Tunable Yield Stress of Aqueous Dispersions of Hydrophobically-Modified Phytoglycogen Nanoparticles

Phytoglycogen is a natural polysaccharide produced in the form of compact, 44 nm diameter nanoparticles in the kernels of sweet corn. Its highly branched, dendrimeric structure leads to interesting and useful properties that make the particles ideal as unique additives in personal care, nutrition and biomedical formulations. The properties of phytoglycogen can be readily altered through chemical modification. We consider a hydrophobic modification of phytoglycogen by covalently attaching charged, hydrophobic octenyl succinic anhydride (OSA) chains to the weakly charged, hydrophilic surface of phytoglycogen. When dispersed in water at moderate concentrations (C ~ 20% w/w), the OSA-modified particles form a shear-sensitive gel with a low shear viscosity that exceeds by a factor of ~10⁶ that of native phytoglycogen dispersions of the same concentration. Furthermore, the dispersions exhibit a well-defined yield stress, as measured using different rheology techniques. The yield stress vanishes as the pH of the dispersions is reduced below the pKa of the acidic group of OSA, with the material transitioning from a shear-sensitive gel to a flowing liquid. This pH-sensitivity suggests new applications for OSA-modified phytoglycogen.