Starch transformation in bran-enriched extruded wheat flour

Wheat flour was extruded at different conditions of barrel temperature (120 °C and 180 °C), water content (18% and 22%) and screw speed (400 rpm and 800 rpm) with an increasing concentration of wheat bran fibers (2.8%, 12.6% and 24.4%). In the tested extrusion conditions, starch crystallites were fully dissociated. The estimated starch solubility was influenced by the process conditions and ranged from 24.1% to 63.1%. At same process conditions, the starch solubility was increased only at the highest bran level. The bran concentration influenced the glass transition temperature, melting temperature and sorption isotherm of the unprocessed wheat flour. At the extrusion conditions, it showed that higher bran levels led to a higher amount of free water and a decrease in starch glass transition temperature of up to 13 K. The differences in starch transformation, induced by the concentration of bran, might contribute to the modulation of the expansion properties of bran-containing starchy foams.