EFFECT OF MOISTURE STATUS ON SPEARMINT (Mentha spicata var. viridis L.) OIL CONTENT AND PHYSICO-CHEMICAL PROPERTIES

The experiment was conducted to evaluate the effect of moisture status on spearmint oil content and physico-chemical properties. Three moisture levels were investigated: Freshly harvested plants, semi-dried (over-night dried) and fully dried under shade for 5 days respectivament, with 74.3%, 48.2%, and 3.6% of moisture. Essential oil extraction and analyses of physicochemical properties were made according to the British Pharmacopoeia methodology and British Standards Institute, respectively. Oil content calculated on dry weight basis was significantly higher in the fresh harvested herb (2.72 ml/100 g dry wt.), followed by the semi-dried (2.61 ml/100 g dry wt.) and least in the dry (2.59 ml/100 g dry wt.). Relative density was highest significantly in fresh herb oil (0.921), followed by semi-dry (0.916) and lastly the dry (0.907). Refractive index followed the same pattern of relative density (1.4795), (1.4788) and (1.4773). Optical rotation significantly decreased from fresh herb oil (-46.650), semi-dried (-46.625) and lowest in the dry (-46.615). Acid value highest in fresh herb oil (0.84165), followed by semi-dry (0.67332) and least in the dry (0.63124). Ester value was significantly lowest in fresh herb oil (14.025), followed by semi-dry (19.635) and the highest in the dry (21.0375).