Interactions of Plant Protein and Natural Colorant: A Structural and Functional Relationship of Broccoli Protein and Marigold Color Compounds

ABSTRACT Broccoli flower proteins (BFPs) are a sustainable alternative plant protein source; however, their application in food systems remains limited because of poor techno‐functional properties compared with conventional proteins. This study employed a clean‐label strategy to improve BFP functionality using marigold color extract (MCE), a phytochemical‐rich floral waste product. BFP–MCE complexes were prepared using different extract concentrations (0%–4%, v/v) and characterized through Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and functional property analysis. FTIR analysis revealed concentration‐dependent structural modifications, with α‐helix content decreasing from 50.3% to 28.4%, while β‐sheet structures increased from 22.1% to 34.2% following MCE incorporation. SEM observations revealed a transition from porous protein aggregates to dense, cohesive network structures. Structural changes significantly improved protein functionality, including increased foaming capacity from 14.9% to 69.2%, foam stability from 6.1% to 42.0%, emulsifying activity index from 23.1 to 76.2 m 2 /g, and antioxidant activity from 41.2% to 65.3%. Surface hydrophobicity decreased from 19.3 to 10.2 a.u., indicating improved protein–water interactions. Metabolomic profiling of MCE identified flavonoids, phenolic acids, amino alcohols, oxygenated heterocycles, and sesquiterpenes as major compounds that are potentially responsible for noncovalent interactions with proteins via hydrogen bonding, hydrophobic interactions, π–π stacking, and electrostatic attraction. This research shows that MCE successfully modified BFPs into sustainable plant protein ingredients with improved functionality and enhanced antioxidant activity for clean‐label food production.