Effect of Incorporation of Various Food By-products on Some Nutritional Properties of Rice-based Extruded Foods

Various food by-products were incorporated into rice grits and submitted to extrusion cooking to produce fortified extruded food products. The blends of various formulations of durum clear flour (820%), partially defatted hazelnut flour (PDHF) (515%), fruit waste blend (37%) and rice grits were extruded using single screw extruder. Response surface methodology was used to evaluate the effects of process variables, namely the feed moisture content (1218%), barrel temperature (150175 C) and screw speed (200280 rpm), and change in feed composition on total phenolic content, antioxidant activity, percent starch gelatinization and starch digestibility of the extrudates. Extrusion cooking process significantly increased the level of phenolic compounds and starch digestibility of extruded products. Increasing PDHF and fruit waste content caused increase in total phenolic content and antioxidant activity of the extruded samples, whereas percent starch gelatinization and digestibility values decreased. Moisture content and temperature significantly influenced the total phenolic content, antioxidant activity, percent starch gelatinization and starch digestibility values. In extruded samples, positive correlations were determined between antioxidant activity and total phenolic matter and percent starch gelatinization and the starch digestibility values, respectively. Key Words: partially defatted hazelnut flour, fruit waste, extrusion, starch digestibility, phenolic conten