## 3 Results and Discussion
### Effect of the Process Parameters on Triterpene Acids Content  
Table 3 shows the concentration of betulinic, oleanolic and unsolic acid in the heather and marigold extracts. In the case of heather, the use of the co-solvent (Run E2 and E3-2) promoted the extraction of the three acids (Run E2 and E3-2), mainly oleanolic acid, despite unsolic acid being the largest quantity of triterpene acid in heather. This effect was also observed by [PERSON] et al. [13]. A possible explanation can be formulated considering the solubility of these compounds. To our knowledge, no solubility data of these acids in SCCO\({}_{2}\) has been reported. Nevertheless, the solubility of oleanolic acid in ethanol is higher in comparison with unsolic acid [29]. In the case of the unsolic acid, the highest concentration in the heather extracts was obtained by fractionating at 50 MPa (Run E1-S1). Pressure above 30 MPa was necessary for the efficient extraction and concentration of this compound without using a co-solvent. Unlike heather, the use of a co-solvent did not increase the concentration of the triterpene acids in the marigold extracts. The highest concentrations were obtained when pure SCCO\({}_{2}\) was used, reaching extracts with high concentration of these compounds at 30 MPa. The main triterpene acid obtained was oleanolic acid regardless of the use of co-solvent, whereas betulinic acid was only obtained in heather extracts. This finding agrees with the finding reported by [PERSON] et al. [13]. Table 4 shows the concentration of the triterpene acid in the extracts obtained from the combined heather + marigold extraction. Unlike the extraction of each plant individually, the combined extraction produced extracts with concentrations of unsolic acid higher than oleanolic acid (experimental values). Furthermore, considering the theoretical values of concentration for each compound and operation \begin{table}
\begin{tabular}{c c c c c} \hline  & **Heather** & **Marigold** & **Heather + Marigold (50:50)** \\ \hline
**Run** & **Experimental** & **Experimental** & **Experimental** & **Theoretical** \\ \hline E1-S1 & 0.26 & 0.33 & 0.49 & 0.30 \\ E1-S2 & 1.94 & 3.04 & 2.64 & 2.49 \\ E2 & 1.71  & 6.94  & 6.06  & 4.33 \\ E3-1 & 2.65 & 2.76 & 2.04 & 2.71 \\ E3-2 & 5.28 & 4.48 & 3.43 & 4.88 \\ \hline \end{tabular} Notes:  
Mean value between duplicate experiments. The coefficient of variation obtained was 7.0%, 9.4% and 6.3% for heather, marigold and heather + marigold, respectively.  
\end{table} 
Table 2: Overall extraction yield (mass of extract/mass of plant \(\times\) 100) obtained from SFE of heather, marigold and combined heather + marigold (50:50) extraction. Theoretical extraction yields are expressed as the arithmetic mean of the experimental extraction yield obtained from each individual plant. \begin{table}
\begin{tabular}{c c c c c c} \hline  & & **Heather** & & **Marigold ** \\ \hline
**Run** & **Oleanolic** & **Unsolic** & **Betulinic** & **Oleanolic** & **Unsolic** \\ \hline E1-S1 & 13.50 \(\pm\) 1.65 & 98.56 \(\pm\) 10.20 & 3.89 \(\pm\) 0.37 & 36.79 \(\pm\) 3.87 & 19.46 \(\pm\) 1.20 \\ E1-S2 & 2.53 \(\pm\) 0.22 & 2.95 \(\pm\) 0.05 & 3.29 \(\pm\) 0.21 & 42.96 \(\pm\) 2.44 & 22.79 \(\pm\) 1.98 \\ E2 & 54.04 \(\pm\) 3.21 & 38.67 \(\pm\) 1.23 & 17.78 \(\pm\) 1.58 & 29.90 \(\pm\) 1.25 & 15.54 \(\pm\) 1.33 \\ E3-1 & 1.44 \(\pm\) 0.15 & 2.19 \(\pm\) 0.10 & 2.11 \(\pm\) 0.39 & 59.96 \(\pm\) 1.08 & 30.80 \(\pm\) 0.90 \\ E3-2 & 73.14 \(\pm\) 2.87 & 51.62 \(\pm\) 1.52 & 28.13 \(\pm\) 3.10 & 8.97 \(\pm\) 0.87 & 3.59 \(\pm\) 0.35 \\ \hline \end{tabular} Notes:  
A amount of betulinic acid in marigold extracts below quantification limit.  
\end{table} 
Table 3: Concentration (mg/g extract) of oleanolic, unsolic and betulinic acid in heather and marigold extracts obtained by SFE.