Molecular weight as a key determinant in the covalent complexation of walnut peptides and phenolic acids: a combined analysis of binding effects, structural properties, and antioxidant activities.

The extent of polyphenol binding directly determines the enhancement of peptide bioactivity, yet the influence of peptide molecular weight on this interaction remains poorly understood. Our results show that small molecular weight walnut peptides (S-WP) exhibit higher phenolic acid binding ratios and more pronounced reductions in free amino and sulfhydryl groups, suggesting a greater propensity to form covalent conjugates. Structural characterization indicates that covalent conjugation reduces peptide surface hydrophobicity, enhances ultraviolet absorption, induces fluorescence quenching, and increases random coil content. Antioxidant evaluations further confirm that phenolic acid conjugation significantly enhances the antioxidant activity of walnut peptides, with effectiveness positively correlated with phenolic acid content. Overall, this study provides the first evidence of the pivotal role of peptide molecular weight in conjugate formation, offering a novel strategy for developing functional walnut peptide-phenolic ingredient systems.