Phase behavior and interaction mechanism of complex coacervation between nisin and carboxylic curdlan

Abstract

In this study, an anionic C6-carboxylic curdlan (C6-Cc) was selected to prepare complex coacervates with nisin and examined their phase behavior, microstructure, and interaction mechanisms. The results revealed that the characteristic pH values (pH_c, pH_φ1, pH_opt, pH_φ2) of the nisin/C6-Cc complexes were highly dependent on the mass ratio of C6-Cc to nisin within the phase diagram. As the mass ratio of C6-Cc to nisin decreased, the characteristic pH shifted toward higher values. The complex coacervates of nisin/C6-Cc at different phase states displayed significantly distinct microstructural properties, with the maximum complex coacervates formed at pH_opt showing large particle aggregates and compact microstructures. The primary driving force behind complex coacervation between nisin and C6-Cc was electrostatic attraction, with hydrophobic interactions and hydrogen bonding also contributing to the complexation process. Moreover, the complex coacervates formed at pH_φ1 exhibited notable viscoelastic behavior, dominated by elasticity due to strong electrostatic interactions.