Effect of drying on the volatile constituents of thyme (Thymus vulgaris L.) and sage (Salvia officinalis L.)

The losses of volatile constituents in herbs and spices depend mainly on drying parameters and biological characteristics of the plants. In the present study, two methods were applied in the analysis of the effect of drying on the aroma constituents of the widely used herbs thyme (Thymus vulgaris L.) and sage (Salvia officinalis L.). The volatile constituents of herbs (fresh, freeze-dried and ovendried at 30 °C and 60 °C) were isolated by dynamic headspace and simultaneous distillation-extraction methods and analysed by capillary gas chromatography and coupled gas chromatography-mass spectrometry. In total, 68 compounds were identified in thyme and 44 in sage, and more than 100 components were screened quantitatively. A significant reduction in the amount of extracted volatiles was found only in the case of drying at 60 °C, mainly as a result of the loss of non-oxygenated monoterpenes. The character of the changes of the headspace volatiles was more complex, especially for thyme, the content of aroma compounds being the highest when the herb was dried at 60 °C. Some aroma assessment criteria (coefficient of efficiency Ce) are proposed on the basis of the results obtained.