Content and Composition of Volatile Terpenes, Flavonoids and Phenolic Acids in Greek Oregano (Origanum vulgare L. ssp hirtum) at different Development Stages during Cultivation in Cool Temperate Climate

Plants of Origanum vulgare ssp. hirtum (Greek oregano) were cultivated in two years in a cool temperate climate and the aerial parts were harvested at up to five different development stages during the growing season (July to late August) in order to investigate how the content of volatile terpenes and polyphenols depends on the development stage of the plants. Volatile terpenes were identified and quantified in dichloromethane extracts by GC-MS and GC-FID, respectively. Polyphenols were quantified in aqueous methanol extracts by RP-HPLC-PDA and identified by LC-PDA-MS and NMR spectroscopy. Significant changes in the concentrations and composition of major volatile terpenes (carvacrol, gamma-terpinene, p-cymene, myrcene, alpha-pinene, beta-caryophyllene, thymol) were observed at the different development stages. The content of volatile terpenes varied from 3.7-4.9% (year 1) and 2.6-4.6% (year 2). The potential yields of total volatile terpenes varied from 74-165 kg ha(-1) (year 1) and 31-79 kg ha(-1) (year 2) being highest near full flowering stage (50-60% open flowers). Major polyphenols were eriodictyol 6,8-di-G-glucoside, apigenin 6,8-di-G-glucoside, luteolin 7-O-glucuronide, epi-lithospermic acid B, lithospermic acid B and rosmarinic acid. The content of flavonoids varied from 4.8-7.7 mg g(-1) dry matter (DM) (year 1) and 8.9-12.4 mg g(-1) DM (year 2), and phenolic acids from 1.4-10.1 mg g(-1) DM (year 1) and 23.4-51.5 mg g(-1) DM (year 2). The highest content of flavonoids in aerial parts was obtained near full flowering stage and for phenolic acids earlier at around 10-20% open flowers. The conclusion of this study is that also in a cool temperate climate the development stage has a significant impact on the content and composition of both volatile terpenes and polyphenols in O. vulgare ssp. hirtum, and that an optimal harvest time of aerial parts of this plant depends on the secondary metabolites of interest.