Influence of drying techniques on the volatile phenolic compounds, chlorophyll and colour of oregano (Origanum vulgare L. ssp. prismaticum Gaudin).

Abstract

Raw and blanched oregano (Origanum vulgare L. ssp. prismaticum Gaudin) were air-dried at 35° and 50°C in two drier pilot plants; raw oregano was also dried at room temperature in a shady place. Oregano leaves were analysed for volatile phenolic compounds by GC/MS-SIM, for chlorophyll by HPLC and for colour by reflected-light colorimetry. The highest contents of thymol and carvacrol were found in unblanched oregano dried at 35°C, followed by oregano dried at room temperature and by both samples dried at 35° and 50°C after blanching. The highest chlorophyll content was identified in oregano dried at room temperature, followed by unblanched oregano dried at 50°C and blanched oregano dried at 35°C. All unblanched, air-dried oregano leaves had colour attributes similar to the raw ones, while blanched-dried leaves were greener. The least damaging treatments were air-drying at 35° and 50°C without blanching.