## 3 Results and Discussion
### Evaluation of Viscosity of Smoothie Samples  
The rheograms and viscosity curves of the control and treated smoothie samples on days 0 and 14 are shown in Figure 2, while Table 5 demonstrates the parameters, the goodness of fitting of the Herschel-Bulkley model, and a comparison of selected apparent viscosity values. It can be observed that there is a non-linear relation between shear rate and shear stress, and shear rate and apparent viscosity in the range of 10 and 1000 s\({}^{-1}\), which proves the non-Newtonian rheological behaviour of the samples. The convex profile of the flow curves and the flow behaviour index values (0 \(<\) _n \(<\)_1) indicate that the smoothie samples exhibited shear-thinning (pseudoplastic) flow behaviour. With increasing shear rate, pseudoplastic behaviour shows increasing shear stress values and decreasing apparent viscosity values as the molecular interactions are weakened ([PERSON], 2017). The pseudoplastic flow behaviour of fruit smoothie samples has been observed by numerous researchers ([PERSON], 2017; [PERSON], 2017; [PERSON], 2017).  
It is also important to note that all the tested samples had a yield stress, indicating that a minimum shear stress is necessary to enable the samples to flow [58]. Moreover, the observed fluctuation in the apparent viscosity within the small shear rate range (10-73.6 s\({}^{-1}\)) in the case of all stored samples suggests inhomogeneity in the texture.  
The yield stress value was the sole parameter of the Herschel-Bulkley model that was able to differentiate the samples in our study to a statistically significant extent. Significant differences were observed in this parameter between the fresh and stored samples in all cases. After storage, a smaller shear stress is required to induce flow. Considering the fresh samples, it can be concluded that the effect of the applied gentle preservation procedures is not significant on the yield stress of the prepared smoothie sample. However, a significant difference can be seen between the control sample and the first heat-treated and then pressure-treated sample after storage.  
A similar trend can be seen in the apparent viscosity values at lower (100 s\({}^{-1}\)) and higher (1000 s\({}^{-1}\)) shear stress. The only difference is that after storage, both treated samples were significantly different from the control sample. It can be concluded that for fresh samples, the impact of treatment on apparent viscosity is undetectable at the shear rates examined, but storage clearly reduced the viscosity of all samples. After storage, the 60 \({}^{\circ}\)C-250 MPa sample was most similar to the fresh samples, and the control sample showed the greatest reduction in viscosity. This finding contrasts with the results of the sensory evaluation, wherein the judges perceived the control sample to be the densest. It is likely that the inhomogeneous particles in the sample led to this perception of density.  
The direction of changes in the consistency coefficient followed the trends observed for viscosity, but the differences were not significant in either case. It was also reported by [43] that the consistency coefficient does not reflect the variation in the apparent viscosity.