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Abstract
The effect of moisture and plant growth on Mexican oregano (Lippia graveolens HBK) essential oil composition was examined in field trials. Essential oil content of dry oregano leaves was about 2% (w/w). Thymol and carvacrol were the major components in the oil fraction and plant maturity had a significant effect on oil composition. However, moisture effect and plant growth phase/moisture interaction were not significant. Examination of the oil composition of samples collected from three cultivated and one wild oregano type indicated that the oil obtained from wild plants contained significantly lower amount of 1,8-cineole and carvacrol than the cultivated types. The thymol content of the wild variety was higher.
Key Word Index
Lippia graveolens, Verbenaceae, Mexican oregano, essential oil composition, p-cymene, 1,8-cineole, γ-terpinene, thymol, carvacrol, moisture effect, plant growth phase effect.
Introduction
A number of plants in various plant families are commonly referred to as oregano and/or origanum. This genus covers a wide range of species and subspecies. A list of these plants is reported by Lawrence (1). Greek [Origanum vulgare L. ssp, hirtum (Link) letswaart], Turkish (Origanumonites L.), Spanish (Thymus capitatus (L.) Hoffmanns et Link) and Mexican oregano (Lippia graveolens HBK) are the species of economic importance.
Origanum species have been used for centuries as spices and in traditional medicine. Today, oregano is one of the major culinary herbs in world trade. Oregano essential oils are commonly used to prepare flavors and as ingredients in toothpaste, chewing gum and in the preparation of fragrances. Oregano is considered as GRAS (Generally Recognized as Safe) by the United States Food and Drug Administration. Foods flavored with oregano oil include alcoholic beverages, baked goods, meats and meat products, condiments and relishes, milk products, processed vegetables, snack foods, and fats and oils.
Aroma in spices is a complex mixture of volatile compounds such as terpenes, sesquiterpenes and oxygenated derivatives. There have been a number of reports that essential oils of aromatic plants possess antioxidant activities (2-4). This property was attributed to the presence of hydroxyl groups in their phenolic components. Antimicrobial, cytotoxic and antifungal activities of oregano oil have been also reported (5,6). The chemical composition of Greek, Turkish and Spanish oregano has been studied by several research groups (7-9). Depending on the species, thymol...