# Quality Assessment of Organic Kefirs Made with Kefir Grains and Freeze-Dried Starter Cultures
## 3 Results and Discussion
### Analysis of Organic Kefirs During Refrigerated Storage  
#### 3.3.1 Physicochemical Parameters  
The results of active acidity (pH) and titratable acidity (% of lactic acid) measured over 21 storage days are presented in Table 2. The value of both types of acidity depended on the type of kefir and the storage time (Table 1). Throughout the storage period, kefir G24 had the lowest pH values, followed by G12. Kefirs made with freeze-dried culture (L12 and L24) had significantly higher (\(p\) < 0.05) pH values, indicating the lower acidification capacity of this culture compared to traditional kefir grains. According to CA _Standard for Fermented Milks_(2017), the titratable acidity of kefir cannot be lower than 0.6% of lactic acid, and all the kefirs met this standard throughout the storage period. [PERSON] et al. (2018) also found lower pH values in cow milk-based kefir made with KGs compared with kefir made with freeze-dried cultures. The acidification ability of the kefir starter culture is determined not only by the type of culture but also by the quantitative proportion of individual microorganisms, the size of the inoculum, as well as the temperature and duration of the process and agitation during fermentation ([PERSON] et al., 2018; [PERSON] et al., 2018). The results for kefir G24 were in agreement with the findings of [PERSON] et al. (2018), who reported pH values in the range of 4.3-4.5 for kefirs obtained with KG supplementation during 3-week refrigerated storage. Lower values of pH (belowpH 4) in kefirs produced with KGs were reported by [PERSON] and [PERSON] [63], and [PERSON] et al. [64]. Regarding titratable acidity, kefir G24 had the highest lactic acid content (Table 2). During storage, an increase in lactic acid content was observed only in kefir L12. The stability of titratable acidity in kefirs during refrigerated storage is related to the presence of yeast, which slows the proliferation of lactic acid bacteria, resulting in the production of small amounts of lactic acid [46; 61]. The lactic acid content in kefir G24 was consistent with the findings of [PERSON] et al. [62] for kefir obtained with the addition of 2% KG and fermented at 28 \({}^{\circ}\)C for 20 h (0.88-0.91%). The study showed that the water content for experimental kefirs presented similar values to that observed in milk and oscillated around 88-90% (Table 2). The water content of kefirs was stable over the duration of the experiment. Significant differences (\(p<0.05\)) between the variants were recorded only on day 1. A similar range of water content in kefirs was reported in a study by [PERSON] and [PERSON] [65] (86.87-89.84%) and [PERSON] et al. (2003) [46]. A higher range of water content in kefir obtained with KG supplementation, ranging from 90.30 to 90.75% was reported by [PERSON] and [PERSON] [63]. Similarly to our study, the lack of differences in water content in kefir with a freeze-dried culture and a traditional culture was found by [PERSON] et al. [30], who noted the value of this indicator in a range between 88.7 and 89.2%. The analysis of SI conducted by the centrifuge method indicated quite large discrepancies among the samples. The value of this parameter was significantly affected by both  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Day** & **L12** & **L2  
storage time and the type of kefir (Table 2). Throughout the storage period, kefir L24 had the lowest index for syneresis, and kefir G12 had the highest. The SI of kefirs G12 and G24 increased during storage time. Only in the case of kefir L24 did the SI remain unchanged throughout storage. The lower water binding capacity of kefir produced with KGs compared with kefir made with a freeze-dried culture is associated with KG filtration. This process alters the structure of the curd, reducing its ability to hold water [52]. In a study conducted by [PERSON] [66], the susceptibility to syneresis of kefirs from conventional milk stored for 28 days ranged from 19.54% to 40.00%.