Characterisation of gum tragacanth (Astragalus gossypinus)/sodium caseinate complex coacervation as a function of pH in an aqueous medium

The formation of electrostatic complexes between sodium caseinate and gum tragacanth (Astragalus gossypinus, A.g) as a function of pH (7.00-2.50), the biopolymer mixing ratio and the total biopolymer concentration was studied by spectrophotometric and light scattering measurements.This multi-methodological approach allowed us to demonstrate the critical structure-forming pHs associated with the formation of soluble and insoluble complexes for the sodium caseinate/A.g mixture. The phase transition of sodium caseinate/A.g complexed/coacervated system was explained by monitoring the absorbance profiles as a function of time.Particle size measurements revealed a progressive decrease in the complex/aggregate size while lowering the pH until reaching a minimum (pH 4) at which nanoparticles (70 nm) formed.As the mixing ratio of protein to polysaccharide increased from 1:1 to 3:1, the critical pHs shifted towards higher pH values. Conversely, for a constant mixing ratio, higher levels of total concentration resulted in an increase in the maximum turbidity but had no meaningful effect on pHC (similar to 5.89) and pH(Phi 1) (similar to 4.00). (C) 2012 Elsevier Ltd. All rights reserved.