Effect of pH-shifting combined with ultrasound treatment on the physicochemical, structural, and gelation properties of oxidized pea protein isolate

Oxidized pea protein isolate (OPPI) exhibits reduced solubility and impaired functional properties, limiting its application in food systems. This study aimed to modify the physicochemical and structural characteristics of OPPI using either pH-shifting alone or pH-shifting combined with sonication for enhancing its gelation properties. These treatments significantly promoted protein unfolding, reducing the aggregate size (from 1303 to 178 nm) and increasing protein solubility (from 5.8 to 23.2%), surface hydrophobicity (1.8-fold), and free sulfhydryl content (from 0.62 to 1.09 μmol/g). Only OPPI treated with both pH-shifting and sonication formed transglutaminase-induced gels. The gelation properties were pH-dependent, with higher pH values yielding stronger gels, as evidenced by increased shear modulus and hardness. This enhancement may result from greater exposure of active sites on protein surfaces at elevated pH, which promotes intermolecular interactions and enzymatic cross-linking. Thus, combining pH-shifting and ultrasonication methods is an effective strategy for enhancing the gelation properties of OPPI.