## 3 Results and Discussion
### Choice of Working Conditions for Future Application in the Dairy Production  
Figure 5 presents the relationship between the permeate flux and energy demand at different working conditions (transmembrane pressure and VRR). The working field was separated into four quadrants with different combinations of permeate flux and energy demand. The most desirable quadrant with the most efficient conditions was this where the permeate flux is maximal and the energy is minimal. In this quadrant, there are four \begin{table}
\begin{tabular}{l c c c c} \hline \hline
**Phospholipids, mg/100 g** & **Initial Buttermilk** & \begin{tabular}{c} **Retentate at** \\ **VRR 2** \\ \end{tabular} & \begin{tabular}{c} **Retentate at** \\ **VRR 3** \\ \end{tabular} & \
\begin{tabular}{c} **Retentate at** \\ **VRR 4** \\ \end{tabular} &
\begin{tabular}{c} **Retentate at** \\ **VRR 5** \\ \end{tabular} \\ \hline Lysophosphatidylethanolamine & 2.6 \(\pm\) 0.2 \({}^{\text{a}}\) & 9.5 \(\pm\) 0.4 \({}^{\text{b}}\) & 9.8 \(\pm\) 0.6 \({}^{\text{b}}\) & 11.0 \(\pm\) 0.5 \({}^{\text{c}}\) & 11.5 \(\pm\) 0.4 \({}^{\text{c}}\) \\ Lysophosphatidylcholine & 3.9 \(\pm\) 0.1 \({}^{\text{a}}\) & 8.3 \(\pm\) 0.2 \({}^{\text{b}}\) & 8.7 \(\pm\) 0.6 \({}^{\text{b}}\) & 9.1 \(\pm\) 0.3 \({}^{\text{b}}\) & 10.0 \(\pm\) 0.2 \({}^{\text{c}}\) \\ Phosphatidylserine & 8.4 \(\pm\) 0.2 \({}^{\text{a}}\) & 22.6 \(\pm\) 0.9 \({}^{\text{b}}\) & 23.0 \(\pm\) 0.3 \({}^{\text{b}}\) & 25.0 \(\pm\) 0.6 \({}^{\text{c}}\) & 26.5 \(\pm\) 0.5 \({}^{\text{d}}\) \\ Phosphatidylinositol & 23.1 \(\pm\) 0.5 \({}^{\text{a}}\) & 35.9 \(\pm\) 0.7 \({}^{\text{b}}\) & 67.3 \(\pm\) 0.6 \({}^{\text{c}}\) & 71.0 \(\pm\) 0.9 \({}^{\text{d}}\) & 73.5 \(\pm\) 1.0 \({}^{\text{e}}\) \\ Phosphatidylcholine & 26.7 \(\pm\) 0.5 \({}^{\text{a}}\) & 47.5 \(\pm\) 1.3 \({}^{\text{b}}\) & 69.6 \(\pm\) 1.8 \({}^{\text{c}}\) & 72.1 \(\pm\) 1.2 \({}^{\text{d}}\) & 74.2 \(\pm\) 1.4 \({}^{\text{d}}\) \\ Sphingomyelin & 17.1 \(\pm\) 0.2 \({}^{\text{a}}\) & 18.6 \(\pm\) 0.4 \({}^{\text{b}}\) & 31.6 \(\pm\) 1.2 \({}^{\text{c}}\) & 41.0 \(\pm\) 1.0 \({}^{\text{d}}\) & 46.1 \(\pm\) 0.4 \({}^{\text{e}}\) \\ Phosphatidylethanolamine & 28.5 \(\pm\) 0.6 \({}^{\text{a}}\) & 63.0 \(\pm\) 0.7 \({}^{\text{b}}\) & 70.0 \(\pm\) 1.5 \({}^{\text{c}}\) & 78.0 \(\pm\) 0.6 \({}^{\text{d}}\) & 80.6 \(\pm\) 0.4 \({}^{\text{e}}\) \\ Diphosphatidylglycerol & 4.4 \(\pm\) 0.2 \({}^{\text{a}}\) & 5.7 \(\pm\) 0.2 \({}^{\text{b}}\) & 6.6 \(\pm\) 0.6 \({}^{\text{c}}\) & 7.1 \(\pm\) 0.2 \({}^{\text{c}}\) & 8.1 \(\pm\) 0.3 \({}^{\text{d}}\) \\ Phosphatidic acids & 7.8 \(\pm\) 0.2 \({}^{\text{a}}\) & 8.5 \(\pm\) 0.5 \({}^{\text{a}}\) & 9.9 \(\pm\) 0.6 \({}^{\text{b}}\) & 11.1 \(\pm\) 0.3 \({}^{\text{c}}\) & 11.7 \(\pm\) 0.5 \({}^{\text{c}}\) \\ Total phospholipids & 123 \(\pm\) 3 \({}^{\text{a}}\) & 220 \(\pm\) 5 \({}^{\text{b}}\) & 296 \(\pm\) 8 \({}^{\text{c}}\) & 325 \(\pm\) 7 \({}^{\text{d}}\) & 342 \(\pm\) 8 \({}^{\text{e}}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Phospholipid composition of buttermilk retentates. \begin{table}
\begin{tabular}{l c c} \hline \hline
**Component** & **Linear Model** & **Correlation Coefficient R** \\ \hline Proteins & P = 0.4108 \(\times\) VRR + 0.8768 & 0.984 \\ Fat & F = 1.0133 \(\times\) VRR \(-\) 0.1467 & 0.999 \\ Ash & A = 0.3284 \(\times\) VRR + 0.9295 & 0.996 \\ Dry matter & DM = 0.381 \(\times\) VRR + 1.1571 & 0.999 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Linear models for concentration factor of buttermilk compounds depending on the volume reduction ratio. experimental points corresponding to these criteria. Two of them concern VRR 1, i.e., the beginning of the ultrafiltration process where there is no concentration of the sweet buttermilk. The two others concern VRR 3. Between them, it is more suitable to choose the point which concerns 0.2 MPa and VRR 3 because here the energy is 2.32 times lower than at the point concerning 0.5 MPa and VRR 3.