Influence of germination and extrusion with CO2 injection on physicochemical properties of wheat extrudates

Whole wheat and germinated wheat flour were extruded in a laboratory co-rotating twin screw extruder with die temperatures (90 and 130 °C), screw speeds (150 and 200 rpm) and CO2 injection. The effects of germination and extrusion process on specific mechanical energy (SME) input, expansion ratio, specific length, piece density, elastic modulus, breaking strength, colour, water solubility index (WSI), water absorption index (WAI) and microstructure were determined. The study showed that the use of germinated wheat flour increased the specific length, lightness and the WSI. When CO2 was injected, the expansion ratios (only 90 °C die temperature for extruded germinated wheat) and lightness were significantly increased (p < 0.05). The chemical properties (crude protein, fat, ash, reducing sugar, γ-aminobutyric acid, soluble arabinoxylans, β-glucan and phytic acid) were also investigated. The germination step and extrusion process mainly affected the chemical properties. However, the difference of die temperatures, screw speed and CO2 injection had slight effect on the chemical properties.