Process optimization for yam flour incorporated in expanded extrudates

Abstract

The effects of incorporation of water yam (Dioscorea alata L.), feed moisture content, and extrusion conditions on physical characteristics of expanded extrudate were studied using response surface methodology. The mixture was prepared using maize grit, rice grit, and gram flour. Yam flour was incorporated at 10–20% level in the feed mix, and the moisture content of the feed was varied from 13% to 15%. The extrusion process was run at varied temperature conditions (90–110°C) in a single screw extruder. A numerical multi-response optimization technique was used for optimizing input variables. Lateral expansion (LE) and starch digestibility had significant (p < 0.05) positive effects due to yam incorporation, while density, water absorption index (WAI), and water solubility index (WSI) had a significantly negative effects. Feed moisture had a significant (p < 0.05) effects on product density and WSI positively. Barrel temperature had a significant (p < 0.05) positive effects on LE and starch digestibility where density and WAI had a significant negative effects. Optimum operating conditions for yam flour addition, feed moisture and barrel temperature were 20%, 13.28%, and 108.83°C, respectively. Corresponding to these process variable, predicted values were 144.65% for LE, 0.222g/cm3 for density, 6.002 g/g for WAI, 7.217% for WSI, and 305.15 µg/g for maltose content with desirability 0.848. The extrusion conditions and response variables reveal the possibility of using yam to produce extruded expanded snacks.

Keywords

• single screw extrusion
• response surface methodology
• rice grit–maize grit–gram flour–yam flour
• physical characteristics