Effects of 2,2′-Azobis(2-amidinopropane) dihydrochloride (AAPH) on Functional Properties and Structure of Winged Bean Protein

Background: The impact and regulation of protein oxidative modification on protein functional properties is a research hotspot in food processing. This study aimed to clarify the mechanism of free radical oxidation on the structure and function of winged bean protein. Methods: Winged bean protein was treated with different concentrations of AAPH (0.04 mmol/L, 0.20 mmol/L, 1.00 mmol/L). The functional properties (solubility, surface hydrophobicity, zeta potential), oxidation degree indicators, and secondary and tertiary structures of winged bean protein were tested and characterized under different oxidation conditions. Results: Low-concentration (0.04 mmol/L) AAPH led to the decomposition of winged bean protein, with decreased particle size and increased surface hydrophobicity and solubility; medium-concentration (0.20 mmol/L) AAPH caused significant aggregation of winged bean protein, with decreased surface hydrophobicity and solubility; high-concentration (1.00 mmol/L) AAPH led to the rearrangement of winged bean protein aggregates, forming more soluble aggregates and increasing solubility. With the gradual increase in AAPH addition, the α-helix and random coil structures of winged bean protein showed a trend of first increasing and then decreasing, while the β-sheet structure showed a trend of first decreasing and then increasing, and the β-turn structure remained almost unchanged. Conclusions: Under mild oxidation conditions (AAPH = 0.04 mmol/L), the functional properties of winged bean protein could be optimized. However, under relatively strong oxidation conditions (AAPH > 0.20 mmol/L), the structural integrity and functionality of winged bean protein would be compromised. This study helps deepen our understanding of the oxidative modification mechanism of winged bean protein.