Optimisation of extrusion process to transform hardened chickpeas (Cicer arietinum L) into a useful product

The objective of this work was to determine the optimum conditions for the production of extruded flour from hardened chickpeas (Cicer arietinum L). Hardened chickpeas were produced using accelerated storage at 33-35°C and 76% relative humidity for 160 days. Hardened chickpeas were broken, dehulled and softened with a salt solution (2.5 g l^-1 NaCl+7.5 g l^-1 NaHCO₃ in distilled water) prior to extrusion. The single-screw extruder operation conditions were selected from factorial combinations of process variables: extrusion temperature (ET, 130-160°C), feed moisture content (FMC, 200-300 g H₂O kg^-1, wet basis) and screw velocity (SV, 150-200 rpm). Response surface methodology was applied as optimisation technique over four response variables: in vitro protein digestibility (PD), total colour difference (ΔE), water absorption index (WAI) and water solubility index (WSI). Predictive models for response variables were developed as a function of process variables. The conventional graphical method was applied to obtain maximum PD and WAI and minimum ΔE and WSI. Contour plots of each of the response variables were utilised, applying superposition surface methodology to obtain three contour plots for observation and selection of the best (optimum) combination of ET (150.5°C), FMC (265 g H₂O kg^-1) and SV (190.5 rpm) for the production of extruded flour from hardened chickpeas with a single-screw extruder. Extrusion significantly improved the in vitro protein digestibility (21.7%) and protein efficiency ratio (36.9%) of hardened chickpeas.