Complex coacervation in pea protein isolate–chitosan mixtures

Protein–polysaccharide interactions play an essential structure-controlling role in foods and biomaterials. Turbidity and electrophoretic mobility measurements were used to investigate the formation of soluble and insoluble complexes between pea protein isolate (PPI) and the cationic polysaccharide, chitosan (Ch) as a function of pH and biopolymer mixing ratio (1:1–20:1 PPI–Ch). In addition, pH-induced conformational changes of PPI upon complexation with Ch were studied by fluorometry. As the PPI–Ch mixing ratio increased from 1:1 to 12.5:1, critical structure forming events (i.e., those associated with the formation of soluble and insoluble complexes) shifted to higher pHs, and progressively behaved similar to those for PPI alone. At biopolymer ratios > 15:1, mixed systems resembled that of PPI alone. Changes to the tertiary conformation of PPI upon complexation with Ch at a 7.5:1 biopolymer ratio were found to occur at pH 6.2, corresponding to the presence of insoluble complexes.