Modelling of extrusion process for evaluation of spelt wholegrain snack expansion

The effect of extrusion parameters, including feed rate (15-25 kg/h), screw speed (250-750 rpm) and feed moisture (15-25%) on the expansion index of spelt wholegrain snack products was investigated. Wholegrain spelt flour was extruded using co-rotating twinscrew extruder (Bühler BTSK 30/28D, 7 sections, length/diameter ratio = 28:1, Bühler, Uzwil, Switzerland). The obtained data demonstrate that increased feed moisture leads to a decrease in the expansion of extrudates. Increasing in screw speed resulted in higher elasticity, which has resulted in the greater expansion index. The following operating conditions: screw speed (750 rpm), feed moisture (20%) and feed rate (20kg/h) provided the highest expansion index (1.93). The screw speed has the greatest positive influence on the expansion index obtained by Yoon's model.