Fabrication, characterization, and emulsifying ability evaluation of flexible zein-sodium caseinate complexes

To comprehensively enhance the physicochemical properties of zein nanoparticles and the performance of emulsions, a dual-modification strategy was employed. This involved pretreating zein with acid or alkali to obtain modified zein, followed by complexation of native or pretreated zein with various concentrations of sodium caseinate (CS) via an anti-solvent method. Dual modification markedly altered the particle size of zein nanoparticles. Among the single modification methods, alkali-modified zein (Azein) showed the smallest particle size. Of all the dually modified binary complexes, Azein-2% CS exhibited the smallest particle size and the highest absolute zeta potential value. X-Ray Diffraction (XRD) results revealed structural differences between singly and dually modified zein, with the Azein-CS complex exhibiting an amorphous structure and improved thermal stability. Fourier transform infrared spectroscopy (FTIR) confirmed that electrostatic interactions and hydrogen bonding are the main driving forces for complex formation. The dually modified Azein-2% CS complex demonstrated the highest emulsifying activity index (EAI) and emulsion stability index (ESI), and formed Pickering emulsions with the smallest average droplet size and a uniform size distribution. This study provides a solid theoretical foundation for broadening the application scope of zein and offers an effective strategy for designing functional particles with strong potential for food-grade applications.