## 3 Results and Discussion
### Microstructure and Microrheology of Symbiotic Yogurt  
The microstructure of the desirable symbiotic yogurt (S3) was further studied in comparison with the control plain yogurt (S1) by scanning electron microscope. As shown in Figure 4B,D, the symbiotic yogurt exhibited a more dense, compressed, and homogeneous microstructure with no or negligible spaces, and the whey was firmly restrained in the gel matrix. The _S. boulardii_ cells were also visible with buds, confirming their viable and multipliable state at the end of storage (Figure 4E). In contrast, the plain yogurt showed an irregular branched network with wide spaces (Figure 4A,C). Previously, incorporation with gelatin in camel milk yogurt also resulted in a more compact and homogeneous protein network structure with reduced syneresis, mainly due to inter- and intra-molecular polymeric interactions in the yogurt [35; 39]. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{4}{c}{**Color and Appearance**} & \multicolumn{4}{c}{**Taste and Odor**} & \multicolumn{4}{c}{**Texture**} & \multicolumn{4}{c}{**Overall Acceptability**} \\ \cline{2-13}  & \multicolumn{4}{c}{**Storage/Day**} & \multicolumn{4}{c}{**Storage/Day**} & \multicolumn{4}{c}{**Storage/Day**} & \multicolumn{4}{c}{**Storage/Day**} & \multicolumn{4}{c}{**Storage/Day**} \\ \cline{2-13}  & **0** & **7** & **14** & **21** & **28**  
Microrheology measures local deformation of a sample resulted from an applied stress or due to thermal energy by using micron-sized particles dispersed in a liquid [55]. The microrheological  
Figure 4: Scanning electron microscope images at low (400\(\times\)) and high (5000\(\times\)) magnifications of the control plain yogurt sample S1 (**A**,**C**) and symbiotic yogurt sample S3 with 0.5% _S. boulatdii_ + 1% inulin (**B**,**D**,**E**). properties of the symbiotic yogurt (S3) as compared to the control plain yogurt (S1) were studied, as shown in Figures 5-7. The MSD values of both the symbiotic yogurt (Figure 5A) and plain yogurt (Figure 5B) increased almost linearly with the decorrelation time, suggesting the viscous properties of both the yogurt samples. Similar linear increase in MSD values indicating the purely viscous characteristics of the whey protein concentrate when added from 40% to 80% oil was also reported [56]. However, the symbiotic yogurt due to addition of inulin exhibited a more viscous nature than the plain yogurt, as indicated by the shorter decorrelation time (1 s) of the former than that (10 s) of the latter reaching the MSD value of about 1000 nm\({}^{2}\). Changes of MSD values provided Brownian motion information in the yogurt samples [57]. The MSD slop value of less than 1 indicated that the motion of the particles or droplets is blocked; the value of 1 illustrating a Brownian motion type, and value of greater than 1 illustrating a ballistic motion type [58]. Figure 5: Mean square displacement (MSD) (**A** for S1, **B** for S3). Determination of the solid-liquid balance (SLB) values of the yogurt samples confirmed more solid properties of the symbiotic yogurt than the plain yogurt, since the former had higher SLB values (0.582\(\sim\)0.595) than the latter (0.503\(\sim\)0.518) (Figure 6). The SLB values above 0.50 indicated transformation from liquid domination to solid domination, while the SLB value of 0.5 was the critical value of a balanced state of liquid and solid [59]. Determination of the storage modulus (G\({}^{\prime}\)) and loss modulus (G\({}^{\prime\prime}\)) of the yogurt samples at the frequency range of 10\({}^{-3}\) to 10\({}^{2}\) Hz (Figure 7) showed that addition of inulin to yogurt slightly reduced the values of G\({}^{\prime}\) and G\({}^{\prime\prime}\), as reported by [PERSON] et al. [36] when starch was added in acid milk gels. Polysaccharides such as inulin had associative and segregative interactions with milk proteins [60; 61].