Mining diversity in cereal (wheat) fibre to improve the nutritional quality of bread

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Wheat is the major food crop grown in the UK. A substantial proportion is used for human consumption, making it an important source of calories, protein, minerals, vitamins and dietary fibre in the human diet. Consumption of fibre is linked to decreased risk of cardiovascular diseases, certain types of cancer, (such as colon and breast) and type-2-diabetes. Cereal-based foods, in particular bread, are a staple in the UK diet and represent one of the major sources of carbohydrate. Whilst there have been drives to increase consumption of wholegrain and wholemeal products, many consumers still prefer the texture and appearance of white bread. Manufacturers are addressing this through processing, using novel fibre-derived ingredients and white wheats to give breads supplemented with bran the appearance of white loaves. However, the value of doing this nutritionally has yet to be demonstrated for each product. White bread is an important UK foodstuff, but being a starchy food which is rapidly broken down to glucose it has a high glycaemic index (GI). Wholemeal bread contains a higher level of dietary fibre, which is considered to be healthier, but forms only a small fraction of the bread eaten in the UK. Dietary fibre contains two components; soluble and insoluble, with the major soluble component in wheat being a fraction known as arabinoxylans (AX), which make up ~70% of wheat endosperm cell wall polymers. The mechanism by which fibre acts is not clear - although there is evidence that its effect is to change the viscosity of the material in the stomach and gut, slowing absorption of nutrient into the body. The aim of this grant is to identify the mechanism for the effect of fibre by studying the effect of changing AX strucutre and solubility. We will first grow (at Rothamsted) four wheats lines which have been shown in previous Rothamsted and IFR collaborative work to have very different AX contents. These will be milled into flour and made into loaves using standard methods at Campden BRI, the UK centre for baking. Grains, flour and breads will be studied to find out what happens to the AX during the breadmaking process, using novel methods developed at IFR and Rothamsted. In addition, we will develop and unify existing equipment at IFR and Birmingham; a model stomach at IFR and a model gut at Birmingham, into a form where it can be used to simulate gastric and duodenal digestion, and study how the cell wall components behave through simulated digestion processes. Using these methods we will be able to identify and explain the effects of AX, and then design breads which have a healthier human response. The final stage of the project will be a human trial of these breads which will allow us to validate our approach. Outcomes will thus be (i) understanding of some of the ways to make white bread more healthy, as well as (ii) a validated model for digestion, and (iii) understanding the role of AX in dietary fibre. This understanding can be used in the validation of health claims as well as in the developments of new grains, processes and products and the model digestion systems will help the food industry to explore new healthier food formulaitons in a more cost-effective manner.