The molecular weight, solubility and viscosity of oat beta-glucan affect human glycemic response by modifying starch digestibility

► The physicochemical properties of β-glucan influence in vitro starch digestibility. ► As the viscosity of β-glucan increased, the starch digestibility was reduced. ► This effect correlates to β-glucan bioactivity in reducing glycemic responses. ► When the starch digestibility decreased, glucose responses were lowered. ► Higher reduction in glucose responses were found at higher β-glucan/starch ratios. The interaction between oat β-glucan and other food components has the potential to influence starch digestibility and consequently affect its bioactivity in reducing glycemic responses. Blood glucose concentrations were measured before and after ingesting wheat and oat granolas, with 0.6 and 6.2g of β-glucan, respectively, and two starch doses (40 and 60g). As the in vitro extract viscosity of β-glucan increased, the in vitro starch digestibility was reduced and the glucose responses were lowered. The peak blood glucose response (PBGR) and the incremental area under the curve (iAUC) were lower in the 40g than in the 60g starch formulation. β-Glucan was significantly more active in reducing PBGR and iAUC when the β-glucan/starch ratio was 1.6:10 rather than 1.1:10. This information is valuable for new product development and for quality assessment of bioactive foods containing oat β-glucan.