Five years ago, in 1986, only a limited number of glycosidically bound volatiles were known and little could be reported on the distribution of those compounds in the plant kingdom. Since then an explosion of research activities in this field has led to the publication of many interesting results concerning structurally diverse terpenoid and non-terpenoid glycosides, their occurrence, and their role in different plant species. Up to now, about 200 different aglycone structures have been found in about 150 species belonging to 35 different families including ferns, gymnosperms, dicotyledons, and monocotyledons.All the diverse results concerning the role of these compounds in the plants should not lead us into ascribing to them an exclusive role, such as being involved in essential oil metabolism, as early workers have postulated. Although considering new electron microscopical observations of a transformation of carbohydrate-rich substances into lipophilic droplets at the tonoplast of Menha x piperitu secretory cells, the range of possible roles should not be underestimated. New experimental work should not only provide new analytical data but should also attempt to throw more light on the role of the glycosides.

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The inhibitory activity of manuka oil against Herpes simplex virus type 1 (HSV-1) and Herpes simplex virus type 2 (HSV-2) was tested in vitro on RC-37 cells (monkey kidney cells) using a plaque reduction assay. In order to determine the mode of antiviral action of the essential oil, manuka oil was added at different times to the cells or viruses during the infection cycle. Both HSV types were significantly inhibited when the viruses were pretreated with manuka oil 1 h prior to cell infection. At non-cytotoxic concentrations of the essential oil, plaque formation was significantly reduced by 99.5 % and 98.9 % for HSV-1 and HSV-2, respectively. The 50 % inhibitory concentration (IC (50)) of manuka oil for virus plaque formation was determined at 0.0001 % v/v ( = 0.96 microg/mL) and 0.00006 % v/v ( = 0.58 microg/mL) for HSV-1 and HSV-2, respectively. On the other hand, pretreatment of host cells with the essential oil before viral infection did not affect plaque formation. After virus penetration into the host cells only replication of HSV-1 particle was significantly inhibited to about 41 % by manuka oil. Flavesone and leptospermone, two characteristic ss-triketones of manuka oil, inhibited the virulence of HSV-1 in the same manner as the essential oil itself. When added at non-cytotoxic concentrations to the virus 1 h prior to cell infection, plaque formation was reduced by 99.1 % and 79.7 % for flavesone and leptospermone, respectively.

The in vitro antibacterial and antifungal activities of Australian tea tree oil, cajuput oil, niaouli oil, kanuka oil and manuka oil as well as of a beta-triketone complex isolated from manuka oil were investigated in a constituent-oriented study. The compositions of the oils were analysed by capillary GLC and GLC-MS. The MICs for sixteen different microorganisms were determined applying the broth dilution method. Australian tea tree oil showed the best overall antimicrobial effect. The best inhibitory effects on Gram-positive bacteria and dermatophytes were achieved with manuka oil due to its beta-triketone content.

People have used thyme (Thymus vulgaris L. -Labiatae) for many centuries as a fl avouring agent, culinary herb and herbal medicine. It is indigenous in the Mediterranean region, especially on the Iberian Peninsula and in Northwest Africa and is grown commercially in a number of countries for the production of the dried leaves, thyme oil, thyme extracts, and oleoresins. This chapter presents the history, botany and morphology of thyme, together with its chemical structure, production and harvesting. The main uses of thyme in food processing and its functional properties and toxicity are described along with its pharmacopoeial status and applicable quality specifi cations.