Influence of extrusion-cooking on the physico-chemical properties of wheat bran

Wheat bran was extruded under various conditions with a Clextral BC 45 twin screw extruder. Water (6·1–17·5 % of dry solid feed rate) and feed rate (20–32 kg/h) were varied in order to obtain treatments of different severities. These were monitored by the specific mechanical energy measured by the electrical consumption of the main motor drive. The water solubility of the extruded products increased from 20 to 40 % and the soluble fibre content from 8 to 16 %. These values were well correlated to the specific mechanical energy (230–380 kWh/t). Analysis of the sugar composition showed a slight increase in the solubility of glucuronoarabinoxylans arising from the external pericarp layer and a marked increase in the solubility of arabinoxylans and β-glucans probably arising from the aleurone and endosperm cell walls. Water absorption capacity, as measured by the Baumann method, increased from 270 to 375 % for the products processed under low severity treatments.