## 3 Results and Discussion
### Rheological Properties Analysis of Set Yoghurt  
The apparent viscosity changes in set yoghurt containing different RE concentrations with different shear rates are shown in Figure 3a. A negative correlation between viscosity and the shear rate was observed, indicating that the set yoghurt exhibited a non-Newtonian shear thinning behaviour due to the breaking of protein bonds [38]. In particular, the apparent viscosity of set yoghurt showed an upward trend with increasing RE concentrations, demonstrating that RE had a significant impact on the apparent viscosity of set yoghurt. The most likely explanation for this phenomenon was attributed to the formation of a strong network due to the interaction of polysaccharides with casein micelles [39], as well as the increase in WHC in the set yoghurt. Viscosity affected the texture, mouthfleel, and acceptability of the set yoghurt significantly; higher viscosity indicated better texture, flavour, and acceptability by the consumers [40]. These results were consistent with the aforementioned studies of set yoghurt texture.  
Figure 3: Rheological properties of different set yoghurt samples stored for 24 h in a low-temperature condition. (**a**) Apparent viscosity of set yoghurt; (**b**) storage modulus (G\({}^{\prime}\)) and loss modulus (G\({}^{\prime\prime}\)) of set yoghurt; (**c**) loss tangent (tan \(\delta\)) of set yoghurt.  
The variation in the G\({}^{\prime}\) and G\({}^{\prime\prime}\) of the set yoghurt containing different RE concentrations with frequency was explored. As shown in Figure 3b, the values of G\({}^{\prime}\) and G\({}^{\prime\prime}\) increased with frequency in the entire range of the test frequency in all samples; meanwhile, G\({}^{\prime}\) values were always higher than G\({}^{\prime\prime}\), which indicated that the yoghurt system showed a solid-like behaviour. Interestingly, the values of G\({}^{\prime}\) and G\({}^{\prime\prime}\) in the set yoghurt supplemented with RE were higher than those of the control and exhibited an upward trend with increasing RE concentrations, which suggested that RE could improve the hardness of the set yoghurt with a reasonable explanation that the polymer entanglement in the solid-like gel increased significantly [41]. The good viscoelastic gel structure of the set yoghurt with the addition of RE was consistent with the results obtained by the WHC, apparent viscosity, and texture profile analysis. A similar result was reported by a previous study where the increase in guar gum concentrations increased the complex viscosity of yoghurt [42].  
The value of \(\tan\delta\) as a function of frequency was subsequently analyzed. As can be seen in Figure 3c, all the \(\tan\delta\) values of the set yoghurt samples were less than one after 24 h of low-temperature storage, which indicated that the set yoghurts showed solid-like behaviour due to the higher G\({}^{\prime}\) values and lower G\({}^{\prime\prime}\) values [43]. With the increase in RE concentrations, the \(\tan\delta\) value exhibited a downward trend, and a similar result was also reported by investigations of _Tremella ficiformis_ polysaccharides [41]. Additionally, the \(\tan\delta\) values of the set yoghurt samples showed an upward trend with the frequency, which was consistent with previous exopolysaccharides(cEPS and fEPS) studies and contrary to the reports of _Potentilla anserine_ and _Lactobacillus helveticus_ MB2-1 polysaccharides [44; 45; 46], although both the \(\tan\delta\) values of yoghurts in the three experiments were less than one. It has been reported that the set yoghurt with a lower \(\tan\delta\) value possessed the properties of difficult dehydration [46]. Consequently, the addition of RE improved the stability of the set yoghurt.