Non-linear Rheological Properties of Soy Protein Isolate Dispersions and Acid-Induced Gels

This study presents the non-linear viscoelastic properties of soy protein isolate (SPI) dispersions and acid-induced gels to considerable detail. The storage (G′) and loss (G′′) moduli of SPI dispersions showed Type III (week strain overshoot) and Type IV (strong strain overshoot) networks when the strain amplitudes varied between 0.01 and 1.00 and 1.00 to 100.00, respectively. In the case of acid-induced SPI gels the rheological parameters showed the characteristics of Type I (strain thinning) network. Fourier transform rheological experiments showed that the higher harmonic curves obtained u strain sweep test showed quite different shapes for SPI dispersions and gels. In the case of dispersions, the highest I 3/1 (0.101) occurred at the strain amplitude of 0.40 and then decreased to below 0.02. In the case of acid-induced SPI gels, the I 3/1 value began to be appreciable at the strain amplitude of 0.1 increased rapidly to its highest value (I 3/1 =0.05).