## 3 Results and Discussion
### Rheological Properties  
Figures 2 and 3 illustrate the effects of the storage of yogurt dry ingredients on the rheological properties of the obtained yogurt. Small-amplitude oscillatory rheology with the measurement of storage modulus (G\({}^{\prime}\)), loss modulus (G\({}^{\prime\prime}\)) and loss tangent (LT) can be used to characterize the rheological properties of yogurts without damaging the gel matrix. The storage modulus and loss modulus show, accordingly, an elastic and viscous element in viscoelastic properties of yogurt. The loss tangent is a quotient loss modulus and storage modulus. Low values of loss tangent show that the material is much more elastic than viscous [38]. The rheological properties of the obtained yogurts were significantly affected by the storage of yogurt dry ingredients; the differences were statistically significant at the level of \(p<0.05\) (Table 4). As storage times and temperatures increased, the \(G^{\prime}\) of the yogurt samples decreased and the tan \(\delta\) increased. Yogurt samples were less elastic with a higher input of viscous properties [29]. As follows from Figures 2 and 3, to obtain yogurt with better rheological properties, yogurt ingredients must be stored at low temperatures. Higher temperature influenced the viability of starter cultures (Table 4), resulting in lower lactic acid production rates during the incubation of the recombined milk bases. Consequently, longer incubation times were required to acidify the medium up to pH 4.6. The integrity of casein micelles in milk is governed by a localized equilibrium between the hydrophobic interactions and the electrostatic repulsions. During fermentation, as the pH of milk decreases, the colloidal calcium phosphate (CCP) within the casein micelles is solubilized, particularly at pH levels below 6.0. This process is completed at approximately pH 5.0, causing partial rearrangement of the internal structure of the casein micelle. When CCP is dissolved within the casein particles, there is an increase in the electrostatic repulsion between the exposed phosphoserine residues. This weakens the casein-casein interactions and probably contributes to a slight decrease in the G\({}^{\prime}\) values. As the milk pH approaches its isoelectric point (i.e., pH \(<\) 5.0), the electrostatic repulsion decreases, which promotes the casein-casein attractions driven by the increased hydrophobic interactions. These factors promote bond formation/strength and thus increase gel stiffness, contributing to an increase in the G\({}^{\prime}\) values [29]. \begin{table}
\begin{tabular}{l c c c c c} \hline
**Storage temperature** & & 5 & & & 20 \\
**(\({}^{\circ}\)C)** & & & & & \\ \hline
**Storage time** & & & & & \\
**(weeks)** & 0 & 2 & 8 & 0 & 2 & 8 \\ \hline _Streptococcus thermophilus_ & 8.2\({}^{\text{ a}}\) & 8.19 \({}^{\text{ a}}\) & 8.16 \({}^{\text{ a}}\) & 8.2\({}^{\text{ a}}\) & 7.98 \({}^{\text{ a}}\) & 7.56 \({}^{\text{ b}}\) \\ (logCFU/g) & (0.06) & (0.05) & (0.02) & (0.06) & (0.03) & (0.08) \\ \hline _Lactobacillus delbrueckii_ & & & & & \\
**subsp. lactis** & 8.54 \({}^{\text{ a}}\) & 8.49 \({}^{\text{ a}}\) & 8.47 \({}^{\text{ a}}\) & 8.54 \({}^{\text{ a}}\) & 8.07 \({}^{\text{ b}}\) & 7.85 \({}^{\text{ c}}\) \\ _Lactobacillus acidophilus_ & (0.05) & (0.04) & (0.03) & (0.05) & (0.02) & (0.03) \\ \hline _Bifdobacterium lactis_ & 8.11\({}^{\text{ a}}\) & 8.09 \({}^{\text{ a}}\) & 8.05 \({}^{\text{ a}}\) & 8.11 \({}^{\text{ a}}\) & 7.85 \({}^{\text{ b}}\) & 7.26 \({}^{\text{ c}}\) \\ (logCFU/g) & (0.05) & (0.04) & (0.03) & (0.05) & (0.03) & (0.07) \\ \hline \end{tabular} Standard deviation is shown in brackets; means within a row followed by various letters (a–c) are significantly different (\(p<0.05\)).  
\end{table} 
Table 4: Bacteria counts (log CFU/g) in yogurt dry ingredient mixture after storage at 5 \({}^{\text{ o}}\)C and 20 \({}^{\text{ o}}\)C for different periods of time.