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

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.

This project will provide mechanistic understanding to allow selection of wheat varieties or ingredients for producing breads with improved nutritional quality. The solubility of wheat cell wall polysaccharides, such as aribinoxylans (AX) in the upper GI tract lumen must be a function of (i) At the crop level: the intrinsic properties of cell wall polysaccharides, primarily a function of genetic effects which may be modified by growing environment; (ii) At the process level: milling and baking which may modify cell walls in as yet undefined ways; (iii) At the human level: the upper GI tract luminal environment We will investigate how such factors affect the health benefits of soluble cereal fibre (AX), by (i) growing grains which are known to have different AX contents, (ii) making flour and baking bread from these grains, (iii) analysing the materials using new chemistry and imaging technologies, (iv) conducting in-vitro digestion studies using a novel in-vitro digestion system, thus (iv) identifying breads with different digestion behaviours which will then be tested on humans to confirm their effects. Hypotheses to be tested are that (i) Changes in the viscosity of digesta that affect nutrient availability and uptake can be generated by solubilisation of AX, and (ii) The amount and availability of these fractions is affected both by grain type and the milling and baking process; Identification of breads with healthier digestion profiles, and explanation and quantification of this will enable innovation through knowledge-based rather than empirical approaches in (a) plant breeding, through selection of optimal grain traits (b) changes occurring during manufacture through different baking methods and (c) fundamental science through identification of factors controlling digestion.

With the prevalence of food related diseases reaching epidemic levels, the adverse effects on the health and quality of life to the public is profound. In addition a crude estimate of the cost of food related ill health to the NHS is about £4 billion annually. The Obesity Foresight report estimates the cost to the nation in the order of £50 billion in 2050. In this work we will increase understanding of digestion and build a theoretical framework for it. This will allow science driven design of food formulations to address some of the major food related diseases. We extend and apply existing knowledge to produce and validate a healthier white bread, which is one of the staple foods in the western world. Overall this work will give tools for knowledge-based design of formulations with improved health attributes, and addresses Areas 1 (food structure and physiology) and 2 (processing and delivery) of the BBSRC DRINC call. It also addresses priorities in the BBSRC Strategy for Food. The impact of this research is potentially considerable: (i) to the food industry both within DRINC and outside. White bread is a major component of the UK diet but its health benefits could be improved by reducing its GI. One means of achieving a reduction in GI might be to alter the viscosity of bread digesta, which might be achieved by the addiiton of soluble dietary fibre. However the mechanism of action of dietary fibre is not fully understood. The aim of this grant is to identify the role of AX and its physicochemical properties may alter viscosity of bread digesta, and to show the extent to which breads prepared from wheat lines with different AX compositions and properties, have different digestion profiles, particularly wiht regards glucose release. This will provide validated and quantified data to underpin health claims for the use of dietary fibre in bread. Such data will affect industry by; - allowing substantiation of health claims for breads with different GI; - allowing plant breeders, millers and bakers, to identify wheat cultivars which can be selected and grown with the aim of incorporation into healthier products. This new knowledge could support (through activities of, for example, the Wheat Genetic Improvement Network (WGIN; the Stakeholder forum is chaired by Peter Shewry [RRes]) optimal use of wheat cultivars for improving the nutritional quality of bread, and might also support future development of high-throughput screening approaches for selecting new varieties; - suggesting routes by which the beneficial health properties of AX in cereals might be maintained or enhanced through the milling and baking process (although we will study only the industry-standard baking process, Campden BRI have a wealth of know-how which could be used to suggest modifications); - enable new products to be marketed which have healthier digestion profiles whilst maintaining the consumer wish for white bread; (ii) Pharma and other industries: Similar in-vitro and in-silico models of digestion, albeit much simpler in nature, have been used by the pharma industry, for example to quantify dissolution of drugs. The models developed in this project could be extended to design and validate targeted delivery of enteric drugs. As demonstrated from the use of the IFR Dynamic Gastric Model from the pharma industry such interest exists and both sectors would benefit from possible synergies. (iii) Consumers: Diet-related diseases have reached epidemic levels with detrimental effects to the quality of life of individuals. Changes in diet and eating habits therefore represent an important aspect of prevention of diet-related diseases. By understanding digestion phenomena occurring in-vivo it may be possible to provide to consumers white bread that have advanced health benefits which are good to eat.