Interaction of cellulose and xyloglucan influences in vitro fermentation outcomes

•Cellulose-xyloglucan (BC-XG) interactions affect fermentation in multiple ways.•Fermentation of both XG (rate) and BC (extent) enhanced in physical mixtures.•BCXG composites ferment differently to a physical mixture of BC and XG.•XG fermented less and cellulose more in BCXG than in BC and XG mixture.•Differences consistent with microbial community and short chain fatty acid changes. To investigate the effects of interactions between cellulose and xyloglucan (XG) on in vitro fermentation, a composite of bacterial cellulose (BC) incorporating XG during pellicle formation (BCXG), was fermented using a human faecal inoculum, and compared with BC, XG and a mixture (BC&XG) physically blended to have the same BC to XG ratio of BCXG. Compared to individual polysaccharides, the fermentation extent of BC and fermentation rate of XG were promoted in BC&XG. XG embedded in the BCXG composite was degraded less than in BC&XG, while more cellulose in BCXG was fermented than in BC&XG. This combination explains the similar amount of short chain fatty acid production noted throughout the fermentation process for BCXG and BC&XG. Microbial community dynamics for each substrate were consistent with the corresponding polysaccharide degradation. Thus, interactions between cellulose and XG are shown to influence their fermentability in multiple ways.