The role of amylose content on the structure and rheological properties of pea protein-starch systems during pressurized hydrothermal processing

Legume proteins are often subjected to hydrothermal cooking in starch containing formulations. In this work we studied the formation of structure in mixed gels containing pea protein isolate (PPI) and three maize starch types (waxy, normal-amylose and high-amylose), distinct for their amylose content (0, 26 and 56%) and swelling properties. The starch, PPI and mixed hydrogels were processed at high moisture and high temperature, and the changes in apparent viscosity were followed in situ. The amylose content in starch granules was a key parameter determining micro-structure, water partitioning and mechanical properties of the mixed gels. PPI addition to high-amylose starch (HAMS) resulted in a delay of the onset of structure formation, measured by a build-up of viscosity, and reduced gelatinization. After heating, swollen and distorted granules were present, dispersed in a protein-dominated network. In this mixed gel, along with the greater resistance to swelling during gelatinization, there was a lower extent of retrogradation, less water migration, which also reduced the hardness increase during storage, compared to the other mixtures. In the gels containing waxy and normal-amylose starch, the microstructure denoted a starch-dominated network, with protein particles segregated in the interstitial spaces of the swollen gelatinized starch. The results well describe the dynamics of interactions occurring between these biopolymers, and are an important step towards understanding the importance of their interactions during hydrothermal cooking, highlighting the relevance of phase formation during swelling.