pH cycling-induced structural remodeling of walnut protein-whey protein isolate complex: Trade-off between digestibility and bioactivity

The bioactivity of plant proteins is often limited by the compact and aggregated structures. In this study, the walnut protein-whey protein isolate (WP-WPIp) complex was constructed via pH cycling. This treatment appeared to induce conformational changes characterized by a disordering of secondary structures and a disruption of tertiary folds, which may have exposed hydrophobic residues and reduced steric hindrance. Structural remodeling enhanced digestibility, with the complex reaching a hydrolysis degree of 78.78% versus 73.12% for native WP, likely facilitating enzymatic accessibility. Bioactivity assessments revealed a structure-dependent trade-off. Antioxidant capacity (DPPH and ABTS) and xanthine oxidase inhibition (up to 35.09% gastric phase) were synergistically enhanced whereas sodium taurocholate binding and cholesterol esterase inhibition decreased, likely due to reduced surface hydrophobicity. Digestion products also showed moderate α-amylase and α-glucosidase inhibition. This study elucidates the complex interplay between conformation and multifunctionality providing insights for high-value plant protein utilization through precision structural design.