Zein Protein Nanoparticles: Fabrication and Rheology of Their Dispersions in Polysaccharides

Zein protein nanoparticles are fabricated in two anionic polysaccharides, sodium carboxymethyl cellulose (CMC) and xanthan gum (XG), using the anti-solvent method. The rheological behavior and surface-active properties of dispersions of zein nanoparticles in polysaccharides are investigated. Two sets of experiments are carried out. In one set, the zein concentration is fixed at 1 wt% and the concentrations of the polysaccharides varied from 0 to 1 wt% in increments of 0.2 wt%. In the second set of experiments, the zein concentration varies from 1 to 5 wt% at a fixed polysaccharide concentration of 0.5 wt%. The SEM images clearly show the formation of zein nanoparticles in polysaccharides. Polysaccharide solutions and zein nanoparticle-polysaccharide dispersions exhibit shear-thinning rheological behavior and follow the power-law model adequately. With the addition of zein, the consistency of zein nanoparticle-CMC dispersions increases, and they become more shear-thinning in comparison to pure CMC solutions. With the increase in zein concentration at a fixed CMC concentration, the consistency rises sharply up to 4 wt% zein concentration and then drops substantially, with a further increase in zein concentration. The addition of zein to XG solutions exhibits a more complex rheological behavior. The consistency index decreases with the addition of zein to XG solutions when XG concentration is less than 0.7 wt%. At higher XG concentrations, the consistency index increases with the addition of zein to XG solutions. With the increase in zein concentration at a fixed XG concentration, the consistency decreases substantially over the full range of zein concentration investigated. The surface tension of CMC solutions is strongly affected by the addition of zein nanoparticles. It decreases substantially with the addition of zein to CMC solutions. The surface tension behavior of zein nanoparticle-XG dispersions is like that of zein nanoparticle-CMC dispersions. The transitions in rheological and surface-active properties of zein nanoparticle-polysaccharide dispersions are explained in terms of microstructure of the dispersions.