Abstract
This project was designed to provide new insights into the mechanisms by which plant cell walls (‘dietary fibre’), influence starch bioaccessibility (‘release’) and postprandial glycaemia. Cell walls were hypothesised to limit bioaccessibility by acting as physical barriers to digestive enzymes, and/or by limiting the gelatinisation of starch during hydrothermal processing, with major implications for starch digestion kinetics and consequently, postprandial metabolism.Chickpeas and durum wheat were milled to create test materials with varying degrees of structural integrity (i.e., amounts of encapsulated starch). The starch digestibility and behaviour of these milled materials were studied in vitro, and the data obtained were used to develop a mathematical model of starch digestion. Finally, a postprandial ileostomy study (n=9) was carried out to determine the effects of encapsulation on in vivo starch bioaccessibility, and blood glucose, insulin, lipid, and gut hormone responses.
Cell wall permeability and starch gelatinisation studies provided new evidence for the role of cell walls as barriers to digestive enzymes and as restrictors of starch gelatinisation. In vitro digestibility studies of hydrothermally processed materials, and subsequent Logarithm of Slope analysis, indicated that the rate and extent of digestion was strongly affected by cellular integrity. In vivo, the ingestion of coarsely milled wheat endosperm (~62% encapsulated starch) decreased the glycaemic response by ~30% compared with the ingestion of finely milled endosperm (i.e., containing the same amount of starch but not encapsulated).
Overall, intact cell walls significantly limit starch bioaccessibility, and reduce the postprandial rise in glycaemia and insulinaemia. The differences in digestibility and glycaemia between chickpeas and durum wheat were explained by their contrasting cell wall properties (e.g., permeability and fracturing). This work provides clues as to how plant materials may be manipulated in order to generate new functional food ingredients or products, for instance with slow-release or prebiotic effects.
| Date of Award | 1 Sept 2014 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Peter Ellis (Supervisor), Peter Butterworth (Supervisor) & Sarah Berry (Supervisor) |