In vitro fermentation of onion cell walls and model polysaccharides using human faecal inoculum: effects of molecular interactions and cell wall architecture

Abstract Plant primary cell walls provide a primary dietary source of fermentable carbohydrates. They are typically based on a cellulose network cross-linked by xyloglucan, with pectin incorporated, but the relative contributions of components and their architectural arrangement to gut fermentation performance is incompletely understood. Onion cell walls (OCW) were isolated and used as a primary cell wall model. OCW, models for their main constituents (xyloglucan, pectin, cellulose) and the physical mixture of these model polysaccharides (Mix) were fermented in vitro up to 48h, using a human faecal inoculum. Each constituent in Mix was fermented to a similar extent as single-component substrates, with comparable gas and short chain fatty acid (SCFAs) production. The microbiota responded differently and specifically to each polysaccharide, with the microbial community for Mix reflecting both pectin and xyloglucan. OCW was degraded more slowly at the early stage of fermentation, with less SCFAs produced compared with Mix, though a more extensive fermentation occurred by the end of fermentation, due to the slow but essentially complete fermentation of cellulose in OCW but not Mix. Microbiota shifts for OCW were different to those for Mix. The architecture of OCW as well as polysaccharide composition determined both fermentation outcomes and microbial community shifts.