In this study, the complex coacervation of whey protein isolate (WPI) and quince seed mucilage (QSM) was studied as a function of pH (7.0–2.0), biopolymers concentration (0.05, 0.1 and 0.5%) and WPI:QSM ratio (10:90 to 90:10), according to protolytic titration, electrical conductivity (EC) and turbidity analyses. The solution containing 0.5% biopolymers with WPI:QSM ratio of 70:30 resulted in maximum complex coacervation at the pHopt 4.0. With increasing WPI:QSM ratio, the peaks of pH-turbidity curves shifted to higher pH values, and with increasing biopolymers concentration, the optimum WPI:QSM ratio and pH shifted to higher values. The EC of biopolymers solutions (concentration 0.5%) increased by decreasing pH and WPI:QSM ratio. The aforementioned optimum condition resulted coacervates with maximum particles size (16.22 μm) and minimum ζ-potential (−5.1 mV), which were observed as densely agglomerated macro-complexes with highest coacervation yield (80.67%). The X-ray analysis showed that coacervates retain the amorphous structure of individual biopolymers. These coacervates may be useful for encapsulation and delivery of (bio-) active compounds.
