Soy protein-polysaccharide complex coacervate under physical treatment: effects of pH, ionic strength and polysaccharide type

The objective of this paper is to explore the effects of pH, ionic strength and polysaccharide type on the aqueous phase behaviors and rheological properties of soy protein isolate-chitosan (SPI-CS) and soy protein isolate-carboxymethyl cellulose (SPI-CMC) coacervates treated by vortex fluidic device (VFD) and shear homogenization. Characterization in terms of phase behavior and microstructures depicted that the VFD and shear homogenization treatments affected only the SPI-CS complex. According to the ζ-potential values at tested pHs (3.0–8.0), both physical processing had insignificant effect on charge stabilization of protein-polysaccharide complex. Both the SPI-CS coacervates (at pH 7.0) and SPI-CMC coacervates (at pH 3.0) showed gel-type rheological behaviors (G′ > 1000 Pa), suggesting that the SPI and polysaccharides did not form complex coacervate (liquid in nature) but interpolymeric complex (solid in nature). In the absence of salt ions, independent on the type of coacervate, VFD slightly decreased the modulus (G′ < 1000 Pa) while homogenization significantly decreased the modulus (G′ < 20 Pa). Alternatively, the addition of salt ions produced an electrostatic shielding and weakened the protein-polysaccharide electrostatic interaction, resulting in a decrease of coacervate modulus. Interestingly, under certain condition, VFD treatment probably promoted the interaction between protein molecules in protein-polysaccharide coacervate, resulting in another increase in the elastic modulus of the complex coacervate.