## 3 Results and Discussion
### Rheological Behavior of Suero Costelo  
Figure 2 shows the flow curves for _suero costelo_ produced in the department of Cordoba, Colombia. Most rheograms (56%) show that the upward and downward curves coincide: there is no hysteresis phenomenon. Thus, this _suero costelo_ showed a time-independent behavior. On the other hand, some rheograms (44%) show no correlation between the upward and downward curves; that is, the phenomenon of hysteresis (dependence of behavior with time) is presented. For upward and downward curves, the comparison of independent means showed significant differences between treatments, which corroborates time dependence (thixotropy) in _suero costelo_ produced by some producers, mainly from the municipalities of Cienaga de Oro, Cerete, China, and Monteria, with a thixotropy comprising between 19.5 and 92.8% (Table 3). These high percentages of thixotropy may be due to the addition of some thickeners or stabilizers [46]. This behavior has been reported for dairy cream with some natural stabilizers [14; 47], ice cream [48], and yogurt [49]. Furthermore, for the _suero costelo_ that shows time dependence, the ascending curve is greater than the descending curve, so they show a positive thixotropy, where the viscosity decreases with time due to a change in the internal structure when a strain is applied. Experimental data were adjusted to the Ostwald-de Waele or power law model, which is the most used for dairy products and all adequately represented rheological data (R\({}^{2}\) between 88.4 and 97.9%). The flow behavior index of the rheograms shows values less than one (0.06 to 0.78) (see Table 3), which confirms the pseudoplasticity of _suero costelo_. This behavior is related to changes in the macromolecular organization and can be explained by the structural breakdown of the molecules due to the hydrodynamic forces generated and the increased alignment of the constituent molecules. As the shear rate increases, randomly positioned chains of polymer molecules align in the direction of flow, resulting in less interaction between adjacent polymer chains [50]. Similar results were found in creams with different fermentation levels [4], starch-milk dessert cream [47], low and high fat cream [14], recombined cream [21], sour creams supplemented with milk protein concentrate [6], and whipping cream [14; 51]. In general, dairy cream has shear-thinning behavior (pseudoplastic fluid) due to partially aggregated fat globules, which can be broken down at high shear rates [52]. Figure 2: Rheogram of artisanal _suero costelo_ produced in the department of Cordoba, Colombia. ANOVA shows that there are significant differences (\(p<0.05\)) between the rheological parameters of the power law (\(K\) and \(n\)) of the artisanal _suero costello_ produced by the different producers in the municipalities studied. This great variability is due to the raw materials used and the processing method. The flow behavior index (\(n\)) showed values between 0.17 and 0.78, except for some _suero costeno_ (C1, C2, and C3) produced in the municipality of Cerete (Cordoba, Colombia), which showed a flow behavior index of less than 0.10, so their rheological behavior is very pseudoplastic. The higher shear thinning behavior has the advantage of a decrease in the energy needed during the process conditions of the _suero costeno_ (pumping and mixing), and it is also related to a product with better sensory properties (texture).