## 3 Results and Discussion
### Rheological Properties
The CCP solubilization in milk during acidification is a slow process and may require a slightly lower pH for complete dissolution of CCP under fast acidification conditions (i.e., high inoculation rates can be less efficient in solubilizing CCP, as there would be less  
Figure 3: Effects of storage temperature and time (in weeks), applied to yogurt dry ingredients, on the loss modulus (G\({}^{\prime\prime}\)) of yogurt made from stored powders. Results show storage modulus at three selected points of the applied stress amplitude range (**A–C**). Figure 2: Effects of storage temperature and time (in weeks), applied to yogurt dry ingredients, on the storage modulus (G\({}^{\prime}\)) of yogurt made from stored powders. Results show storage modulus at three selected points of the applied stress amplitude range (**A–C**). time at any particular pH value during milk acidification). When CCP dissolves at a lower pH, caseins can be less susceptible to excessive rearrangements. This is due to the fact that at lower pH values, there will be lower electrostatic repulsion and higher hydrophobic interactions between casein particles, which promotes stiffer gel networks with higher G\({}^{\prime}\) values [29]. For this reason, higher levels of viability of the starter culture resulted in acid milk gels with higher G\({}^{\prime}\) and lower tan \(\delta\) values. Table 5 shows all collected data of the physical properties of yogurt obtained from dry ingredients stored at different conditions. Based on the results presented in Table 5, multivariate Pearson correlation was made. The coefficients of correlation are shown in Table 6.  
The dynamic rheological properties, ultrasound viscosity as well as yogurt firmness increased for the yogurt dry ingredients stored at a lower temperature for a shorter period of time (Table 5). The highest values of yogurt firmness (0.209 N), ultrasound viscosity (369 mPas-gcm\({}^{-3}\)), and storage modulus (22.8 Pa), and the lowest value of tan delta (0.261) were observed in yogurt obtained from dry ingredients stored for 2 weeks at 5 \({}^{\circ}\)C. Interestingly, similar yogurt firmness values were observed by [PERSON] et al. [39], applying the penetration test method. There was a strong correlation between the firmness of yogurt and ultrasonic viscosity (R\({}^{2}\) = 0.98) (Table 6). Both methods involve puncture of the sample. A lower correlation coefficient value was noted for correlation between firmness and storage modulus (R\({}^{2}\) = 0.73), which is measured at low strain, without fracture of the sample. A strong negative correlation was found between the dry yogurt topography and wet yogurt ultrasound viscosity and storage modulus (R\({}^{2}\) = 0.98 and 0.84, accordingly) (Table 6). Time and temperature storage of yogurt dry ingredients influenced the microstructure of the final product and its viscosity. The formulation stored at a lower temperature and for a shorter time resulted in a more viscous and more elastic product with smaller surface roughness. More rapid drops in pH can lock the protein into a more dispersed structure with a smoother surface and greater density of possibly stronger strands [40]. The smoothest surface of dry yogurt (412 nm) was observed in yogurts derived from dry ingredients stored for 2 weeks at 5 \({}^{\circ}\)C. Furthermore, this yogurt also had the best rheological properties (Table 5). A linear correlation was also found between all measured rheological properties and water activity of yogurts (R\({}^{2}\) = 0.86) (Table 6). Yogurts with a stronger and more elastic texture were characterized by smaller water activity. [PERSON] et al. [41] investigated changes in the physicochemical properties of yogurt with the added whey protein concentrate (WPC). In most investigated cases, water activity decreased as the WPC content and yogurt firmness increased, regardless of the strain type. [PERSON] et al. [42] made water activity measurements as a tool for predicting structural and mechanical properties during dewatering and ageing of sludge. Strengthening the