Complex coacervation between β-lactoglobulin and acacia gum in aqueous medium

The compatibility of beta-lactoglobulin (beta-lg) and acacia gum in aqueous medium was investigated as a function of the pH (3.6-5.0), the protein to polysaccharide weight ratio (50:1-1:20) and the total biopolymer concentration (0.1-5 wt%). The ternary phase diagrams obtained at low ionic strengths (0.005-10.7 mM) typically accounted for phase separation through complex coacervation. Thus a drop-shaped two-phase region was anchored in the water-rich corner. The electrostatic nature of the interactions between the two biopolymers was pointed out according to the pH dependence of the two-phase region's breadth. Following the absorbance of the mixtures at 650 nm, the influence of the protein to polysaccharide ratio was also demonstrated. Electrophoretic mobility (mu(E)) measurements and chemical analyses of separated phases revealed the formation of soluble and insoluble coacervates and complexes. A remarkable value of the protein to polysaccharide weight ratio (2:1) at pH 4.2 gave the same protein to polysaccharide (Pr:Ps) ratio in the two phases after 2 days, implying that electrostatic interactions are maximum between beta-lg and acacia gum. The increase of the total biopolymer concentration reduced the influence of pH and protein to polysaccharide ratio. Also, the increase of the pH close to the beta-lg IEP reduced the influence of the total biopolymer concentration and Pr:Ps ratio. As the biopolymer content was increased at pH 3.6 and 4.2, the relative beta-lg solubility increased probably because of the self-suppression of complex coacervation. (C) 1999 Elsevier Science Ltd. All rights reserved.