Physical and functional properties of wheat flour extrudates produced by nitrogen injection assisted extrusion cooking

Abstract

Extrusion cooking is widely used to produce cereal-based puffed snacks and food ingredients with superior functionality. The effects of nitrogen injection with three pressure levels (0, 100 and 200 kPa) on physical and functional properties of wheat flour extrudates were investigated in this study. The performance of nitrogen gas as a physical blowing agent and the effect of nitrogen injection pressure as a new extrusion cooking parameter were also evaluated. Nitrogen injection significantly decreased extrudate density and increased extrudate's expansion index. Nitrogen assisted extrudates had less yellow, less red but brighter color, increased crunchiness, and cold viscosity. Extrudate's water solubility increased significantly at 200 kPa nitrogen injection pressure, but no effect on water binding capacity was observed. The use of nitrogen as a physical blowing agent substantially affected all physical properties studied. The manipulation of nitrogen injection pressure as a new extrusion parameter also showed noticeable effects on water solubility and pasting properties of extrudates. Nitrogen injection during extrusion can potentially be used to produce a wider range of aerated snack foods. The manipulation of nitrogen injection pressure could be a new approach to produce more functionalized food ingredients fit for different end-products.