Exploring the relationship between the structure of wheat dietary fibre and prebiotic activity

Abstract:

Cereal dietary fibre has well-established health benefits in terms of reducing serum cholesterol and CVD and reducing the incidence of colon cancer (Aune et al, BMJ, 2011; 343:d6617doi:10.1136/bmj.d6617). The mechanisms of these effects are poorly understood but it is likely that pre-biotic fermentation in the colon is a contributory mechanism. Previous collaborative studies between the applicant’s laboratories have shown that the major dietary fibre component in wheat grain, arabinoxylan (AX), has pre-biotic activity which is related to mass (Hughes et al, J Agric Food Chem 2007). The present studentship will explore these relationships in more detail using transgenic lines and genetic stocks and new analytical approaches to identify the products of pre-biotic fermentation. It will also build on a new Reading:Rothamsted IBTI grant focused on developing new prebioitics from DDGS.

Background:

Wheat derived AX fractions have been shown to act as prebiotics in the colon, increasing populations of Bifidobactrium spp/and or Lactobacillus spp. (Hughes et al. J Agric Food Chem, 2007). There is a growing body of evidence that suggest that these compositional shifts in the gut microbiota and the subsequent production of short chain fatty acids from AX fermentation improve overall health (recently reviewed by Broekaert et al. Crit Rev Food Sci Nutr, 2011). Such improvements include favourable modulations in glucose and lipid metabolism, appetite regulation and improved immune function and resistance to enteric pathogens. The insoluble fibre fraction of AX has also been shown to increase faecal bulk and reduce transit time.

The main polysaccharide of wheat grain cell walls is arabinoxylan (AX), making up some 70% of total cell wall material. The structure of AX however, differs between tissues. The outer layers containing highly substituted and cross-linked forms and the starchy endosperm and aleurone having similar structures of xylan chains mono- or disubstituted with arabinose (Fincher and Stone. Advances in Cereal Science and Technology, 1986) The amounts and structure of AX polymers also differ between wheat cultivars. A recent large survey of cereal AX as part of the EU-funded HEALTHGRAIN project (Gebruers et al, J Agric Food Chem, 2008) highlighted the natural range of variation in the amount of AX in 150 wheat lines. Selected lines were then grown over 3 years on four sites across Europe and their AX contents measured. It was also determined that a substantial proportion (more than 60%) of the variation in total dietary fibre content was heritable (Shewry et al. J. Agric. Food Chem. 2008).

We have determined the total (TOT-AX) and soluble AX (water-extractable, WE-AX) content from flour extracts in the progeny from a cross between the Chinese variety, Yumai-34 (highest AX) and the Hungarian Ukrainka wheat (a low AX containing cultivar) and also in a series of Turkish wheats, which have shown even greater variation in AX content. We have also been able to manipulate the structure of AX in a series of transgenic wheat lines using RNAi of glycosyl transferase genes that are responsible for their biosynthesis (Anders et al, 2012, PNAS doi/10.1073/pnas.1115858109). Therefore, the possibility exists to produce AX fractions, with known structures and determine whether they have high prebiotic activity.

Supervisors:

Alison Lovegrove / Peter Shewry / Dimitrios Charalampopoulos

Location/s:

Rothamsted Research / University of Reading