Extrusion of tarhana: effect of operating variables on starch gelatinization

Tarhana, a traditional Turkish cereal food, was extruded using a twin-screw extruder. The effect of barrel temperature (6–120 °C), feed rate (10–20 kg h−1, wet basis) and screw speed (100–300 rpm) on starch gelatinization was investigated using response surface methodology at constant moisture content (43%, wet basis). A regression equation for predicting starch gelatinization was developed. Barrel temperature had the most pronounced effect on starch gelatinization at constant moisture content, followed by feed rate and screw speed. Response surface plots suggest that a high degree of starch gelatinization can be achieved when tarhana is extruded at high barrel temperatures and screw speeds but low feed rates (i.e. high residence times).