Characterization of the antioxidant properties of aroma constituents isolated from medicinal plants

Aroma extracts isolated from medicinal plants have been widely used in aromatherapy and their aroma components are believed to possess medicinal properties, as well as antioxidant activity. Aroma extracts isolated from medicinal plants such as clove buds, eucalyptus leaves, and various beans, were prepared and examined for antioxidant activity by three different assays. The antioxidative activity of aroma extracts of mung beans, soybeans, and cloves as well as major aroma chemicals like eugenol, eugenyl acetate, and thymol were comparable to that of the natural antioxidant, alpha-tocopherol (vitamin E). The aroma extracts isolated from soybeans, mung beans, kidney beans, and azuki beans inhibited the oxidation of hexanal for nearly one month at a level of 250 muL/mL. Mung bean and soybean extracts inhibited malonaldehyde (MA) formation from cod liver oil by 86% and 88%, respectively, at 250 muL/mL level. Aroma compounds contained in the extracts of soybean and mung bean were identified by gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS). Among identified chemicals, eugenol, maltol, benzyl alcohol and 1-octen-3-ol inhibited the oxidation of hexanal by 100%, 93%, 84%, and 32%, respectively, for a period of 40 days at concentrations of 500 mug/mL. Eugenol, maltol, benzyl alcohol, and 1-octen-3-ol inhibited MA formation from cod liver oil by 91%, 78%, 78%, and 78%, respectively, at the 160 mug/mL level.;The aroma extract isolated from clove buds [Syzygium aromaticum (L.) Merr. et Perry] inhibited the oxidation of hexanal for 30 days at a level of 50 mug/mL. Clove bud extract inhibited MA formation from cod liver oil by 93% at concentration of 160 mug/mL. The major aroma constituents of clove buds, eugenol and eugenyl acetate inhibited the oxidation of hexanal by 99%, and 99%, respectively, for a period of 30 days at 500 mug/mL. Eugenol and eugenyl acetate inhibited MA formation from cod liver oil by 88% and 79%, respectively, at concentration of 160 mug/mL. The aroma extract isolated from eucalyptus leaves [Eucalyptus polyanthemos Schauer] inhibited the oxidation of hexanal completely for 30 days at a level of 200 mug/mL. and 500 mug/mL. The eucalyptus aroma extract inhibited MA formation from cod liver oil by 86% at the 160 mug/mL level. Thymol, one of the major aroma chemicals in the extract, inhibited the hexanal oxidation by 100% at 500 mug/mL level for 30 days. In lipid/MA assay, thymol inhibited MA formation by 80% at the level of 160 mug/mL.;The inhibitory effect of aroma extracts isolated from soybeans, mung beans, clove buds, and eucalyptus leaves on MA formation from horse blood plasma oxidized with Fenton's reagent was also assessed. Among the extracts tested, soybeans and clove exhibited the potent antioxidant activities comparable to that of alpha-tocopherol. The extract of soybeans, clove, and alpha-tocopherol inhibited MA formation by 58%, 48%, and 52%, respectively, at the level of 400 mug/mL.