## 3 Results and Discussion
### Microbiological Properties of Kefir and Reconstituted Kefir Samples
Survivability reduction rate followed almost the same pattern for the rest of the samples prepared with kefir grains, and it was significantly lower, up to one logarithmic cycle, when compared to the CONTROL. The population of yeasts followed almost the same reduction rate for all kefir powder samples during the 45 day storage period (Figure 6c), indicating that their survival is governed mainly by their initial population. Neither the final fermentation pH nor the application of low-temperature treatment affected their viability loss, which was up to one logarithmic cycle. The unique symbiotic relationship that characterizes the variety of microorganisms present in kefir grains, the protective effect of kefiran, whose biosynthesis seems to be favored by low temperatures (results to be published soon), and the high fermentation pH (5.2) are responsible for increasing microbial viability during kefir powder storage (up to 45 days). According to [PERSON] et al. [17], spray drying produced with or without encapsulating matrices (maltodextrin and chemically modified starch with octenyl succinate) was the most efficient regarding the survival of lactic acid bacteria and yeast during 77 days of storage at 4 \({}^{\circ}\)C. However, at higher storage temperatures of 25 \({}^{\circ}\)C, the lactic acid bacteria population for all samples was significantly lower than those stored at 4 \({}^{\circ}\)C. The yeast populations decreased significantly and became undetectable after 14, 28, and 42 days, which is in accordance with the results of the present study. The authors attributed the reduced viability of yeasts to the absence of oxygen during storage. [PERSON] et al. [14] also suggested that the storage of kefir powder at refrigerated temperatures results in the population of lactic acid bacteria remaining stable for at least 60 days. Concerning yeasts, they did not preserve their viability after 40 days of storage under refrigerated temperatures. Since the viability of microorganisms during storage is affected by their initial numbers, the concentration of the carrier/encapsulation medium, the water activity, the storage temperature, the oxygen content, and the relative humidity during packaging [14] must be considered in order to improve kefir microorganism survival during storage. It is worth noting that the present study aimed at evaluating the microbial population during storage at ambient temperatures, since it is more cost effective. Figure 6: Microbial populations of lactococci (**a**) lactobacilli (**b**) and yeasts (**c**) of kefir powder samples as affected by storage time at ambient temperature for 15 and 45 days (CONTROL: sample prepared with commercial starter culture, without storage prior to drying; 4.4-0 and 5.2-0: samples prepared with kefir grains to final fermentation pH of 4.4 and 5.2, respectively, without storage prior to drying; and 4.4-7 and 5.2-7: samples prepared with kefir grains to final fermentation pH of 4.4 and 5.2, respectively, subjected to storage at 4 \({}^{\circ}\)C for 7 days). Vertical bars with no overlaps differ significantly.