Molecular Interplay Between Plant Proteins and Polyphenols: pH as a Switch for Structural and Functional Assembly

Understanding how plant proteins interact with polyphenols under different pH conditions is key to unlocking the full functional potential of natural ingredients in food systems. This study investigates the pH-dependent binding mechanisms and structural transformations of three underutilized plant proteins: mustard protein concentrate (MP), primrose protein meal (PP), and sunflower meal protein isolate (SMP) in complexation with red cabbage polyphenols (RC) using spectroscopic and microscopic techniques, we show that alkaline conditions (pH 7-9) enhance anthocyanin binding, driven by hydrogen bonding and hydrophobic interactions, particularly in PP and SMP. However, this increased binding is accompanied by greater protein unfolding and aggregation, which affects solubility and colloidal behavior. PP9 demonstrated the strongest antioxidant activity, while MP3 retained anthocyanin stability in acidic conditions. Emulsification and foaming properties varied across proteins and pH: PP showed the highest emulsification at acidic pH, MP had superior emulsion stability at alkaline pH, and SMP maintained performance across all conditions. CLSM imaging confirmed that SMP-based emulsions were the most structurally stable. These findings provide molecular insight into how pH governs the assembly, stability, and functionality of protein-polyphenol complexes, paving the way for the rational design of next-generation plant-based food formulations.