## 3 Results and Discussion
### Survivability under Simulated Gastrointestinal Conditions  
The survival of probiotics under gastrointestinal conditions represents a significant issue for their effectiveness, and microencapsulation could represent a valid method to provide significant protection [15]. The survival of free and encapsulated _S. thermophilus_ TH982 cells after 1, 2, and 3 h of incubation in simulated gastrointestinal conditions are presented in Figure 3. After 1 h of gastric fluid incubation, the highest reduction of viable cells was found, as expected, for free _S. thermophilus_ TH982, as the initial number of 10.40 \(\pm\) 0.10 log CFU/mL was diminished by 0.95 log CFU/mL. A notable decrease in viability after 3 h of gastrointestinal conditions was confirmed for free _S. thermophilus_ TH982 cells, reduced by approximately 1.60-log CFU/mL, dropping to 8.79 \(\pm\) 0.02 log CFU/mL. By contrast, for cells encapsulated with S alone, only 1.05 log CFU/g reduction of viable cells was observed, implying that microencapsulation provided protection compared to the free cells. This protection offered by sodium alginate might be related to the establishment of a hydrogel barrier through an external layer of sodium alginate that has retarded the permeation of simulated fluids into the capsules and thus the interaction with the probiotic cells [38]. Figure 2: Survivability of encapsulated and free _S. thermophilus_ TH982 cells during 21 days of storage in skimmed milk at 4 °C. S + G capsules showed low survivability during gastric environment; indeed, the reduction of viable cells was higher (0.52 log CFU/g decrease) than encapsulated cells with S + I (no reduction detected) after 1 h of gastric condition (pH 2.5). This fact might be due to a variation of pH, which changes the gelatin charge of amino and carboxyl groups so that the modification of cross-links and structure of the chain could influence the swelling behavior of gelatin capsules [39]. On the other side, an interesting outcome was given by the two types of prebiotics used as a co-encapsulating agent with sodium alginate. After 3 h of exposure to gastrointestinal conditions, S + I and S + F revealed the highest cell survivability without any significant difference, leading to a low cell reduction (less than 0.45 log CFU/g decrease for both agents). Prebiotics, such as 2\({}^{\prime}\)-FL and inulin, which could provide good protection and even promote cell proliferation, appeared to contribute to the growth of _S. thermophilus_ TH982. In addition, oligosaccharides are difficult to decompose by enzymes in digestive fluid but can be metabolized by beneficial bacteria in the colon [30]. It has been further demonstrated that oligosaccharides contained in human milk have an extraordinary resistance to hydrolysis by digestive enzymes of the small intestine [40]. The combination of calcium alginate with prebiotics such as inulin improves the viability of probiotics and facilitates the formation of an integrated structure of capsules. Researchers found better protection of _Lactobacillus casei_ and _Bifidobacterium bifidum_ cells in coated capsules with prebiotics such as inulin after the gastrointestinal transit. The addition of prebiotics could be synergistic in gelling, and as a result, may help to maintain and improve the degree of protection of the bacterial cells [41]. Lastly, the free cell suffered more from the gastric conditions than that during the 3-h gastrointestinal transition. In contrast, encapsulated bacteria evidenced greater reductions during gastrointestinal transit than under gastric conditions alone. This behavior may be due to the fact that alginate is stable in low-pH solutions: the ionotropic alginate gel formed by Ca\({}^{2+}\) cross-linking of carboxylate groups is insoluble at low pH, but exposure to neutral pH or higher solubilize the alginate, causing swelling [42]. Figure 3: Survivability of encapsulated and free _S. thermophilus_ TH982 cells during exposure to simulated gastrointestinal conditions.