Effect of harvest year on production, chemical composition and antioxidant activities of essential oil of oregano (Origanum vulgare subsp glandulosum (Desf.) Ietswaart) growing in North Africa

• Chemical composition of Origanum vulgare subsp glandulosum (Desf.) Ietswaart essential oils in related to harvest years.
• Qualitative, quantitative changes and antioxidant activities in the oregano essential oil produced in the North Africa region during the years 2007, 2008 and 2009.
• The Tunisian oregano essential oil was more affected by rainfall than the temperature.

Dried flowers and leaves of Origanum glandulosum (Desf.) Ietswaart collected at different harvesting years were submitted to hydrodistillation. The isolated essential oils were analyzed by GC and GC/MS to study the harvest year effect on oregano chemical composition. Total phenolic contents and antioxidant effectiveness were performed. Nefza essential oils were obtained in yields of 4.6%, 5.8% and 4.3% from plants collected in 2007, 2008 and 2009, respectively. The values of essential oil content of Krib population were close (2-2.7%). There are qualitative and quantitative differences in the chemical composition of essential oils of Krib and Nefza populations from one harvest year to another. p-cymene, γ-terpinene, thymol and carvacrol are the main compounds of all oils, regardless of the year of harvest. The year that has the highest value in rainfall and which declines in cooler conditions during the flowering period, has been the most important value in essential oil yield. Wide variations were noted in total phenolic content, expressed in gallic acid equivalent which varied in Nefza population, between 8.52–17.67 g GAE/kg dw. The anti-radical activity expressed by IC50 of oregano essential oils was varied from one year to another, from 59.2 mg/L in 2007, to 226.19 mg/L in 2008 for Nefza population. Those of Krib varied from 79.8 to 151.85 mg/L. The controlled culture of oregano is better that using the wild populations if we would like have stable constituents destined to the industries or pharmacological uses. So, we can adjust the controlled parameters of our culture according to our purpose.