The major components in the extract from leaves are cuticular waxes. The equilibrium extraction curves measured for oleoresin (total extract) from stinging nettle leaves in this work are compared in Figure 51 with equilibrium extraction curves for cuticular waxes from peppermint leaves at similar operating conditions. It is evident that the slopes of the stinging nettle curves are practically identical with those measured for peppermint waxes, except for the short initial section of fast extraction of a compound that is present in nettle leaves in the concentration of 0.35 g/100 g matrix. The compound is very probably fatty oil, whose CO2 extraction from stinging nettle leaves. Figure 3 shows also the yields from freshly ground stinging nettle leaves that are increased by volatile compounds, missing in the ground leaves after several months of storage.

In the examined range of temperatures and pressures the slopes of oleoresin extraction curves varied only slightly, increasing with increasing temperature and to a smaller extent with increasing pressure. When ethanol was added to the solvent, the total extraction yield was higher due to co-extracted polar compounds, but the shape of extraction curves remained unchanged.

Figure 51 : Extraction from leaves with pure CO2 at 40 °C.

Oleoresin from stinging netle leaves, 28 MPa, this work: (<) 0 % ethanol; (u) 4.3 % ethanol; (l) initial experiment with the leaves containing volatile compounds, 4.3 % ethanol; (——) fitted curves. Waxes from peppermint leaves, pure CO2 [2]: (´) 24.5 MPa; (ê) 30 MPa; (----) fitted curves.