Influence of pH and temperature on the rheological properties of aqueous dispersions of starch–sodium palmitate complexes

Aqueous dispersions of high-amylose corn starch were steam jet cooked and blended with aqueous solutions of sodium palmitate to form amylose inclusion complexes. The rheology of dispersions of these complexes was examined. Acetic acid was added to reduce the pH, converting complexed sodium palmitate to palmitic acid. Associations of the complexed palmitic acid and reduced electrostatic repulsion resulted in a sharp increase in the linear viscoelastic properties of the materials. Further reduction of the pH led to precipitation of palmitic acid complexes and a decrease in the gel strength. Temperature ramps showed a sharp, reversible decrease in the elastic modulus. The temperature at which this decrease occurred depended on both the concentration and pH.