Acidic environment-mediated interactions between Antarctic krill protein amyloid fibrils and catechins: Structural modulation and functional response

Interactions between proteins and polyphenolic compounds are essential for modulating both structural integrity and functional behavior within acidic food matrices. However, existing studies have focused on globular proteins under neutral conditions, leaving protein-polyphenol interactions in acidic environments insufficiently understood. In this study, Antarctic krill protein amyloid fibrils (AF) were employed as a model system to systematically investigate their interactions under acidic conditions with structurally distinct catechins, including epicatechin (EC), epigallocatechin (EGC), epicatechin gallate (ECG), and epigallocatechin gallate (EGCG). The results indicated that catechins formed stable complexes with AF, which caused pronounced alterations in particle size, surface charge, and microstructural morphology. Esterified catechins, particularly EGCG, exhibited enhanced binding strength and induced more substantial modifications compared with non-esterified counterparts. Spectroscopic and thermodynamic analyses revealed that the association between AF and catechins was dominated by non-covalent interactions and proceeded as a spontaneous and exothermic binding process. These interactions induced β-sheet structure rearrangement and accelerated the shift from ordered fibrillar assemblies to more disordered aggregates under acidic conditions. At the cellular level, AF-catechin complexes exhibited good biocompatibility and effectively alleviated H 2 O 2 -induced oxidative stress. Overall, this study elucidates the structure-dependent interaction mechanisms between protein amyloid fibrils and polyphenols, providing a theoretical basis for the design of protein-polyphenol composite systems in acidic functional food applications.