Phase behavior, thermodynamic and microstructure of concentrated pea protein isolate-pectin mixture: Effect of pH, biopolymer ratio and pectin charge density

The impact of pH, pea protein isolate (PPI)–pectin mixing ratio and pectin charge density on phase behavior (co-solubility, soluble complex and complex coacervates) of concentrated biopolymer mixture was investigated using state diagram and ζ–potential measurement. The microstructure, thermodynamic behavior, and non-covalent bonding of PPI to pectin were further explored by confocal laser scanning microscopy (CLSM), isothermal titration calorimetry (ITC), and Fourier transform infrared spectroscopy (FTIR). In general, the pH of soluble complex, complex coacervate formation shifted towards higher pH as PPI–pectin mixing ratio increased. Low methoxyl pectin (LMP) is favorable for complex coacervate over a wider pH range compared with high methoxyl pectin (HMP) due to its higher overall charge density. The CLSM images revealed that larger aggregates were formed in PPI-LMP coacervates. Both ITC and FTIR analyses indicated that soluble complex and complex coacervates were formed through the electrostatic interaction and hydrogen bonding between PPI and pectin.