Arabinoxylan (AX) is a major hemicellulose fibre component of cereal grains, which makes up around 15 to 30 % of the bran layer and around 1 to 3 % of the endosperm. The polysaccharide is a copolymer of the pentose sugars arabinose and xylose, with the average degree of polymerisation being around 3000 to 6000 units. Fermentation of AX by intestinal microbiota results in the production of short-chain fatty acids (SCFA), which decreases the pH of the colon and improves the growth conditions for beneficial gut bacteria. The SCFA may also act as a source of fuel for the host following absorption. Enzymatic hydrolysis of the AX copolymer creates fragmentation products called Arabinoxylan oligosaccharides (AXOS), that may act as prebiotics and improve the growth of beneficial bacteria such as bifidobacteria in the gut. However, it is unclear if AXOS retains the some of the other beneficial properties of AX.
Researchers are therefore interested in the gastrointestinal effects of supplementing AXOS. To these ends, researchers1 have used a randomised double-blind cross-over study to test the effects of AXOS fortified bread on physiological changes to the gut in 27 healthy volunteers. Subjects consumed 180 g of high fibre wheat and rye bread with or without enzymatically produced AXOS, daily for 3 weeks (~2.14 g/d AXOS). Refined bread without AXOS was supplied for consumption during run-in and wash out periods and acted as a fibre free control. The results showed that AXOS fortified bread significantly increase faecal SCFA and beneficial bifidobacterium concentrations compared to refined control bread. In particular, levels of butyrate were 70 % higher following AXOS fortified bread. Dietary questionnaires showed that subjects consuming the AXOS fortified bread experienced increased stool frequency when compared to the high fibre AXOS free wheat and rye bread.
These results suggest that AXOS fortified bread may have beneficial effect on the health of the gut, in particular through changes to beneficial bacteria, increased faecal transit time and the increased production of SCFA. This supports evidence from studies investigating the physiological effects of fructo-oligosaccharides (FOS), which have similar properties. Traditionally, fibre has been thought of simply as roughage, and its benefits were seen as providing bulk for food transit. However, as nutritional research has progressed, it has become clear that fibre plays a much more diverse and important role in the gut than was previously considered. In particular, fibre appears to play an important role in maintaining proper gut function. Fibre is vital for the proper colonisation of the gut by beneficial microflora and oligosaccharides created by fragmentation of fibre may serve as a useful food for such microorganisms, and as such may provide health benefits.
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