Effects of yeast β-glucan on the digestibility of extruded corn starch with varying amylose contents

Polysaccharides have been widely reported to reduce starch digestibility. However, most studies primarily attribute this effect to viscosity enhancement or physical entrapment, while limited attention has been given their role in extrusion systems, particularly in relation to multiscale structural reorganization and interactions with starches of varying amylose contents. This study aimed to investigate the effects of yeast β-glucan (YG) on the physicochemical properties, multiscale structure, and in vitro digestion of extruded corn starch (ECS) prepared from corn starch (CS) with varying amylose contents: 55.79% (CS1), 32.15% (CS2), and 3.58% (CS3). YG was incorporated either before or after extrusion. The effects of YG on ECS varied depending on the amylose content of CS. Compared with ECS alone, YG addition prior to extrusion (ECS–YG) significantly reduced the hydrolysis rate and increased the content of resistant starch (RS) of ECS. This effect was particularly pronounced in ECS2–YG, which exhibited a significantly higher RS content (18.86%, P  < 0.05), and a lower estimated glycemic index than ECS2. This was likely due to the balanced amylose–amylopectin ratio in CS2, which facilitated molecular mobility and provided sufficient interaction sites for hydrogen bonding and chain entanglement with YG during extrusion. This mechanism was supported by suppressed water solubility, enhanced hydrogen bonding, increased crystallinity, improved thermal stability, and higher viscosity in ECS2–YG. These results could provide a strong basis for the application of YG in extruded corn–based starchy foods with a lower glycemic index.