Deciphering the mechanism underlying poor aqueous solubility of extracted quinoa proteins

This study aimed to decipher the mechanisms underlying poor solubility of quinoa proteins by investigating the form of quinoa proteins dispersed in water and how protein-protein interactions influenced the kinetic stability of proteins in the dispersions. Specifically, the relative solubility and the forms of quinoa proteins in 1-5 w/w% protein dispersions were determined by separating proteins via centrifugation and/or ultrafiltration. The kinetic stability of quinoa proteins in the supernatants over a 3-week storage period was characterized by determining the changes of concentration, composition and physicochemical properties of quinoa proteins and predicting protein-protein interactions. The results showed that quinoa proteins existed mainly as differently-sized protein aggregates in the dispersions, leading to low relative solubility. The coagulation of protein aggregates in the supernatants caused severe precipitation during the first week of storage whereas they were disassociated simultaneously. With further storage, the remaining proteins in the supernatants reached kinetic stability, which was contributed by stronger electrostatic repulsion and lower surface hydrophobicity. Moreover, 11S globulin and 2S albumin were precipitated and solubilized together during storage, which was ascribed to intermolecular interactions driven by multiple sites between 11S globulin and/or 2S albumin. This study lays a foundation for extensive utilization of quinoa proteins.