Heating and neutralization significantly impact pH-shifting treatment: A case study on oat protein isolate

Oat globulin protein is known for its poor solubility at neutral pH due to its compact structure. Recent studies show that combining alkaline treatment with pH shifting can alter protein functionalities, such as solubility. However, the impact of specific processing conditions, such as heating and neutralization, requires further investigation. Using oat protein isolate (OPI) as an example, the study evaluated different heating temperatures at pH 12 and compared neutralization with HCl and citric acid on OPI solubility. Results showed that simple pH shifting (from pH 7 to 12 to 7) did not improve solubility, but integrating heating (100 °C, 30 min) with citric acid neutralization significantly enhanced and maintained OPI solubility at neutral pH (70-75 %). This finding was supported by physicochemical characterizations, including nanoscale particle size, loss of thermal denaturation peak, formation of 2-10 kDa peptides, and reduced β-sheet content with increased random coil structures. Furthermore, citric acid, compared to HCl, combined with heating at pH 12, maintained a higher zeta potential, resulting in improved OPI stability for up to seven days. These results provide valuable insights into the role of non-enzymatic processing methods in modifying plant protein solubility and its potential applications in food formulations.