Ultrasonic-induced Modification of Flow Properties of Soy Protein Dispersion

Abstract

The heat-treated acid precipitated proteins (H-APP), as intermediates in the commercial, production of isolated proteins from defatted soybeans, were dispersed under an ultrasonic power field over a protein concentration range from 5.4 to 12.6%.
The ultrasonically untreated H-APP dispersions showed a pseudoplastic flow behavior, which was characterized by shear rate thinning, giving a yield value above 9.0%. With prolongation of the ultrasonic exposure duration, a rapid decrease in the apparent viscosity of resultant dispersions was observed under the condition of 200W/100g, with a rapid increase in flow behavior index according to the power law. In addition, ultrasonication induced the rise in critical concentration for the yield value up to 12.6%. As a result, the flow of 120 sec-irradiated dispersions became almost Newtonian at a concentration of 5.4-9.0%, but remained pseudoplastic above this range.
The result obtained from gel filtration revealed that these changes in flow properties are derived from a dissociation of the protein aggregates which have formed through heat treatment of the APP prior to ultrasonication. Furthermore, the ultrasonic-induced structural alteration was considered to be associated with a partial cleavage of intermolecular hydrophobic interactions rather than with peptide-, or disulfide-bonds.
Mechanical treatment such as ultrasonication is considered to be practically applicable in the production of soy protein foods, providing a significant improvement in the efficiency of unit processes such as pumping, piping, and spray drying, due to its ability to modify the flow properties of protein dispersions.