## 3 Results and Discussion
### Physicochemical Properties of Powder and Reconstituted Kefir Samples
Similar results were reported in our previous study [20], in contrast to [PERSON] and [PERSON] [12] who reported no differences between kefir samples and their corresponding reconstituted ones. Color is an important factor affecting the quality of foods and their acceptance by consumers. Given that fresh kefir is characterized by increased white color intensity, the production of kefir powder with increased brightness and WI-ASTM, as well as reduced yellow color intensity, is desirable. The white color of milk and dairy products is due to the scattering of light from the casein micelles and fat globules. The white color intensity of milk is increased further from whey protein denaturation due to the thermal treatment applied to milk before inoculation with the starter culture. Why proteins form complexes with caseins, increasing the scattering of light and white color intensity [31]. On the other hand, carotenoids, that are responsible for the yellow color of fat [31], are indiscernible when fat is found at low concentrations, such as in the kefir of semi-skimmed milk. Taking into account the aforementioned, kefir is characterized by increased white color intensity (brightness) and no visible yellowness. According to statistical analysis and as can be seen in Figure 3, the L*, b*, and WI-ASTM color components of the kefir powder changed significantly among the samples (\(p<0.05\)). Figure 2: pH values of reconstituted kefir samples as affected by fermentation pH and low-temperature treatment (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. Color parameter a* did not exhibit statistically significant variations (Supplementary File, Figure S1). It ranged between \(-0.885\) and \(-0.475\) (\(-0.475\) CONTROL sample) and the negative values observed (green color intensity) are due to the riboflavin presence in the milk used [31]. Similar or lower values for a* were reported in the relevant literature (\(-2.94\) to \(-0.77\)) [12; 13; 16; 17]. The L* values for the keir powder samples ranged between 97.7 and 98.9 (97.9 CONTROL sample), which is noticeably higher when compared to the ones cited in the literature for keir powder produced by spray drying (84.01 to 90.6, [12]; 95.96, [13]; 90; 91; 93.29-95.53, [17]). The sample that exhibited the highest statistically significant value for brightness was the one with the highest fermentation pH that was not subjected to low-temperature storage (5.2-0). As mentioned earlier, the white color of dairy products is due to the scattering of light between the fat globules and the casein micelles as the prevailing macromolecule constituents of milk. The bigger the size and number of fat globules and casein micelles, the greater the white color intensity of the samples [31]. When casein micelles are at conditions far from their isoelectric point (4.6), they show increased voluminosity due to the increased repulsive forces between protein molecules, resulting in augmented light scattering and thus increased brightness. Color parameter b* varied between 5.54 and 7.43 (5.54 for the CONTROL), which was among the lowest reported in the literature (8.62-14.64, [12]; 8.18, [13]; 4.7-7.3, [16]; 3.89-8.12, [17]).