The favoring of a pseudoplastic behavior probably occurred due to higher-molecular-weight polymers formed during the cross-linking reaction promoted by the TG. Innocente, Comparin, and Corradini (2002) affirmed that with an increase in the shear rate, large polymer molecules tend to disentangle and possibly align in the flow field, offering less resistance to flow. The rheological behavior of the samples after the reduction of shear rate (downward curves) can
be seen in Table 3. Using the Power Law model it was observed that K varied from 0.08 to 0.15 Pa s−1, values Crizotinib clinical trial which are lower than those obtained for the upward curve. All samples containing TG had higher K values than the respective samples without TG, demonstrating that the addition of TG gives the ice cream a greater resistance to structural rupture. Moreover, the values of the flow behavior index (n) were greater than those of the upward curve, showing that there was a decrease in the pseudoplastic properties when the shear rate decreased.
The decrease in K and increase in n can be attributed to the structural breakdown ABT888 of the protein network of the ice cream due to shearing, which favors this behavior. An important feature of the shear stress versus shear rate results, obtained by increasing and then decreasing the shear rate, is the formation of Atorvastatin hysteresis. The area formed between the curves indicates that the fluid viscosity is time dependent (Tárrega, Durán, & Costell, 2004). Table 4 shows the hysteresis values for the ice cream samples. It can be observed that the TG addition caused an increase in the degree of hysteresis when compared with the controls
(without TG). Samples IC4-TG and IC6-TG (Table 4) showed the greatest degree of hysteresis with no significant differences (P < 0.05) between them. This demonstrates that these two samples needed more energy to break the ice cream structure formed from the protein polymerization, providing a firmer product. IC4-TG and IC6-TG were also the samples that showed the highest apparent viscosity and consistency index. According to Tárrega et al. (2004), a high-viscosity thixotropic fluid may show a larger hysteresis area than a lower viscosity one, even if the latter undergoes a more accentuated destruction of the structure. The presence of hysteresis was also observed by González-Thomás et al., (2008) and Karaca et al. (2009) in studies on ice cream. The time-dependent rheological data were fitted using the Weltman model in order to characterize the thixotropic behavior of the ice cream samples. It was observed that the TG addition resulted in a significant increase in the initial tension required (A) to initiate the breaking of the ice cream structure ( Table 5) due to the formation of a more stable network.