Development of zein-based complexes and conjugates with enhanced surface hydrophilicity: Structure, emulsifying, foaming, and antioxidant properties

Corn zein is an abundant and inexpensive source of plant proteins. However, it is a strongly hydrophobic molecule with poor water solubility, which limits its range of applications in the food and other industries. In this study, zein-EGCG-alginate ternary conjugates were prepared using an alkaline treatment combined with the Maillard reaction. The nature of the conjugates formed was characterized using a range of analytical methods, including SDS-PAGE, dynamic light scattering, particle electrophoresis, spectroscopy, calorimetry, and electron microscopy. Scanning and transmission electron microscopy showed that the particles in the dispersion of ternary complexes were larger and more irregularly shaped than those in the original protein dispersion. Spectroscopic analyses indicated alterations in the structure of the proteins caused by both the alkaline and Maillard reaction treatments. Ternary conjugates (zein-EGCG-alginate) had better emulsification and foaming properties than single proteins (zein) or binary conjugates (zein-EGCG). Moreover, the surface hydrophobicity of the ternary complexes was lower, while their thermal stability and antioxidant activity were higher. For instance, the DPPH and ABTS free radical scavenging activity of the ternary conjugates were enhanced to around 67% and 89%, respectively. The alkaline-Maillard treatment also greatly improved the water dispersibility of zein, reaching a solubility level close to 60%. This study may broaden the range of applications of zein as a functional ingredient in the food and other sectors.