Hardening and Softening Properties of Soybean Protein-water Suspending Systems

Abstract

The apparent viscosities of glycinin (11S), β-conglycinin (7S) and acid-precipitated protein (APP) of soybean suspending systems and their heated gels were investigated using a modified coaxial cylinder viscometer. A hybrid program was established: (i) cyclic temperature test (20→90→20°C) under constant shear rate and (ii) cyclic shearing test (48.7→243.7→ 48.7 sec−1) under isothermal conditions. The viscosities of the soy protein suspending system (12 %, w/v) gradually decreased with increasing temperature to about 70°C. Thereafter, characteristic behavior depended upon the sort of soy protein. The apparent viscosity of 7S globulin increased considerably, especially at lower ionic strength (μ =0.01). However, the viscosity of 11S globulin remained almost unchanged under the different temperatures and ionic conditions used. A considerable increase in viscosity was found in the cooling process rather than in the heating process with 7S globulin and APP. A noticeable thioxotropic characteristic was found in...