Enhancing Solubility and Reducing Thermal Aggregation in Pea Proteins through Protein Glutaminase-Mediated Deamidation

The limited solubility and stability of pea proteins hinder their utilization in liquid formulations. In this study, protein glutaminase (PG) was employed to modify pea protein isolates (PPIs) and obtain deamidated PPI with varying degrees of deamidation (DD, 10-25%). The solubility and thermal stability of these deamidated PPI samples were assessed, and a comprehensive analysis, including SDS-PAGE, zeta potential, FTIR, surface hydrophobicity, and intrinsic fluorescence, was conducted to elucidate the mechanism behind the improvement in their functional properties. The results reveal that PG modification greatly enhances the solubility and heat stability of PPI, with the most notable improvements observed at higher DD (>20%). PG modification increases the net charge of PPI, leading to the unfolding and extension of the protein structures, thus exposing more hydrophobic groups. These structural changes are particularly pronounced when DD exceeds 20%. This increased electrostatic repulsion between carboxyl groups would promote protein unfolding, enhancing interactions with water and hindering the aggregation of unfolded protein in the presence of salts at elevated temperatures (supported by high-performance size exclusion chromatography and transmission electron microscopy). Accordingly, PG-mediated deamidation shows promise in enhancing the functional properties of PPI.