Comparison of Soxhlet, accelerated solvent and supercritical fluid extraction techniques for volatile (GC-MS and GC/FID) and phenolic compounds (HPLC-ESI/MS/MS) from Lamiaceae species.

INTRODUCTION: Plants from the Lamiaceae family have been known traditionally for their beneficial health-promoting properties, attributed to their anti-inflammatory, anaesthetic and anti-microbial effects.
OBJECTIVE: The purposes of this study was to characterise the essential oils from four Lamiaceae plants by applying different extraction techniques.
METHODS: Accelerated solvent (ASE), Soxhlet and supercritical fluid (SFE) extraction methods were compared for their efficiency in obtaining the essential oils from plants. The volatile compounds were identified by GC-MS and the main chemotype was quantified by GC with flame ionisation detection (FID). Phenolic compounds were identified and quantified by HPLC and electrospray ionisation (ESI) with MS/MS.
RESULTS: The essential oils Mentha piperita (ct. menthol/menthone), Rosmarinus officinalis L. (ct. eucalyptol/camphor) and Origanum vulgare (ct. carvacrol/thymol), whereas Thymus vulgaris L. was found to be a pure chemotype (ct. thymol). All three extracts also contained six phenolic compounds. The highest extraction yields were achieved by the Soxhlet and ASE techniques, with M. piperita and R. officinalis L. producing the highest concentrations of rosmarinic and carnosic acids. Finally, it was observed that M. piperita and O. vulgare produced the highest total phenolic content, whereas R. officinalis L. and T. vulgaris L. produced the highest anti-oxidant activity.
CONCLUSION: The ASE and Soxhlet extraction techniques presented the highest yields of volatile and phenolic compounds, showing their suitability to characterise the chemical profile of aromatic plants.