3.3. Optimisation of the composition of the extraction solvents and the
extraction time
Assays were carried out using mixtures of methanol in water
between 50% and 20%. The results of these extractions are shown
in Fig. 3, where it can be seen that the conditions which produce
the best recovery for all the compounds, are those which use 40%
methanol in water. It must be noted here that, low differences
were found for glucosides, whereas for the acyl derivatives there
are appreciable differences between the recoveries found with
the different solvents. On the basis of these results, the percentage
of methanol in water was fixed at 40%.
As regards the determination of the time necessary for extraction,
the recovery of the eleven compounds was studied using
times between 2.5 and 30 min. The results are shown in Fig. 4. It
can be observed that there is a decrease in recovery when using
extraction times of 30 min, compared to the values obtained using
15 min. There were no significant differences found between 5 and 15 min and it was therefore decided to use 5 min as the extraction
time.