Low moisture extrusion of pea protein and pea fibre fortified rice starch blends

Low moisture extrusion of rice starch fortified with pea protein and pea fibre was investigated as a potential approach to meet the increasing demand for novel food products with a balanced nutritional profile. Blends with four different protein contents (0, 10, 25 and 42% d.b.) and four different fibre contents (0, 8, 16 and 24%d.b.) were extruded. A full factorial design was applied for the blend composition, resulting in the investigation of 16 different blends. Screw speed (400 and 600 rpm), die temperature (130 and 150 °C) and moisture content (23 and 26%) were varied to identify their influence on the expansion behaviour and microstructure of the extrudates. Significant effects of both blend composition and extrusion conditions on the product characteristics were observed. The addition of protein and fibre resulted in increased specific mechanical energy inputs, bulk densities as well as air cell densities. At intermediate protein and fibre contents, expansion of the extrudate was statistically significant increased compared to the pure rice starch. However, the lowest expansion was observed for the highest protein and fibre content. Scanning electron microscopy, light microscopy and X-ray micro-computed tomography were used to identify microstructural changes caused by protein and fibre fortification. Microstructural analyses revealed that at the highest protein contents (42%), protein and starch were distributed in thin layers within the extrudate which is proposed to cause the decreased sectional expansion indices.