## 3 Results and Discussion
### Rheological and Textural Characteristics
2- and 3-fold higher EI and MVI values, respectively, than natural yogurt  
Figure 3: Elasticity indexes (EI) of yogurts with 0%, 3%, 6%, 9%, 12% or 15% _w_/_w_ inulin addition during 24 h stabilization at 20 \({}^{\circ}\)C.  
Figure 2: Mean square displacement (MSD) curves of yogurts with 0%, 3%, 6%, 9%, 12% or 15% _w_/_w_ inulin addition during 24 h stabilization at 20 \({}^{\circ}\)C (first curve—at the top of profile, last curve—at the bottom of profile). (\(p<0.05\)). The SLB value was not changed appreciably by the amount of inulin added--for the control sample it was approx. 0.524 nm\({}^{2}\), and for yogurt with 15% inulin content approx. 0.502 nm\({}^{2}\) (Figure 5). All stirred yogurts were characterized by SLB values higher than 0.5 and lower than 1.0, which means that the liquid phase dominates in these systems. Similar relationships were obtained by [PERSON] et al. [25], who used inulin (0%, 3% or 6% _w/w_) as a fat replacement in a blend of reconstituted milk, which was subjected to rennet coagulation (at 32 \({}^{\circ}\)C). Samples with inulin had a higher elasticity modulus than the sample without inulin. However, the insertion of inulin into the mixture in an amount of 3% or 6% did not have a significant impact on the value of tangent \(\delta\) (G'/G\"). In turn, [PERSON] et al. [29] assessed the effect of enriching yogurt in various fiber preparations (from peas, oats, wheat or inulin) at 1%, 1.5%, 2.0% or 2.5% _w/w_. Increasing the inulin concentration from 1% to 2.5% resulted in a 2-fold higher elasticity modulus, while tan \(\delta\) did not change significantly. It has been demonstrated that as the shear rate increases, the dynamic viscosity of yogurt decreases, as shown at a double logarithmic scale. All samples tested, regardless of the amount of additives prebiotic addition, were non-Newtonian (shear thinning) fluids. In general, the viscosity of yogurt increased with the higher inulin content, which was particularly evident at lower shear rates (Figure 6). Another slight relationship was proved by [PERSON] et al. [30], who added quinoa flour to the recipe of yogurt (0.2%, 0.6%, 1.0%, 1.4% or 2.0% wt/vt). It has been shown that a quantity of additive exceeding 1.0% caused a deterioration of yogurt quality. The sample containing 0.6% quinoa flour was considered the best. It was characterized by the highest viscosity, the lowest degree of syneresis and good porosity of the protein network. Figure 4: Elasticity indexes (EIs) and macroscopic viscosity indexes (MVIs) of yogurts with 0%, 3%, 6%, 9%, 12% or 15% _w/w_ inulin addition (a, b, c... --various letters for average values mean statistically significant differences, \(p<0.05\)). Figure 5: Solid-liquid balance (SLB) of yogurts with 0%, 3%, 6%, 9%, 12% or 15% _w/w_ inulin addition (a, b, c... --various letters for average values mean statistically significant differences, \(p<0.05\)). Other studies have also investigated that the type and concentration of the substance, enriching the composition of the product, have an influence on its integrity and durability. Dietary fiber preparations are effective structure-forming additives in dairy products [21; 31; 32]. Texture analysis indicated that the inclusion of inulin into natural yogurt caused an increase of its firmness and stickiness. Stirred yogurt with a 3% inulin concentration did not have differing textural parameters from the control sample (\(p>0.05\)). A further increase in fiber concentration in the system caused a significant increase in the cohesion of the yogurt structure. These results also confirm the emulsion stabilizing effect of inulin. Samples with 12% and 15% inulin content were characterized by 3- and 5-fold higher values of firmness and stickiness, respectively, compared to yogurt without addition (Figure 7). Therefore, the use of inulin as a functional additive to natural yogurts can not only improve their nutritional value, but also their physical stability.