Comparison between supercritical CO2 extraction and hydrodistillation for two species of eucalyptus: yield, chemical composition, and antioxidant activity.

In this work, 2 Eucalyptus species extracts (Eucalyptus cinerea and Eucalyptus camaldulensis) were prepared by hydrodistillation (HD) and supercritical carbon dioxide extraction (SCE) techniques. The best yields of E. cinerea and E. camaldulensis (27.5 and 8.8 g/kg, respectively) were obtained using SCE at 90 bar, 40 °C compared to HD (23 and 6.2 g/kg, respectively). Extracts were quantified by gas chromatography-flame ionization detection and identified by gas chromatography-mass spectrometry. 1,8-cineole and p-menth-1-en-8-ol were the major compounds of E. cinerea essential oil obtained by HD (64.89% and 8.15%, respectively) or by SCE (16.1% and 31.87%, respectively). Whereas, in case of E. camaldulensis, 1,8-cineole (45.71%) and p-cymene (17.14%) were the major compounds obtained by HD, and 8,14-cedranoxide (43.79%) and elemol (6.3%) by SCE. Their antioxidant activity was assessed using 2 methods: 2,2-azino-di-3-ethylbenzothialozine-sulphonic acid radical cation (ABTS(•+) ) and 2,2-diphenyl-1-picrylhydrazyl radical (DPPH(•) ). In the SCE extracts from both E. cinerea and E. camaldulensis, a promising radical scavenging activity was observed with ABTS(•+) , (65 and 128 mg/L, respectively). The total phenolics composition of the extracts was measured and the range was 2 to 60 mg of gallic acid equivalent/g dry plant material. The SCE method was superior to HD, regarding shorter extraction times (30 min for SCE compared with 4 h for HD), a low environmental impact, allows production of nondegraded compounds and being part of green chemistry.