The effect of viscous soluble dietary fiber on nutrient digestion and metabolic responses Ⅰ: In vitro digestion process

The consumption of viscous soluble dietary fibers (VSDF) as thickening agents for beverages and fluid foods has increased with their ability to modulate postprandial glycaemic response due to increasing digesta viscosity. The present study was designed to establish appropriate VSDF viscosity that can beneficially modulate nutrient digestion and attenuate glucose release and absorption. The effects of xanthan (XG), guar gum (GG) and locust bean gum (LBG) on the digestibility of starch and protein in beverages with initial low viscosity (300 mPa s, 30 s⁻¹) and high viscosity (1500 mPa s, 30 s⁻¹) were investigated using the proposed Infogest simulated digestion model. Moreover, the effects of dilution, physiological pH and enzymatic activities on viscosity decrease of three gums during digestion were evaluated. The results showed that at the end of intestinal digestion, XG showed the highest viscosity at low and high viscosity followed by GG and LBG, respectively. During the intestinal digestion process, three gums have little effects on protein and starch digestion at low viscosity. However, all the gums significantly reduced nutrient digestion at higher viscosity, and XG exhibited the best performance in reducing the amount of glucose and free amino acid released. The digestion rates of protein and starch showed a linear relationship with the viscosity of the system. Similarly, the amount of glucose diffused as a function of time was most significantly (p < 0.05) decreased by XG followed by GG. At low and high initial viscosities, dilution of the gastrointestinal contents was the most important source of viscosity reduction for all gums, and XG was the most resistant to dilution and recorded the least viscosity drop. These observations suggested that XG with high viscosity may serve as a useful food ingredient to attenuate postprandial glucose spikes in human.