Effect of In vitro Human Digestion on the Viscosity of Hydrocolloids in Solution: A Dietary Fibre Study

January 1, 2011 Human Health and Nutrition Data 0 Comments

Effect of In vitro Human Digestion on the Viscosity of Hydrocolloids in Solution: A Dietary Fibre Study

Year: 2011
Authors: Hrvoje, F.
Publication Name: University of Guelph
Publication Details: MSc. Thesis; Unpublished


The effects of a simulated in vitro digestion model on the viscosity of solutions of locust bean gum, guar gum, fenugreek gum, xanthan gum, gum Arabic, psyllium, flaxseed gum and soy soluble polysaccharides (SSPS) were examined in this study. All hydrocolloid solutions were formulated for low viscosity (LV), medium viscosity (MV) and high viscosity (HV), which were subsequently subjected to 3 treatments of equal volumes each. The treatments consisted of 1) H2O dilutions, 2) acid and alkali in the absence of enzymes/bile and 3) an in vitro digestion model simulating the gastric and duodenal phases with pH changes in the presence of hydrolytic enzymes and bile salts. All hydrocolloids showed substantial reductions in viscosity, with dilutions exerting the greatest effect. Depending on the concentration, xanthan gum retained 20 to 50percent of its initial viscosity while the other solutions were in a lower range of 1 to 16percent, thereby showing considerable resilience to the 3 simulated conditions. (Authors abstract)
The deficiency of North American dietary fibre consumption may be related to the texture and palatable quality that foods rich in fibre deliver, or more importantly do not deliver. Viscosity is a technological feature of many hydrocolloids which, when acting as dietary fibre, have shown to promote many health benefits including reduction of post-prandial glycemia. High viscosity can lead to over texturization of foods. Moreover, the viscous nature of any food product inadvertently changes once consumed. The viscosity of dietary fibre is believed to be an essential tool in lowering the risk factors for T2 diabetes. In this study various hydrocolloids such as guar gum, locust bean gum, fenugreek gum, xanthan gum, flaxseed gum, soy-soluble polysaccharides and gum Arabic, which are novel fibre sources, were evaluated for their contribution to viscosity in various concentrations both in solution and after in vitro digestion, mimicking the upper gastrointestinal tract to ascertain how well the viscosity is retained through the digestion process. Locust bean gum, guar gum, fenugreek gum, xanthan gum, gum Arabic, psyllium, flaxseed gum and SSPS all showed significant viscosity reductions when exposed to the conditions of dilutions, acid and alkali, and the in vitro digestion model. For the most part, there was no difference between the treatments therefore highlighting that a dilution effect is the cause of lowering fibre viscosity, with minimal to no effect being attributed to pH changes or the action of digestive enzymes. Depending on the hydrocolloid studied, the severity of the observed effects on solution viscosity varied.  Upon comparison of all the substrates studied, xanthan gum demonstrated the greatest ability to resist structural changes after simulating the 3 conditions, as it was able to maintain viscosity more so than all others. The reduction in viscosity of gum Arabic, flaxseed gum, and SSPS, were substantial. Consequently, this could imply that xanthan gum and some galactomannans may be more biologically functional in terms of modulating certain physiological responses, such as postprandial glycemia or cholesterol reductions, in comparison to the low-viscosity fibres that showed considerable losses in structural integrity.  The present study demonstrated that viscosity is greatly affected by the conditions present in the GI tract, generating extensive reductions in all hydrocolloids studied. Moreover, the extent of these losses is influenced by the structural properties possessed by each of the fibres. As an extension, it could be assumed that the viscosity profile that is prevalent in the small intestine is the one that should be used to characterize a structure function relationship of any soluble dietary fibre. This leads to the proposal for future research. Having characterized the flow behaviour of different hydrocolloids both before and after in vitro digestion, it would be essential to tie the findings in with a physiological response, such as glucose mobility as measured by adding starch. (Editors comments)

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