tested SDFs were structurally different, inducing distinct effects on the relative abundance of specific bacterial genera and overall microbiota composition. AG, PS2, PS3, PS5, and SRS demonstrated marked changes compared to control in the overall community structure over time. SCFA production increased over time for all SDFs, but only PS1 to PS4 resulted in significantly higher SCFA levels compared to control. These findings demonstrate that structurally different SDFs exhibit different effects on the gut microbiota composition and function, however this could not be solely explained by Mw and monosaccharide composition.