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Understanding the effect of soluble fibres on the hydrolysis of starch and the diffusion of glucose during simulated human digestion

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Title: Understanding the effect of soluble fibres on the hydrolysis of starch and the diffusion of glucose during simulated human digestion
Author: Fabek, Hrvoje
Department: Department of Food Science
Program: Food Science
Advisor: Goff, H. Douglas
Abstract: Dietary fibre consumption is associated with a wide range of health benefits including reductions in postprandial glycemia. It is widely accepted among researchers that the effect is due to an increase in viscosity that fibres exert along the gastrointestinal tract; however, the mechanism remains to be elucidated. In this study, protein-starch solutions were fortified with four types of soluble fibre – xanthan gum (XG), guar gum (GG), soluble flaxseed gum (SFG) and soy soluble polysaccharide (SSPS). Subsequently, all solutions were passed through a three-stage in vitro digestion model. Rheological investigations and calculated Power Law parameters showed that all solutions behaved as pseudoplastic shear-thinning materials and exhibited solid-like behaviour. Their rheological behaviour was variably influenced as the treatments were hydrolysed where XG retained a significant amount of its initial viscosity and remained a viscoelastic gel despite the secretions of the simulated digestion model. Quantitative analyses of reducing sugar release (RSR) demonstrated an inverse trend between RSR and digesta viscosity. Glucose release measurements revealed that even low viscosity systems were effective at lowering the hydrolysis of starch. Analysis of glucose diffusion using a dialysis system indicated a lesser effect and only the fibres with a measurable G’ and higher viscous component inside the simulated small intestinal stage were able to attenuate glucose diffusion. Native (uncooked) tapioca starch granules were separated, purified and dried at different times of digestion and analyzed for changes in particle size using light scattering and starch morphology using scanning electron microscopy (SEM) and light microscopy. Most granules were in the range of 5-50µm, with an apparent reduction in particle size as hydrolysis continued. SEM images of starch granules revealed smooth surfaces in solution and substantial degradation (exo- and endo-corrosion, with some granules becoming completely hydrolysed) as the treatments progressed through the in vitro digestion. The progression of morphological changes was attenuated in granules extracted from the digesta of XG and GG. Light scattering and microscopy also revealed an aggregation effect between granules extracted from the XG and GG treatments. The results of the study indicated that the mechanism by which soluble fibres are able to moderate the in vitro glycemic response may be multi-faceted. Moreover, they may not be due to viscosity alone as other effects may be important, including the ability of fibres to create and maintain gel networks inside the lumen and allow starch granule aggregation.
Date: 2015-04
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