Insights into the complex coacervation behavior and interaction mechanism of nisin and rhamnolipid

Nisin is a natural, safe and highly effective food preservative that can inhibit the growth and reproduction of most gram-positive bacteria. However, the antimicrobial effect of nisin shows poor stability, which is a disadvantage in practical applications. Microencapsulation of nisin through complex coacervation addresses its poor antibacterial stability and limited spectrum. This study investigated the phase behavior, microstructural properties, and interaction mechanisms between nisin and rhamnolipid (RL).

The results showed that the characteristic boundary pH values (pH_c, pH_φ1, pH_opt, pH_φ2) of the nisin/RL complex coacervates increased significantly by decreasing the RL to nisin mass ratio from 1:12 to 1:16 (w/w). At different critical pH values, nisin/RL complexes and coacervates exhibited varied microstructural properties, with those formed at pH_opt (4.4-4.8) displaying the most intense microstructures. Electrostatic attractions were the primary driving force to give nisin/RL complex coacervation, with hydrophobic and hydrogen bond interactions playing fewer roles. Notably, complex coacervation, particularly at pH_opt, enhanced the thermal stability of nisin but reduced its crystallinity and secondary structure.

Therefore, our findings offer a theoretical basis for stabilizing the antibacterial agent nisin through complex coacervation. © 2025 Society of Chemical Industry.