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

Abstract

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 (∼5.89) and pHΦ1 (∼4.00).