Effect of Pectin Type on Association and pH Stability of Whey Protein-Pectin Complexes

The purpose of this study was to investigate the influence of pectin type on complex formation between whey protein isolate (WPI) and high methoxy pectins with varying degrees of esterification (DE), and their pH stability. The biopolymer particles with protein-to-polysaccharide mass ratio set to 2:1 were formed at pH 3-7 by heating at 85 A degrees C for 20 min. The particle size, electrical charge, turbidity and microstructure of the biopolymer complexes were evaluated. The optimal conditions for forming WPI-pectin complexes were at the initial pH of 4.5-4.75, just below the isoelectric point of the WPI, where complex formation occurs. At this pH range, the smallest biopolymer complexes (d = 225-300 nm) could be created. Pectins with 50, 55, 62 and 70 % DE formed relatively small and monomodal complexes with WPI, except for pectin with 71 % DE, which showed major aggregation. The pH stability against aggregation was best with the biopolymer complexes assembled from pectins with 50 % DE (stable at pH 3.5-6.0) and with 62 % DE (stable at pH 3.0-6.0). The results suggest that pectins with varying DE can be used to form small particles and therefore can offer new possibilities in designing novel hierarchical structures and delivery systems.