The Role of Plant Cell Walls in Regulating Starch and Lipid Bioaccessibility from Plant Foods: In Silico In Vitro and In Vivo Studies

Most people commonly eat plant foods rich in starch, notably cereal products (e.g. bread, rice), and also some that are rich in fat (e.g. tree nuts). However, little is known about how such foods release starch and fat in the human gut and how, in turn, this may influence digestion and ultimately the absorption of nutrients into the body. Improving our understanding of these processes is important for basic scientists studying the behaviour of foods in the gut and their effects on metabolism. It is also important for health professionals and policy makers that are worried about excessive food consumption and the growing problem of obesity and associated problems of heart disease and diabetes. Moreover, the rate and extent of starch and fat digestion and absorption into the blood stream are important factors in altering the risk of heart disease. The release of fat and starch from plant foods and the digestion and absorption of these nutrients by the body are highly complex processes. Our progress in understanding these processes is impeded by the hugely complex structure and properties of plant foods and individual nutrients. Our project proposal brings together a unique combination of world experts from different institutions and disciplines. These experts have formed a large team in order to improve our knowledge of how edible plants behave in the gut and how the gut reacts to the starch and fat available for digestion. For example, it is important to know about the rate at which nutrients are released from plant foods as they move along the gut, since this will affect the time course of digestion and absorption. This in turn will influence the way the nutrients are metabolised within the body. We currently study almond nuts and cereals, e.g. wheat, to see how fat and starch are released from plant tissues. Starch, fat and other nutrients are found inside numerous cells that make up the plant tissue, e.g. an almond seed contains about 50 million cells. Such cells are very small in size, often with a diameter of less than about one tenth of a mm. One significant factor that seems to affect nutrient release from plant cells is the presence of cell walls, more commonly referred to in nutrition as 'dietary fibre'. How starch and fat are released from these cells is poorly understood. Initial studies will involve examining the role of cell walls as physical barriers in controlling the release and digestion of nutrients, using various methods to examine plant tissue at a cellular scale. One novel method will be the use of a recently established 'Dynamic Gastric Model', a computer-controlled simulation of digestion in the human stomach. We will also feed human volunteers with the same plant foods rich in fat and starch, to determine the effects of processing and mastication on nutrient release and digestion and the rate at which digested nutrients are transported into the blood stream. Finally, we will also produce a mathematical description of how fat and starch are released from edible plant tissues during digestion. It is envisaged that in the future, the use of mathematics will allow research scientists to predict the behaviour of similar foods in the gut without having to do so many laboratory experiments. This work will help the food industry to produce new food products or ingredients that have a controlled release of starch and fat in the gut, which could, for example, help to reduce the risk of heart disease. Indeed, Premier Foods, a large food manufacturer, has agreed to collaborate with us and provide scientific and technological expertise. Premier Foods has also agreed to provide cereals (e.g. wheat) and food products made with these cereals, all of which have been specially prepared to control starch release. These raw materials and food products will be used in our project to study how they behave in the gut and assess their potential benefits in reducing the risk of heart disease.

The release ('bioaccessibility') of starch and lipid from plant foods in the gut plays an important role in influencing starch and lipid digestion, postprandial metabolism and gut hormone signalling. However, the mechanisms of nutrient release from plant food matrices are largely unexplored. Moreover, there have been no fundamental studies on the role of plant cell walls (PCW) in influencing nutrient release. The aim of this project is to understand how PCW ('dietary fibre') of exemplar foods (almonds and wheat) influence the bioaccessibility and digestion of intra-cellular starch and lipid and consequential effects on postprandial metabolism in humans. A multidisciplinary approach will be used, involving a novel combination of in silico, in vitro and in vivo methods to study starch and lipid bioaccessibility, digestion kinetics and postprandial metabolism. A mathematical model will be developed for predicting nutrient release from plant tissues using geometric theory and empirical data from microstructural analysis of plant materials and digestion studies. Model gut simulations of digestion will be used to study the effects of processing, mastication and gut environment on starch and lipid release and the role of PLW. Kinetic experiments on separated plant cells will be conducted to determine if amylase and lipase penetrates PCW and hydrolyses intra-cellular starch and lipid, respectively. In human studies, the effects of chewing and digestion on lipid release will be determined. Effluent from ileostomists will be used to quantify starch and lipid loss at the terminal ileum and examine 'digested' plant tissue microstructure. In human metabolic studies, we will also determine the effects of lipid and starch release on postprandial glycaemia, insulinaemia, lipaemia, and gut peptides GIP, GLP-1 and CCK. These studies will provide basic information to support the design of foods with starch and lipid absorption profiles beneficial to cardiovascular ageing.

The proposed research will be beneficial to relevant stakeholders outside the academic communities, including the commercial sector, public sector bodies (e.g. FSA) and the general public. Our work is likely to be particularly useful to food companies and may lead to innovative applications in the future, such as the engineering of 'functional ingredients and foods'. The design of foods made from raw ingredients with controlled and predictable nutrient release would benefit public health. The main beneficieries will be the DRINC members and Premier Foods (PF), our industrial partner. PF claim that our research work could potentially lead to the use of raw ingredients (e.g. cereals) in snack and bakery products with predictable nutritional properties. PF could also benefit from the use of the bioaccessibility and digestion models, which have potential use in the screening of raw ingredients, especially for novel products with a health claim. One advantage with using such models is that they should reduce the number of expensive human studies. This would be of considerable value to PF in view of its interest in improving consumer health and the development of health claims under EU regulations. The research also has potential impact on DRINC members using raw ingredients for producing nutritionally-enhanced cereal products or products containing other edible plants. The research should also help policy-makers in formulating new dietary advice and guidelines from new data on plant foods. The applicants regularly give talks at schools and media interviews about their research. The applicants will interact with members of DRINC by having regular meetings to discuss on-going research during the project. There will also be regular meetings between the academics and the team at PF to discuss research findings. This will build on existing contacts with PF, since the applicants already collaborate on studies of whole grain cereals. To optimise interaction with PF, the research staff and PhD student on the project will spend time working at PF's research centres in Lichfield (Holgran) and High Wycombe (Premier Analytical Services). The academic centres have websites providing information on research projects; KCL has College School and Divisional websites, which are regularly updated by designated staff. The applicants will take steps to ensure that outcomes are highlighted along with publicity about publications arising from the research work. The research centres also have public relations departments dealing with media publicity. For the DRINC, a BBSRC external co-ordinator will monitor the progress of the project and also facilitate networking between the applicants and industry. The existing collaboration between the applicants and PF will continue throughout the period of the grant. PF have agreed to provide in-kind support for technological expertise and assistance for milling of cereal endosperm, characterising.