Complex coacervation of pea protein isolate and alginate polysaccharides

Complex coacervation between pea protein isolate (PPI) and alginate (AL) was investigated as a function of pH (1.50-7.00) and mixing ratio (1:1-20:1 PPI:AL) by turbidimetric analysis and electrophoretic mobility during an acid titration. Conformational changes to the secondary structures during coacervation were also studied by Raman spectroscopy. Critical structure-forming events associated with the formation of soluble (pH 5.00) and insoluble (pH 2.98) complexes were found for a 1:1 PPI-AL mixture, with optimal biopolymer interactions occurring at pH 2.10 (pH(opt)). As mixing ratios increased between 4:1 and 8:1, critical pHs shifted towards higher pH. Maximum coacervate formation at pH(opt) occurred at a mixing ratio of 4:1. Electrophoretic mobility measurements showed a shift in net neutrality from pH 4.00 in homogenous PPI solutions, to pH 1.55 for the 1:1 mixture. As biopolymer ratios increased towards 8:1 PPI:AL, net neutrality shifted to higher pHs (similar to 3.80). Raman spectroscopy revealed minimal complexation-induced conformational changes. Findings could aid in the design of pH-sensitive biopolymer carriers for use in functional food and bio-material applications. (C) 2011 Elsevier Ltd. All rights reserved.