Factors influencing the yield of essential oil content from Eucalyptus globulus leaves grown in Southern Ethiopia
Fikremariam Haile, Yosef Melka, Yohannes Fekadu and Zewdinesh Damtew
This study aims to investigate the effect of three experimental factors such as harvesting seasons (dry season, long rain and short rain seasons), leave types (immature twin leaves, matured but lignified leaves and matured leaves) and leaves position ( top, medium and bottom) on moisture content (MC), essential oil content (EOC) and essential oil yield (EOY) from Eucalyptus globulus leaves. This experiment was conducted to determine MC, EOC and EOY, which are expressed by percent on moisture content and essential oil content, while gm/tree on essential oil yield on the basis of dry leaf weight. The oil was obtained by hydro distillation of E. globulus leaves using Clevenger apparatus for 3 hrs. Except, EOC, EOY and optical rotation (O.R), the main effect of harvesting season (HS) significantly (p<0.05) influenced MC, refractive index (RI) and specific gravity (SG) of E. globulus leaf oil. The effect of leaf position (LP) and leaf type (LT) on all parameters considered in the experiment, vis. MC, EOC and EOY were also significant except EOY in LP. When the interaction effect between (HS*LP), (HS*LT) and (LP*LT) were observed, it has not significantly influenced all parameter measured except EOY at the interaction effect between (HS*LT) and (LP*LT). In the experiment, the main effects of all factors, higher MC was recorded for HS 53.96% on dry season (DS), for LP 54.48% on top position and for LT 58.5% on immature twin leaves and least moisture content was recorded for matured and lignified leaves (ML) (50.14%) on LT. The main effect of leaf position showed significantly (p<0.01) higher EOC (23.67%) at top leaf position than at bottom leaf position and 10.25% at top leaf position than medium leaf position. The main effect of leaf type showed significantly (p<0.01) higher EOC ( 13.28%) at immature twin leaves than at matured and lignified leaves and 8.86% at immature twin leaves than at matured leaf type. The interaction effect between harvesting season and leaf type showed a significantly higher EOY for matured but lignified leaves (28.74%) at long rain session, which was followed by matured leaves (21.5%) at short rain season. Comparing the interaction effect between leaf position and leaf type, the maximum essential oil yield was recorded with parallel statistical significance for matured but lignified leaves (24.83%), matured leaves (23.10%), matured but lignified leaves (23.48%) and matured leaves (19.97%) at all harvesting period. The Physico-chemical characteristics of the oil on the main effect of HS has significantly (p<0.05) influenced refractive index (R.I) and has a highly significant (p<0.01) influence on the specific gravity (S.G) of the oils.