Physical and hydration properties of expanded extrudates from a blue corn, yellow pea and oat bran blend

- A blend of blue corn, yellow pea and oat bran was extruded in a twin-screw extruder.
- Specific mechanical energy was inversely correlated to feed moisture content.
- Selected physical and functional properties were evaluated.
- Optimization for a few key variables was possible.

Extrudates were prepared from a blue corn, yellow pea and oat bran blend employing a twin-screw extruder. Response surface methodology was used to evaluate the effect of extrusion-cooking process independent variables: screw speed (SS, 300-400 rpm), die temperature (DT, 120-160 °C) and feed moisture content (FMC, 20-25%) on the system parameters (specific mechanical energy and product temperature), physical properties (sectional and specific longitudinal expansion indices, porosity, hardness and color attributes), hydration properties (water absorption and solubility indices, and pasting properties), microstructure and x-ray diffraction. Although, system parameters, physical and hydration properties were affected by SS and DT, the greatest effect was due to the FMC. Indicating this way lubricant effect as the preponderant factor controlling extrusion effects on raw material. Decreased FMC increased specific mechanical energy, expansion, soluble compounds; and decreased hardness, time to raw peak viscosity, raw peak, total setback and final viscosities. Data were also analyzed with a principal component analysis, showing that 74.67% of data variability can be explained defining two components corresponding to the 62.10% that was due to mechanical effect and 12.57% that was related to thermic effect. Conditions obtained for multiple optimization were: 158.64 °C, 371.98 rpm, 18.38% FMC.