Legume protein gelation: The mechanism behind the formation of homogeneous and fractal gels

Protein gelation can provide texture in plant-based foods and can be influenced by many factors, including protein extraction method and salt addition. However, the protein gelation mechanism is still not well understood for plant proteins, especially for isolates obtained using commercial protein extraction processes. Therefore, the structural changes that legume sources such as yellow pea, faba bean, and soybeans undergo during the gelation process to understand the differences in their gelation mechanisms was investigated herein by using small-angle neutron scattering. Among these protein sources, the commercial extraction method was found to play a major part in the gelation pathway. Intensive protein extraction methods involving isoelectric precipitation led to lower protein solubility (∼1–38% w/w), larger insoluble protein particle sizes (60–100 μm), and a gelation pathway that is dependent on the changes of the insoluble protein particles. In contrast, extraction using ultrafiltration instead of precipitation resulted in higher protein solubility (∼18–88% w/w) and smaller insoluble protein particle sizes (40–70 μm), and the structural changes observed during gelation involved the structural changes of both soluble proteins and insoluble proteins. SEM imaging also showed different gel networks, with fractal networks formed by insoluble proteins (for sources with low solubility) or more homogenous networks formed by the interactions between the soluble proteins (for sources with high solubility). Despite the differences observed in the gelation network and the protein solubility, the gelation strength exhibited by protein sources at low protein solubility were similar to the ones by protein sources at high protein solubility, demonstrating the potential of fractal gel networks in providing texture. • Protein structural changes are dependent on solvent pH and salt content. • Different gel network structures can exhibit similar gel strengths. • Less soluble protein sources form gel networks with insoluble protein particles. • More soluble protein sources form a homogeneous network around insoluble particles.