Impact of protein content on physical and microstructural properties of extruded rice starch-pea protein snacks

The physical and microstructural properties of pea protein-fortified, expanded snacks were examined after extrusion at various moisture contents, temperatures, screw speeds and pea protein isolate (PPI) contents of up to 50% (w/w). The highest expansion and, thus, the lowest bulk density and hardness were recorded at a PPI content of 10% (w/w). An increase of extruder screw speed from 400 to 600 rpm resulted in enhanced expansion of extrudates, while increasing die temperature (from 130 to 150 °C) or moisture content (from 23 to 26%) did not significantly change expansion of different extruded blends. X-ray micro-computed tomography images indicated internal structural differences between extruded blends. Most prominent was the non-uniform structure of extrudates with a PPI content of 30% (w/w). This can be attributed to the decreased glass transition temperature as result of increasing PPI content resulting in delayed material solidification after exiting the extruder die. Extrudates with a PPI content of 50% (w/w) showed poor expansion and were significantly (p < 0.05) harder than extrudates with lower PPI contents.