Modification of Whey Protein Isolate with Surfactants Based on Hofmeister Series and Interaction Parameter

Developing thermoplastic materials from proteins requires structural reorganization and stabilization of specific intermolecular interactions. In this study, we modified whey protein isolate (WPI) with different surfactants─two cationic (cetylpyridinium chloride, CPC, and benzalkonium chloride, BC) and one anionic (sodium dodecyl sulfate, SDS)─to evaluate their effects on the system’s structure and thermal and rheological properties. The Hofmeister series and interaction parameters between the components were taken into consideration. Characterization was achieved by Fourier transform infrared spectroscopy (FTIR), circular dichroism (CD), dynamic light scattering (DLS), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and parallel plate rheometry. Results indicated changes induced by surfactants in the secondary conformation of proteins, particularly, the conversion of α-helical structures into β-sheets. Theoretical solubility analysis (Flory–Huggins model) predicted the miscibility for all surfactants. TGA found a greater reduction in the thermal stability. Rheological analyses showed a predominance of the elastic modulus (G′) over the viscous modulus (G″) even after thermal denaturation. Results were interpreted based on the expected interactions between the surfactants and the protein’s amino acids. Our findings suggest that modifying WPI with surfactants can be an effective strategy to tailor its structural and mechanical properties in a surfactant-dependent manner, provided that a suitable balance between protein denaturation, molecular reorganization, and thermal stability is maintained.