Arabinoxylan‐oligosaccharides (AXOS) affect the protein/carbohydrate fermentation balance and microbial population dynamics of the Simulator of Human Intestinal Microbial Ecosystem

Introduction

In recent years, many research efforts have focused on the modulation of the colonic microbiota and their fermentation processes with the aim of improving host health (Gibson et al., 1989; Cummings and Macfarlane, 1991; Manning and Gibson, 2004). An approach to achieve this goal is the ingestion of prebiotics, food constituents that are not digestible in the upper gut and that beneficially affect the host by selectively stimulating growth and/or activity of one or of a number of health‐promoting bacteria in the colon (Gibson and Roberfroid, 1995). Most of the currently known or suggested prebiotics in the functional food industry are oligosaccharides such as lactulose, fructo‐oligosaccharides (FOS), galacto‐oligosaccharides (GOS), soybean oligosaccharides (SOS), lactosucrose, isomalto‐oligosaccharides, gluco‐oligosaccharides, xylo‐oligosaccharides (XOS) or palatinose (Manning and Gibson, 2004). Recently, arabinoxylan‐oligosaccharides (AXOS) have been proposed as alternative prebiotics (Kontula et al., 2000; Grootaert et al., 2007; Hughes et al., 2007; Vardakou et al., 2007). AXOS with different average degrees of polymerization (avDP, i.e. the average number of xylose residues in their backbone) and average degrees of substitution (avDS, i.e. the average ratio of arabinose to xylose), which may present different prebiotic properties, can be obtained by enzymatic treatment of arabinoxylans (AX) from cereals (Delcour et al., 1999; Swennen et al., 2005; 2006). Arabinoxylans are made up of β‐1,4‐linked d‐xylopyranosyl residues, substituted at the C(O)‐3 and/or the C(O)‐2 position with monomeric α‐l‐arabinofuranoside. Ferulic acid can be coupled to the C(O)‐5 of arabinose through an ester linkage (Goesaert et al., 2005). These structural elements are also present in AXOS.

Colonic fermentation is an anaerobic process in which carbohydrates and proteins are metabolized by the microbiota of the large intestine. The intestinal microbiome mainly consists of nine bacterial phyla of which Firmicutes, Bacteroides and Actinobacteria are dominant, and plays a key role in obtaining energy from otherwise indigestible compounds (Rajilić‐Stojanovićet al., 2007Turnbaugh et al., 2007). Whereas fermentation of carbohydrates is generally accepted to be beneficial for the host due to the generation of short‐chain fatty acids (SCFA), fermentation of proteins results in the formation of potentially toxic metabolites such as ammonium ions, indoles, phenols or amines (