In this study, the electrostatic interactions between quince seed mucilage (QSM) and whey protein isolate (WPI) were investigated by analysis of ζ-potential, turbidity, coacervation yield, and phase diagram. The maximum values of turbidity (2200 NTU) and coacervation yield (80.7%) were observed at the optimum values of WPI to QSM ratio (70:30) and pH (4). The soluble and insoluble complexes formed at the critical pH values of 5.5 and 5, respectively, while the biopolymers complexes decomposed at pH 2.5. SEM analysis revealed the coacervates as semi-spherical particles smaller than 200 nm, which aggregated without detectable porosity. The FTIR spectra showed that both electrostatic interactions and hydrogen bonds are important in the formation of WPI–QSM coacervates. The peaks in the DSC thermogram of coacervates were similar to those in WPI's but shifted and became smaller. These coacervates may be useful for the encapsulation of active substances.
