Effect of different structures of β-glucan on extruded starch: physicochemical properties, multiscale structure, and in vitro digestibility

Yeast and oat β-glucans differently influence extruded corn starch structure. • Yeast β-glucan addition before extrusion increases structural ordering. • Yeast β-glucan addition before extrusion promotes higher resistant starch formation. • Systems containing yeast β-glucan show relatively lower starch digestibility. • Yeast β-glucan is associated with a lower estimated glycemic index. Yeast β-glucan and oat β-glucan exhibit distinct molecular architectures that may differently regulate starch structure and digestibility during food processing. This study aimed to compare the effects of these two β-glucans incorporated before and after extrusion on the physicochemical properties, multiscale structure, and in vitro digestibility of extruded corn starch. Extrusion significantly decreased the relative crystallinity of corn starch and transformed its crystalline structure to a V -type pattern. Incorporation of β-glucans before extrusion led to more pronounced interactions between starch and β-glucan molecules than post-extrusion addition. Samples containing yeast β-glucan exhibited lower water solubility, higher short-range ordered structure, and higher relative crystallinity values than those containing oat β-glucan, indicating the formation of a more rigid structure. Moreover, the findings on rheology and pasting properties showed that the former system had higher viscosity than the latter, further confirming stronger structural reinforcement in systems incorporating yeast β-glucan before extrusion. Finally, the starch system containing yeast β-glucan exhibited a higher resistant starch content (32.09%) and lower estimated glycemic index (83.80 ± 0.11) compared with those containing oat β-glucan (28.34%, 84.96 ± 0.21), indicating greater digestion resistance. These results suggest that the molecular architecture of β-glucans and their timing of incorporation may influence the structural organization and digestion behavior of extruded starch systems. Download: Download high-res image (236KB) Download: Download full-size image