Extrusion of pea snack foods and control of biopolymer changes aided by rheology and simulation

Abstract

Pea flour and a blend of pea starch and protein isolate with a starch-to-protein ratio close to 2/1 were processed using co-rotating twin-screw extruders. Different extruder scales operated at a moisture content of 18–35% and a screw speed of 120–700 rpm resulted in large intervals of melt temperature T (95–165 °C) and specific mechanical energy SME (150–2000 kJ/kg). With increasing T and SME, starch solubility in water increased due to starch melting and depolymerisation, and protein solubility in SDS decreased due to formation of protein aggregates linked by disulphide bonds. Extruded foods’ morphology was studied by CLSM. Protein cross-linking increased the median size of protein aggregates; starch destructuration increased the area of the starch phase to the detriment of the protein one. Melt shear viscosity was determined using a pre-shearing capillary rheometer. The melts exhibited shear-thinning behaviour according to a power-law model, with values close to those of model parameters observed for pea flour and SP 2/1 blend. The rheological model was implemented in a 1D global extrusion model to simulate pea ingredient extrusion. Satisfactory correlations between predicted extrusion variables (T, SME) and biopolymer transformation suggested that products with target structure can be obtained using simulation to tune extrusion conditions.