In vitro protein digestibility and content of thiamin and riboflavin in extruded tarhana, a traditional Turkish cereal food

Tarhana, a traditional Turkish yogurt-wheat flour mixture, was extruded using a twin-screw extruder. The effects of extrusion variables and post-extrusion process on the in vitro digestibility (PD) of the protein and contents of thiamin and riboflavin in the extruded samples were measured and the results were compared with those of an unextruded control sample. The changes in barrel temperature (60–120°C), feed rate (10–20 kg/h, wb) and screw speed (10–300 rpm) did not have any significant (p > 0.05) detrimental effect on the PD and thiamin and riboflavin contents of tarhana at constant moisture content (43%, wb). However, oven-drying at 55 °C for 48 h after extrusion caused approximately 30% thiamin losses in the samples while the in vitro protein digestibility and riboflavin content of the samples did not change significantly (p > 0.05).