## 3 Results and Discussion
### Rheological and Textural Characteristics  
The rheological parameters of the product are closely related to the shaping of its macroscopic features, e.g., consistency or physical stability, which depend on the mechanical properties and structure at the microscopic level. Therefore, their determination is necessary for creating the qualitative characteristics of the food product. The technique of dynamic light scattering enables non-contact and non-destructive analysis as a function of time, based on the movement and interactions between system molecules [17; 18]. Passive methods of microrheology analysis that allow non-invasive tracking of diffusive motion of molecules are particularly useful in studies of heterogeneity of food systems. In combination with other techniques, they can provide detailed characteristics of food products, both at the stage of their production and distribution or use [24]. Microrheological properties of samples were analyzed during 24 h stabilization at 20 \(\pm\) 1 \({}^{\circ}\)C. The MSD (mean square displacement) curves as a function of decorrelation time were obtained. Based on the position of the first curve and the last curve, a decrease in MSD level over time was noted, which indicated a reduction in mobility of molecules in the systems. The shape of the MSD curve evolved with the passage of time, and it was characterized by an increasingly visible non-linear course and a shift in the longer time of decorrelation (Figure 2). Moreover, a clear accretion in the EI value was observed up to approx. four hours of measurement, especially for samples with 6%, 9%, 12% or 15% prebiotic content. Subsequently, these changes progressed slightly and it can be assumed that after 12 h the EI values for all samples were at a relatively constant level (Figure 3). Both MSD curves and EI curves show that the thickening (3%) and/or gelling (6%, 9%, 12%, 15%) process of stirred yogurts was initiated by inulin addition. Therefore, a significant relationship between inulin concentration and viscoelastic properties of yogurts was demonstrated. As the amount of inulin addition increased, their elasticity and viscosity were enhanced. This effect was most noticeable in the case of the sample with the highest inulin content, i.e., at the level of 15% _w/w_. Other research also presents that the formation of the gel and its rheological properties depend on the inulin concentration, temperature and mixing intensity during preparation. Increasing inulin concentration, heating to approx. 70-80 \({}^{\circ}\)C and/or mixing of the system promote the gelling properties of inulin. However, it is possible to obtain the gels at lower temperatures. Such a process is slightly more intense with a higher inulin content [25; 26]. Figure 1: Total acidity (\({}^{\circ}\)SH) 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, \(p<0.05\)). [PERSON] et al. [27] used the MS-DWS method to evaluate the acid-induced gelation of skimmed milk. At neutral pH conditions, a uniform linear increase in MSD was observed during decorrelation, which could be attributed to liquid-like behavior. With the acidification of the milk, the MSD level decreased and the profile formed into a characteristic \"plateau\" in a longer period of decorrelation. Thus, the progressing gelation process was demonstrated. Similar results were obtained by [PERSON] et al. [28], who observed that the gel properties of milk depend on the exopolysaccharideader used, based on EI curves as a function of time. The microrheological attributes of yogurts stored for 24 h at 6 \({}^{\circ}\)C were determined, using the MS-DWS method. Figures 4 and 5 show the correlation of EI, MVI and SLB parameters to the inulin content. An exponential increase in the value of EI or MVI as a function of the increase in the concentration of this prebiotic was noted (R\({}^{2}>\) 0.90). Yogurts with 12% and 15% inulin content demonstrated approx.