Selective extraction of oxygenates from savory and peppermint using subcritical water

Abstract

The yields of oxygenated and non-oxygenated flavour and fragrance compounds from savory (Satureja hortensis) and peppermint (Mentha piperita) were compared using subcritical water extraction, supercritical carbon dioxide extraction (SFE) and hydrodistillation. Extraction rates with subcritical water increased with temperature (100–175 °C), but some desired organics (linalool and γ-terpinene) showed substantial degradation at temperatures >150 °C. However, subcritical water did not expose extracted compounds to atmospheric oxygen (as occurs in hydrodistillation) and thus may avoid the degradation of compounds like thymoquinone. Extraction of savory with subcritical water at 100 °C for 40 min gave ca. 100% recoveries (compared to hydrodistillation) for thymol and carvacrol, and >150% recoveries of borneol and linalool. Recoveries with 60 min of SFE (pure CO2 at 400 bar and 50 °C) were similar to hydrodistillation for borneol and linalool, but only ca. 50% for thymol and carvacrol. For peppermint, 30 min (at 150 °C) or 12 min (at 175 °C) of subcritical water extraction and 1 h of SFE gave good quantitative agreement with 4 h of hydrodistillation for carvone, pulegone, piperitone, eucalyptol, menthone, neomenthol and menthol, but the short subcritical water extractions only recovered ca. 40% of the less polar menthyl acetate. Subcritical water preferentially extracts more polar (oxygenated) flavour compounds, and ca. 80% extraction of oxygenated flavour compounds could be achieved under conditions which only extracted ca. 10–15% of the monoterpenes and <5% of the sesquiterpenes. In contrast, SFE had the lowest degree of selectivity and SFE extracts included plant alkane waxes as well as the same flavour compounds recovered by hydrodistillation. Copyright © 2001 John Wiley & Sons, Ltd.