The effects of removing endogenous proteins, β-glucan and lipids on the surface microstructure, water migration and glucose diffusion in vitro of starch in highland barley flour

The effects of removing non-starch components on the surface microstructure, water migration and glucose diffusion rate of highland barley starch (HBS) were systematically studied to reveal the models that affect the digestibility of HBS. The results of scanning electron micrographs, confocal laser scanning microscopy, polarization cross and particle size distribution showed that there were two particle size ranges in highland barley flour, large (73.99–591.90 μm) and small (<73.99 μm). Partial β-glucan and proteins form a compact and continuous matrix on the surface of HBS granules; lipids can partly be adsorbed on the surface of HBS granules, while other lipids, proteins and β-glucan are scattered around HBS granules. After the removal of non-starch components, the ratio of large particles decreased and the starch granules were more exposed, especially proteins and β-glucan. The results of low-field nuclear magnetic resonance investigation showed that the water migration rate was accelerated after the removal of β-glucan, and partial free water was transformed into weakly bound water, while the opposite effect was observed for the removal of proteins and lipids. The glucose diffusion rate in vitro was unchanged after the removal of lipids, while the removal of β-glucan significantly accelerated the diffusion of glucose in vitro. This study reveals that the effective models of HBS inhibited by non-starch components is the compact matrix mainly formed by proteins and β-glucan on the surface of HBS granules. Additionally, the rate of glucose diffusion across the small intestinal wall could be considered as one of the means of constructing slowly digestible starch.