Response surface methodology for evaluation of physical and functional properties of extruded snack foods developed from food-by-products

Response surface methodology was used to investigate the effects of extrusion conditions including moisture content (12–18%), temperature (150–175 °C), screw speed (200–280 rpm), and change in feed composition, durum clear flour (8–20%), partially defatted hazelnut flour (PDHF) (5–15%) and fruit waste (3–7%) contents on the physical and functional characteristics of the extruded snack food based on rice grit in combination with fruit waste, durum clear flour and PDHF. Response variables are bulk density, porosity, water absorption and water solubility indices and sensory properties of the extruded snacks. The product responses were most affected by changes in PDHF content and to a lesser extent by fruit waste content. Increasing PDHF content caused increase in bulk density and water solubility index, but decrease in porosity and water absorption index of the extruded snacks. Changing process conditions affected the physical and functional properties of produced snacks. The sensory evaluation of extrudates suggests that extrusion of PDHF, fruit waste and durum clear flour in combination with rice grit can produce acceptable extruded snack.