Supercritical CO2 extraction of volatile thymoquinone from Monarda didyma and M. fistulosa herbs

•Monarda plants contained 0.7–2.1 mg/g biologically active thymoquinone.•Thymoquinone recovery with supercritical CO2 was 81–88% at 12 MPa and 40 °C.•Thymoquinone content in extract was increased applying short extraction times.•We discuss the loss of most volatile monoterpenes in the stream of gaseous CO2.•We confirm inefficiency of thymoquinone separation from plants by hydrodistillation.

Volatile oil rich in thymoquinone (TQ) was extracted from dry aerial parts of scarlet bee balm (Monarda didyma) and wild bergamot (Monarda fistulosa) with supercritical CO2. The optimum extraction conditions were determined as 12 MPa and 40 °C for both yield (0.6 mg TQ/g M. didyma and 1.7 mg TQ/g M. fistulosa) and high TQ concentration in extract (5.2 and 10.2% w/w, resp.). The difference in the extraction kinetics of volatile oil and cuticular waxes was examined. The supercritical fluid extraction was compared with hydrodistillation and Soxhlet extraction with hexane. Substantial thymoquinone loss during hydrodistillation was confirmed. The extraction with hexane ensured maximum TQ yields (0.7 and 2.1 mg/g, resp.) but TQ concentration in the extracts was lower (2.6 and 3.8%).

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