Effect of hydrophilic and lipophilic compounds on zein microstructures

Zein, the prolamine of corn, contains nearly an equal amount of hydrophilic and lipophilic amino acid residues. Its tertiary structure has a regular geometry measuring 17x4.5x1.2 nm. The structure of zein allows it to function as a polymeric amphiphile. Zein had been observed to self-assemble into periodic bilayer structures and nanotubes. This work investigated the structural development of zein self-assemblies as affected by the hydrophilic-lipophilic balance (HLB) of the system. The formation of several structures, including spheres, sponge, and lamellae, were identified. Images were obtained by SEM, AFM, and FIB/SEM. The radius of curvature of the observed assemblies was affected by the HLB of the components in the system. Thus, lipophilic flavor oils increased the curvature of zein spheres producing smaller spheres. Curvature decreased in the presence of amphiphilic fatty acids forming sponges with interconnected channels. Hydrophilic compounds decreased the curvature to the point of forming smooth films. The results of this study see a future in microencapsulation and controlled release systems for flavor and bioactive compounds in the food industry.