The Effect of Pretreatment Type on the Yield of Essential Oils from Eucalyptus Species (Camaldulensis And Torelliana ) Using Steam Distillation

In recent years, low yields and suboptimal physicochemical and phytochemical qualities of essential oils from medicinal plants have driven research into improved extraction and pretreatment methods. This study investigates how three pretreatment types—wet (fresh), chilled (–4 °C), and air-dried—affect the yield and chemical composition of essential oils obtained from Eucalyptus camaldulensis and Eucalyptus torelliana leaves using indirect steam distillation. Leaves were cut to increase surface area, subjected to the different pretreatments, and distilled at 100 °C over varying times (30–182 min for E. camaldulensis and 30–240 min for E. torelliana). The highest yields were obtained from chilled leaves, with 1.4% at 135 min for E. camaldulensis and 1.73% at 224.25 min for E. torelliana, the latter showing a higher yield at longer extraction time. The enhanced performance of chilled pretreatment is attributed to cell structure disruption by freezing, which facilitates oil release. GC–MS analysis was used to characterize the chemical composition of the extracted oils, confirming that pretreatment methods significantly influence both yield and composition of Eucalyptus essential oils from these two species. This has implications for optimizing local industrial production and improving the economic viability of Eucalyptus oil extraction in Nigeria.