Effect of different drying techniques on the aroma profile of Thymus vulgaris analyzed by GC–MS and sensory profile methods

In the case of Thymus vulgaris L. the effect of different drying techniques (natural way, convective drying at 30 °C, 40 °C and 50 °C and lyophilization) were investigated on the quantity and quality parameters of the final product analyzed by GC–MS and sensory profile methods. Measured essential oil amounts were between 0.69 ml/100 g and 1.84 ml/100 g calculated on the dry weight basis. The highest drying temperature (50 °C) and lyophilization caused the most considerable essential oil loss; the different primary processing methods also influenced significantly the essential oil composition. Referring to the main essential oil compound – thymol – the ratios varied between 58.57% (detected in the samples dried at 30 °C) and 71.19% (found in the lyophilized material). Based on the data of the sensory analysis, the preference of the spice was mainly determined by the freshness, ratio of the purple colour, ratio of 1,8-cineol and thymol; even if the essential oil amount of the spice did not meet the requirements of the Pharmacopoeia. According to our results, sensory analysis data in most of the cases corresponds to the GC–MS measurements and gives a much more complex characterization of a garden thyme spice.

► Drying at 50 °C and lyophilization cause considerable loss of the essential oil.
► Because of the too long drying process, the ratio of thymol decreases.
► Preference is determined by freshness, ratios of 1,8-cineol and thymol.
► Lyophilized and 40 °C dried samples are the most preferred ones by the consumers.