Structural Characterization of Whey Protein Isolate-Soy Lecithin-Tea Polyphenols Ternary Complex and Stability of Its Emulsion Delivery System of α-Linolenic Acid

To construct an efficient emulsion delivery system for α-linolenic acid (ALA), tea polyphenols (TP), whey protein isolate (WPI), and soy lecithin (SL) were used as raw materials. The WPI-SL-TP ternary complex was synthesized by varying the mass concentration of TP (0-1.0 mg/mL), followed by the encapsulation of ALA to prepare the emulsion dilivery system. The effects of TP mass concentration on the structural and functional properties of the complex, as well as on the encapsulation efficiency and stability of the ALA emulsion were analyzed. The findings indicated that TP combined with WPI-SL through a static quenching mechanism, primarily driven by hydrophobic interactions, which facilitated the reorganization of the protein secondary structure. With the increase of TP mass concentration, the surface hydrophobicity of the complex decreased, leading to a reduction in the contact angle and an enhancement of emulsifying activity. These structural and property changes directly influenced the performance of the emulsion. The addition of TP increased the encapsulation efficiency of ALA from 65% to approximately 80%. When the TP mass concentration was lower than 0.6 mg/mL, the complex structure remained inadequately developed, resulting in aggregated emulsion droplet, increased particle size, decreased absolute Zeta potential, and reduced ALA encapsulation efficiency. When the mass concentration of TP reached 0.8 mg/mL and above, the complex exhibited enhanced electrostatic repulsion and steric hindrance due to the increased binding of TP. This interaction resulted in the formation of an emulsion characterized by smaller particle size (411.73 nm), higher absolute Zeta potential (15.93 mV), and more uniform dispersion, thereby significantly improving the encapsulation efficiency of ALA. Stability assessments indicated that the emulsion achieved optimal thermal stability at the TP mass concentration of 0.8 mg/mL. This study aimed to provide a theoretical foundation for the design of efficient delivery systems for active lipids, based on the synergistic effects of proteins, phospholipids, and polyphenols.