Complexation of sodium caseinate with gum tragacanth: Effect of various species and rheology of coacervates

We investigated complex coacervation of sodium caseinate/Astraga/us rahensis (A.r) as a function of pH with light scattering, spectrophotometry, and viscosity measurements. Interestingly, sodium caseinate/As displayed five structural transitions; pH similar to 7.00 to pH similar to 5.40: no interaction occurred, pH similar to 5.40 to pH similar to 4.80: initiation of the formation of primary soluble complexes, pH similar to 4.80 to similar to 4.30: formation of interpolymer complexes, pH similar to 4.30 to similar to 4.02: optimum coacervation and pH similar to 4.02 to similar to 2.50: suppression of coacervation. In addition, rheological properties of sodium caseinate/A.r coacervates were studied at various pH values. A much higher storage modulus (G') than loss modulus (G '') for all sodium caseinate/A.r coacervates suggests the formation of highly interconnected gel-like network structures with mainly elastic behaviour. Moreover, sodium caseinate/A.r coacervates at all pH values exhibited a shear thinning behaviour across the entire shear rate range investigated. Effects of different species of gum tragacanth on the interactions with sodium caseinate have been scarcely studied. Our study showed that systems containing various species (A.r, soluble fraction of A.r and Astragalus gossypinus (A.g)) had different critical pH values and particle sizes during complex coacervation, which could be due to different ratio of soluble to insoluble fractions and uronic acid content of various species. (C) 2014 Elsevier B.V. All rights reserved.