# Extraction of Galactolipids from Waste By-Products:
## 3 Results and Discussion
### Ultrasound-Assisted Extraction (UAE)  
The experiments on the possible use of UAE in the isolation of galactolipids began with the evaluation of twelve commonly used solvents of various polarities. The rosehip pomace was mixed with them in a ratio of 1:10 (\(m/v\)) and subsequently extracted in two variants: with and without sonication. The yields of MGDGs obtained are listed in Table 4.  
Apart from the most and the least polar (water and hexane, respectively), all the solvents were able to extract MGDGs to some extent. The best results were obtained for chlorinated hydrocarbons, yet even dichloromethane, which is much safer for people and the environment than chloroform, can be hardly considered a green solvent. Therefore, the solvent characterized by a lower extraction efficiency, but of lesser environmental and health impact, must be chosen. Ethanol combines low toxicity with a low cost; thus it was chosen for the further experiments. Additionally, its use as a cosolvent during SFE allows a systematic comparison of these two techniques. The sonication made it possible to significantly increase the yield of extraction in all the solvents evaluated, which indicated the potential of the technique. The next part of the experiments was the investigation of the impact of the sonication time and ratio of pomace and ethanol on the efficiency of the extraction--the results are presented in Figure 2. Two solid-liquid ratios and three sonication times were investigated. The control samples were extracted with ethanol for the same amount of time without any means of a process intensification. As was stated before, the samples were shaken for 1 min prior to removal of the solvent. The amphiphilic character of galactolipids was visible during the selection of the appropriate solvent. Both highly polar (water) and non-polar (hexane) solvents were unsuitable for the extraction. The impact of the sonication time on the yield presented in Figure 2 is in accordance with the extraction curves reported by other authors [26; 27; 28]. Sonication leads to the disintegration of cells on the surface of the matrix particles, which at the beginning of the process leads to a significant increase in yield, although longer treatment does not have such an effect, as the majority of the cells are already broken. The comparison of the extraction curves suggests that differences between the sonicated and the control samples are mainly the result of improvement of the mass transfer. The bigger gap between sonicated and control yields in the case of 1:25 ratio is supposedly the result of a limited solubility of galactolipids in ethanol. The sonication of the rosehip samples led to a substantial improvement in the yields obtained (up to 74%) with a relatively low cost \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Solvent** & **Relative Polarity [25]** & **Sonicated** & **Control** \\ \hline hexane & 0.009 & \(\leq\)0.1 a & \(\leq\)0.1 a \\ toluene * & 0.099 & 2.2 \(\pm\) 0.3 b & 1.5 \(\pm\) 0.2 \\ methyl t-butyl ether * & 0.124 & 8.5 \(\pm\) 0.5 d & 7.2 \(\pm\) 0.2 \\ ethyl acetate * & 0.228 & 11.5 \(\pm\) 0.8 e & 9.5 \(\pm\) 0.4 \\ chloroform * & 0.265 & 34.1 \(\pm\) 1.6 h & 28.6 \(\pm\) 0.7 \\ dichloromethane * & 0.309 & 32.9 \(\pm\) 1.0 h & 27.8 \(\pm\) 0.5 \\ acetone * & 0.355 & 14.3 \(\pm\) 0.1 f & 11.7 \(\pm\) 0.6 \\ acetonitrile * & 0.460 & 9.0 \(\pm\) 0.4 d & 7.1 \(\pm\) 0.3 \\ isopropanol * & 0.546 & 7.2 \(\pm\) 0.1 c & 6.2 \(\pm\) 0.3 \\ ethanol * & 0.654 & 15.2 \(\pm\) 0.4 g & 13.0 \(\pm\) 0.2 \\ methanol * & 0.762 & 14.6 \(\pm\) 0.7 g & 11.9 \(\pm\) 0.6 \\ water & 1.000 & \(\leq\)0.1 a & \(\leq\)0.1 a \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Impact of sonication on the efficiency of MGDG extraction from rosehip pomace using various solvents. All yields in mg per kg of pomace; sonication time was 5 min. An asterisk next to the solvent name denotes a significant difference between sonicated and control samples, while letters stand for differences between solvents (both at \(p\leq\) 0.05). of implementation.