# Traditional Grain-Based vs. Commercial Milk Refirs, How Different Are They?
## 3 Results and Discussion
### Targeted Metabolites Analysis
Similar to lactose hydrolyzing activity, it was shown that the appli  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & **Fermen-Tation** & **Lactose** & **Glucose** & **Galactose** & **Lactate** & **Acetate** & **Glycerol** \\  & **Time (h)** & **(g L\({}^{-1}\))** & **(mg L\({}^{-1}\))** & **(mg L\({}^{-1}\))** & **(g L\({}^{-1}\))** & **(mg L\({}^{-1}\))** & **(mg L\({}^{-1}\))** & **(mg L\({}^{-1}\))** \\ \hline PN1 & 23 \(\pm\) 1 & 33.6 \(\pm\) 5.7 \({}^{\text{ab}}\) & 133.3 \(\pm\) 82.6 \({}^{\text{ab}}\) & 149.3 \(\pm\) 58.0 \({}^{\text{bc}}\) & 1.7 \(\pm\) 1.1 \({}^{\text{c}}\) & 328.4 \(\pm\) 60.5 \({}^{\text{c}}\) & 297.7 \(\pm\)58.4 \({}^{\text{b}}\) \\  & 47 \(\pm\) 1 & 9.2 \(\pm\) 5.4 \({}^{\text{c}}\) & 25.1 \(\pm\) 3.6 \({}^{\text{a}}\) & 23.2 \(\pm\) 8.7 \({}^{\text{d}}\) & 3.2 \(\pm\) 0.1 \({}^{\text{b}}\) & 778.8 \(\pm\) 68.8 \({}^{\text{a}}\) & 682.2 \(\pm\)95.7 \({}^{\text{c}}\) \\ PN2 & 23 \(\pm\) 1 & 37.2 \(\pm\) 2.0 \({}^{\text{a}}\) & 197.2 \(\pm\) 52.8 \({}^{\text{b}}\) & 266.3 \(\pm\) 35.5 \({}^{\text{b}}\) & 1.7 \(\pm\) 0.3 \({}^{\text{c}}\) & 459.5 \(\pm\) 29.8 \({}^{\text{b}}\) & 232.0 \(\pm\)30.0 \({}^{\text{b}}\) \\  & 47 \(\pm\) 1 & 15.3 \(\pm\) 3.4 \({}^{\text{c}}\) & 29.6 \(\pm\) 0.5 \({}^{\text{a}}\) & 21.8 \(\pm\) 10.2 \({}^{\text{d}}\) & 3.9 \(\pm\) 0.4 \({}^{\text{b}}\) & 944.5 \(\pm\) 15.2 \({}^{\text{a}}\) & 538.1 \(\pm\)76.1 \({}^{\text{c}}\) \\ PN3 & 23 \(\pm\) 1 & 37.6 \(\pm\) 2.8 \({}^{\text{a}}\) & 176.5 \(\pm\) 74.0 \({}^{\text{b}}\) & 368.8 \(\pm\) 112.5 \({}^{\text{b}}\) & 1.2 \(\pm\) 0.2 \({}^{\text{c}}\) & 300.2 \(\pm\) 21.8 \({}^{\text{c}}\) & 253.9 \(\pm\)20.1 \({}^{\text{b}}\) \\  & 47 \(\pm\) 1 & 14.1 \(\pm\) 1.7 \({}^{\text{c}}\) & 27.0 \(\pm\) 4.2 \({}^{\text{a}}\) & 12.6 \(\pm\) 1.7 \({}^{\text{d}}\) & 3.3 \(\pm\) 0.6 \({}^{\text{b}}\) & 846.9 \(\pm\) 58.2 \({}^{\text{a}}\) & 639.4 \(\pm\)37.2 \({}^{\text{c}}\) \\ FN & 23 \(\pm\) 1 & 40.3 \(\pm\) 2.0 \({}^{\text{a}}\) & 203.5 \(\pm\) 76.9 \({}^{\text{b}}\) & 228.7 \(\pm\) 61.4 \({}^{\text{b}}\) & 1.3 \(\pm\) 0.1 \({}^{\text{c}}\) & 372.8 \(\pm\) 82.3 \({}^{\text{b}}\) & 191.0 \(\pm\)56.9 \({}^{\text{b}}\) \\  & 47 \(\pm\) 1 & 37.6 \(\pm\) 5.3 \({}^{\text{a}}  
cation of mixed-cultures compared to mono-cultures leads to lower galactose contents in fermented milk [39]. The organic acid profile of the fermented milks is the result of both anabolic and catabolic processes. Lactic acid is the main end product of the main carbohydrate metabolism in LAB, although quantities of other organic acids such as acetate, butyrate and propionate are produced, especially by heterofermative LAB. At both time points, 23 \(\pm\) 1 and 47 \(\pm\) 1 h, the lactate concentrations were significantly lower (\(p\) < 0.05) in traditional kefirs compared to commercial kefirs. This can be explained by the consumption of lactate by yeast species [2]. Lactate concentration in commercial kefir samples was about two times higher than in traditional kefirs and the concentrations were in the range previously reported for commercial kefir [42; 43]. Similar to lactate, the concentration of acetate increased over time in traditional kefirs. The amount of acetate in three commercial kefirs was between 584.4 \(\pm\) 105.6 and 810.1 \(\pm\) 84.6 mg L\({}^{-1}\), which is well in agreement with [PERSON] et al. [42] as well as the amounts that were reported as side product from cultures of _L. lactis_ subsp. _Lactis_ biovar _diacetylalctis_[44]. Glycerol concentration was observed to be significantly higher (\(p\) < 0.05) in traditional kefirs compared to commercial kefirs, which indicates considerable activities of yeast species in traditional kefirs. Among them, traditional kefir LS was exceptional, with a significantly lower glycerol concentration, which is probably due to a lower enzyme provision for this conversion by _Kz. unispora_, though there is no previous report on this yeast regarding to this observation.