An analysis of the structural diversity of the principal component of dietary fibre in different varieties of wheat has been carried out, enabling breeding programmes to better take account of this important but complex component. Researchers from the Institute of Food Research and Rothamsted Research, which are strategically funded by BBSRC, have used a variety of imaging techniques to characterise structural and spatial differences in arabinoxylan content. Ensuring our food has sufficient nutrition content is as important to overall food security as increasing the amount of food available, and this research could be used to breed improved varieties or produce natural healthier food ingredients.

Dietary fibre is an important part of a healthy diet, and one of its main sources is cereal grains. In wheat, the majority of fibre is derived from the cell wall material, a major component of which is a long-chain sugar called arabinoxylan. Arabinoxylan comprises both viscous soluble and insoluble forms of fibre, and has benefits to human health, such as in slowing the rate of digestion, contributing to reducing appetite and nourishing the beneficial bacteria in our gut. The arabinoxylan content also affects the properties for bread making and other food uses, and can have detrimental affects for livestock and poultry feed and for malting, distilling and biofuel production, and so is considered an important quality factor in wheat.

Despite this importance, we do not have complete understanding of the genetic basis for variation in arabinoxylan content in different varieties of wheat. One reason for this lies in the arabinoxylan molecular structure, which is highly heterogeneous.. It is a branched molecule consisting of a backbone with associated side residues which vary in number and distribution.

To try to understand this variation, the researchers, with colleagues at INRA, the French National Institute for Agricultural Research, examined wheat cultivars that were grown as part of the HEALTHGRAIN Diversity Collection. This collection was grown in Hungary in 2004-5, as part of HEALTHGRAIN, an EU-funded project that aimed to improve health and well-being by producing healthier foods and ingredients from cereals. Part of this included a survey of the levels of a range of bioactive compounds in different wheat varieties, including fibre components.

The researchers selected fifty wheat cultivars from this HEALTHGRAIN collection representing wide variation in total arabinoxylan content. To determine how the total content related to the structure of the complex arabinoxylan, the researchers used FT-IR spectroscopy of thin sections of the grain. This technique shows the distribution of arabinoxylan in the cell walls within different parts of the grain, and also provides information about the diversity of the arabinoxylan structure. Complementary data was obtained using a novel ¹H NMR spectroscopic technique, which enabled the proportions of associated side residues to be determined.

The researchers found considerable variation in the composition and structure of arabinoxylan between different wheat varieties.  These differences may have implications for the processing qualities of the different varieties, and this new knowledge could help breeding programmes to maintain or improve these properties. This variation in arabinoxylan structure affects its solubility and viscosity, and so influences the health-promoting effects associated with dietary fibre. The diversity identified in this study can also therefore provide a basis for wheat breeders to develop varieties with enhanced health benefits.

The study also demonstrated that forms of cell wall arabinoxylan are not uniformly distributed throughout the grain which opens up the possibility of preparing flours with different contents and forms of arabinoxylan by milling. During milling, different parts of the grain are separated to produce different types of flour. The information on variation in arabinoxylan amount and composition both between varieties and within the grain of single varieties could therefore be used to design additional mill streams containing enhanced levels of the healthiest arabinoxylans, adding value to the production and milling of the grain and providing a natural source of healthier food ingredients.

Reference:

Spectroscopic analysis of diversity of arabinoxylan structures in endosperm cell walls of wheat cultivars (Triticum aestivum) in the HEALTHGRAIN diversity collection. Toole G. A. et al Journal of Agricultural and Food Chemistry 59(13) 7075-7082  doi: 10.1021/jf201095m

Funding:

BBSRC, the European Commission in the Communities 6th Framework Programme, Project HEALTHGRAIN (Food-CT-2005-514008)