Effect of pH on the Formation, Disintegration and Antioxidant Activity of Mung Bean Protein Fibrils

Protein fibrils are highly ordered structures. Mung bean protein (MBP) fibrils were fabricated after heating under acidic condition. The formation mechanism, structural variety and antioxidant capacities of mung bean protein fibrils were investigated under different pH conditions. The fibrillation process was characterized by extensive hydrolysis of MBP into low-molecular-weight peptides, which subsequently self-assembled into fibrils with increasing contour length over time. The formed fibrils exhibited a dominant β-sheet structure but demonstrated high sensitivity to pH changes. Upon adjustment to pH 7.0, the fibrils changed into amorphous aggregates, accompanied by a structural transition to random coils. Pretreatment of MBP with neutral protease and chymotrypsin yielded hydrolysates with distinct peptide profiles, leading to the formation of fibrils with varied morphologies upon acidic heating. Furthermore, the antioxidant activity of MBP and its fibrillar aggregates was highly dependent on pH and structural state. While fibril formation at pH 2.0 led to a reduction in radical scavenging activity of MBP, the subsequent pH-shifted aggregates at pH 7.0 resulted in a significant enhancement of antioxidant capacity. These findings provide fundamental insights into the formation, stability, and bioactive properties of MBP fibrils, emphasizing their pH-dependent behavior.