Effects of steam and vacuum administration during decontamination on essential oil content in herbal medicines

Saturated steam decontamination is an application for elimination of microorganisms from the surface of different materials. This technique has been optimized for the treatment of dried spices or pharmaceuticals, which could have been contaminated with microorganisms during cultivation, processing, storage or transport. The described saturated steam decontamination is based on the Lemgo process. This method does not kill microorganisms, but removes them physically from the surface. Our investigation focused on measuring the effects of steam temperatures at 120 °C and 100 °C, respectively, for 20 s with a subsequent fl ash vacuum of 20 s. Applications of fl ash vacuum as well as saturated steam heated to 120 °C were also tested separately. The impact of these parameters on the essential oil content and on the surface of different medicinal plants such as marjoram, oregano, fennel and eucalyptus was analysed using gas chromatography and scanning electron microscopy. Especially in herbal drugs with glandular trichomes such as marjoram and oregano severe surface destruction was visible accompanied by high losses of essential oil from 93 % in marjoram tissue to 59 % in oregano tissue. For fennel and eucalyptus that possess protected essential oil storage cells only minor or no reduction of volatiles has been observed during exposure to saturated steam. The experiments show clearly a positive correlation between stability of essential oil cavities and essential oil content preservation.