Heat-induced structural modulation of lupin protein: Enhancing protein functionality and anthocyanin stability...

Lupin protein, a plant protein with promising nutritional and functional properties, has potential for stabilizing anthocyanins (ACN) in acidic beverage systems. In this study, lupin protein was thermally modified at 50, 60, 70, and 80 °C to investigate how heat-induced structural changes influence protein-ACN interactions, ACN stability, and protein digestive behavior. Thermal treatment significantly increased protein surface hydrophobicity and decreased solubility, accompanied by secondary structural rearrangements, including reduced α-helix content and increased β-sheet formation. These structural changes promoted protein-ACN interactions, which were predominantly governed by static quenching and hydrophobic interactions. Thermally treated proteins exhibited improved protection against ACN degradation during thermal processing, with ACN degradation after heating at 80 °C for 2 h decreasing from 31.55% in the native protein system to 25.35% in the H80 system. Storage stability was also enhanced, as the ACN degradation rate constant decreased from 0.04 d^-1 in NP, H50, and H60 systems to 0.02 d^-1 in H70 and H80 systems, while the half-life increased from approximately 16 days to 34-35 days. In vitro digestion showed that thermal treatment slightly increased gastric protein hydrolysis, whereas ACN complexation markedly reduced hydrolysis, suggesting reduced enzyme accessibility associated with protein-ACN interactions. Notably, thermally treated protein-ACN complexes maintained higher hydrolysis than native protein-ACN complexes, indicating a balance between heat-induced structural loosening and ACN-induced steric shielding. Overall, controlled thermal treatment effectively regulated lupin protein structure and hydrophobicity, enhanced ACN stability, and modified protein digestive behavior, providing useful insights for the design of plant protein-polyphenol systems in acidic functional beverages.