Abstract

The effects of hydrodistillation (HD) and solvent free microwave extraction (SFME) methods on the chemical composition and toxicity of Mentha longifolia subsp. capensis leaves were studied. Colourless oils of 1.52 and 1.63% (wet/dry weight) were obtained from HD and SFME methods, respectively. Analyses of the two oils revealed a total of 21 components. These accounted for about 80% of the total oil composition. The HD oil was found to be characterized by monoterpenoids with oxygenated monoterpenes, such as menthone (41.9%), a-pinene (5.4%), pulegone (34.2%), β-pinene (2.4%) and 1, 8-cineole (6.5%). Other identified constituents, include cis-sabinene hydrate (0.4%), linalool (1.0%), piperitenone (1.3%), β-caryophyllene (0.4%), germacrene D (0.5%) and isomenthone (0.4%). However, the hydrodistilled oil showed the presence of 3 octanol (0.2%), bicyclogermacrene (0.1%) and caryophyllene oxide (0.1%) which were not found in the oil extracted with solvent free microwave extractor. The SFME oil was characterized by menthone (28.0%), a-pinene (3.6%), pulegone (23.0%), β-pinene (1.0%) and 1, 8-cineole (5.4%). Other identified constituents, include cis-sabinene hydrate (0.1%), linalool (0.5%), piperitenone (0.1%), β-caryophyllene (0.3%), germacrene D (0.2%) and isomenthone (0.3%). In vitro cytotoxicity test was also studied by brine shrimp lethality bioassay. At 40 µg/ml which was the least concentration used, the oil was not toxic; all the brine shrimps survived. While maximum mortalities happened at 200 µg/ml, the least mortalities were observed at 40 µg/ml.

Key words: Mentha longifolia, essential oils, hydrodistillation, solvent free microwave extraction, toxicity.