## 4 Conclusions  
Storage at refrigeration temperatures resulted in the increased moisture contents of the powder kefir samples, while it reduced the pH values for both the kefir and reconstituted kefir samples, regardless of the final fermentation pH. The white color intensity (brightness) of the kefir powder samples increased with increasing final fermentation pH (5.2), while the yellow color intensity increased by the low-temperature treatment. At low relative humidity environments (11.35-43%), all samples exhibited increased hygroscopicity when compared to the sample produced with commercial cultures. The samples prepared with kefir grains exhibited increased viability of lactococci and lactobacilli after spray drying and during storage up to 45 days. A final fermentation pH of 4.4, regardless of the application of low-temperature storage, favored lactococci survival after drying. On the other hand, low-temperature storage (4 \({}^{\circ}\)C for 7 days) of the fresh product before drying at a final fermentation pH of 4.4 favored lactobacilli survival. Increasing final fermentation pH (5.2), regardless of the application of low-temperature treatment, resulted in the utmost survival after drying for lactococci and lactobacilli. The population of yeasts was affected the least by the studied factors. During powder storage (bagged in multilayered laminate pouches with optimum moisture and oxygen barrier properties, under vacuum) at ambient conditions, the samples subjected to refrigerated storage with increased final fermentation pH values, exhibited the best results for the survival of lactococci, while for lactobacilli, an increased final fermentation pH (5.2) showed the most significant results. Based on the aforementioned, it is possible to accomplish desirable microbial populations for reconstituted kefir by regulating the microbial population of the fresh product, by the use of the appropriate starter cultures, allowing for increased final fermentation pH values or by applying low-temperature storage prior to drying the product. The presented study provides key insights with regard to some of the parameters that affect the production and storage of kefir powder. Kefir, a well known and extensively studied product, is a complex biological system with cross-linked interactions that considerably, in certain cases, differentiate its physical and functional characteristics. Understanding these interactions will confer considerable knowledge with regard to handling, improving the quality and making kefir easily accessible to consumers. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app15052509/s1](https://www.mdpi.com/article/10.3390/app15052509/s1)]([https://www.mdpi.com/article/10.3390/app15052509/s1](https://www.mdpi.com/article/10.3390/app15052509/s1)), Figure S1: Color parameters \(\mathsf{a}^{*}\) of powder kefir samples as affected by the fermentation pH and low-temperature treatment; Table S1: Mean values of moisture content and color parameters (\(\mathsf{L}^{*}\), \(\mathsf{a}^{*}\), \(\mathsf{b}^{*}\), WI-ASTM) of powder kefir samples, as well as pH values of reconstituted products during storage. Conceptualization, S.E., A.G., G.D. and E.P.K. ; methodology, S.E., A.G. and G.D.; software, D.G. and P.A. ; validation, D.G., S.E., A.G. and G.D.; formal analysis, P.A. and G.D.; investigation, S.E., P.A., O.G., D.G., A.G. and G.D.; resources, A.G. and G.D.; data curation, P.A. and D.G. ; writing--original draft preparation, S.E., A.G., D.G. and G.D.; writing--review and editing, S.E., A.G. and G.D.; visualization, S.E., A.G. and G.D.; supervision, S.E., A.G., E.P.K. and G.D.; project administration, S.E., A.G. and G.D.; funding acquisition, S.E. All authors have read and agreed to the published version of the manuscript. The research project was supported by the Hellenic Foundation for Research and Innovation (H.F.R.I.) under the \"2 nd Call for H.F.R.I. Research Projects to support Post-Doctoral Researchers\" (Project Number: 0075).