Non-invasive microstructural characterization and in vivo glycemic response of white bread formulated with soluble dietary fiber

The global prevalence of diet-related chronic diseases, such as obesity and type 2 diabetes, has prompted the development of starchy foods with functional ingredients to control starch digestibility and promote health benefits. This study aimed to analyze the effect of a mixture of soluble dietary fibers (SDF) - inulin and methylcellulose - on microstructural changes, in vitro starch digestibility, and in vivo glycemic response of a wheat bread formulation. Quantitative micro-CT image analysis revealed a reduced bread porosity, increased pores with small diameters, and a significant rise in bread structure thickness (p < 0.05), indicating a more homogeneous and compact structure after adding the SDF blend. The addition of the SDF blend led to a reduction in in vitro starch digestibility in the bread. The rapidly available glucose decreased from 31.02 g/100 g to 11.52 g/100 g, and the unavailable glucose fraction increased from 62.81 g/100 g to 80.49 g/100 g in bread + SDF compared to regular bread (p < 0.05). These differences could be attributed to the observed fiber coating over the starch-gluten network in these samples, which may act as a physical barrier, impeding starch digestibility. In line with these findings, the SDF blend significantly reduced the postprandial glycemic response of bread by up to 25% compared with Trutol® standard commercial glucose (p < 0.05). The new formulation could be classified as an intermediate glycemic food, as glycemic index and glycemic load were 56.43 and 15.11, respectively, which may be helpful for people who want to manage the glucose levels in their daily diets.