**4. Conclusions**

The recommended HP conditions in the literature (200 MPa at 20−25 ◦C for process time for up to 10−15 min) for texture improvement in dairy products was found not detrimental to the viability of the examined probiotic bacteria. In the case of model systems, the maximum calculated inactivation due to HP process was about 0.4 log10 CFU/mL. To describe the effect of pressure and temperature process conditions on the viability of the tested probiotic bacteria, a single multi-parameter equation was proposed, and the parameters of this model were estimated for the most baro-sensitive probiotic bacterium (i.e., *Bifibobacterium bifidum*). When HP processing was applied in probiotic yoghurt at the final stage of production, especially when treated at 200−300 MPa, the quality and sensorial properties of the final product were improved. The viscosity of the final product increased and the whey separation decreased, while the viability loss of the probiotic microorganisms ranged between 0.5−1.2 log10 CFU/g, and no significant viability loss was observed during refrigerated storage for 28 days. Overall, HP process can be successfully applied in such dairy products at the final step of production in order to improve their quality attributes and extend their shelf life without the need for stabilizer addition, while acceptably affecting their functionality. Moreover, the addition of flavor enhancement substances seems to improve the rheological properties of the coagulum but also increase the viability of the probiotic bacteria. Further research could focus on the effect of the addition of prebiotics in similar treated dairy products both on probiotics viability and their quality indices.

**Author Contributions:** Conceptualization, M.T. and P.T.; methodology, M.T. and C.S.; validation, M.T. and C.S.; formal analysis, M.T., C.S. and M.O.-R.; investigation, M.T., M.O.-R. and C.S.; writing—original draft preparation, M.T. and C.S.; visualization, M.T. and C.S.; supervision, M.T. and P.T.; project administration, P.T. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was co-funded by STATE SCHOLARSHIPS FOUNDATION of Greece, in the context of Dr Maria's Tsevdou PhD Scholarship Grant (Food Engineering, 0840620729.006.031).

**Acknowledgments:** The authors would like to kindly thank Christian–Hansen Hellas for the gift of *Bifidobacterium lactis* BB12 and *Lactobacillus acidophilus* LA5 probiotic cultures.

**Conflicts of Interest:** The authors declare no conflict of interest.
