Maillard Reaction Modification of Walnut Gluten Antioxidant Peptides: Process Optimization, Conformational Rearrangement, and Flavor Formation

To improve the flavor quality and antioxidant activity of walnut gluten peptides, gluten was extracted from defatted walnut meal by alkaline solubilization and acid precipitation, hydrolyzed with alkaline protease to prepare antioxidant peptides, and further modified by the Maillard reaction. The optimal sugar source was selected by single-factor experiments, and reaction conditions were optimized by response surface methodology. Peptide conformational changes were characterized by UV, fluorescence, DSC, FTIR, and SEM, while changes in amino acid composition, flavor properties, and antioxidant activity were systematically evaluated. Fructose was identified as the optimal sugar source. The optimal reaction conditions were a peptide-to-sugar ratio of 1:1.2, 78.5 °C, initial pH 7.6, and 2 h reaction time, under which the sensory score reached 8.5 and DPPH radical scavenging activity reached 66.92%. Maillard modification markedly altered peptide conformation, as shown by increased UV absorbance, decreased intrinsic fluorescence intensity with a red shift, an increase in denaturation temperature from 80 °C to 100 °C, reduced α-helix content, increased β-sheet content, and transformation of the microstructure from a loose porous morphology to dense block-like aggregates. Free amino acid content increased initially and then decreased, whereas total essential amino acids were largely retained, indicating that the overall nutritional composition was preserved. However, further evaluation of digestibility and bioavailability is required to confirm nutritional value. These findings provide a feasible strategy for improving the flavor and functional properties of walnut gluten peptides and support their high-value utilization.