Protein rich extruded products prepared from soy protein isolate-corn flour blends

Protein rich extruded products were prepared from soy protein isolate and corn flour blends using a twin screw extruder and the physical properties of the extruded product were evaluated and related to process variables: soy protein isolate (SPI) (32.2-66.6 g protein/100 dry matter), feed moisture (31.6-48.4 g/100 g) and process temperature (126.4-193.6 °C). A central composite rotate design (CCRD) and response surface methodology was used to evaluate the significance of independent and interaction effects of extrusion process variables on the product's various physical properties (breaking stress, bulk density, expansion ratio, water solubility index, rehydration rate and color). Second order polynomial regression equations were developed to relate the product responses to process variables as well as to obtain the response surfaces plots. The independent variables had significant (p ≤ 0.05) effects on physical properties of extrudates: (i) higher SPI and feed moisture contents increased the breaking stress and bulk density, but decreased the expansion ratio, water solubility index, and rehydration rate, (ii) higher SPI content decreased the color L value, whereas higher feed moisture content increased it, (iii) higher temperatures increased breaking stress, expansion ratio, rehydration rate and L value, but decreased the bulk density and water solubility index. © 2012 Elsevier Ltd.