Functional effects of xanthan gum on quality attributes and microstructure of extruded sorghum-wheat composite dough and bread

This study was performed in order to enhance the extruded sorghum-wheat composite dough (SWCD) and bread (SWCB) quality using xanthan gum. In order to investigate the effect of extrusion cooking, extruded (at 10% feed moisture and 160 °C die temperature) and non-extruded sorghum flours were separately substituted with wheat flour at 10:90 sorghum/wheat ratio. In addition, to improve the quality of the final product, xanthan gum (0.5 and 1%) was added during the mixing of doughs ingredients. Results revealed that unlike non-extruded SWCD, addition of xanthan gum to extruded SWCD decreased the dough strength. SEM observation demonstrated that composite dough containing either extruded or non-extruded sorghum had similar structures. On the other hand, in contrast to extruded SWCD, xanthan gum incorporation to non-extruded SWCD formed a uniform structure. Extruded SWCD had less viscous and more solid-like characteristics than the non-extruded SWCD. The elasticity and solidity of both doughs containing extruded and non-extruded sorghum increased with the addition of xanthan gum. In general, it was found that extruded SWCD had the highest (10.75 °C/min) and non-extruded SWCD containing 0.5% xanthan gum had the lowest (7.33 °C/min) heating rates. The crumb cell structure also showed that the addition of xanthan gum increased the average pore size and decreased the number of cells/cm2, total area and pore area fraction (%) of crumb in the extruded SWCB. Bread crumb hardness increased when extruded sorghum flour and xanthan gum were used.