Changes in qualitative characteristics of garden thyme (Thymus vulgaris L.) as affected by cold plasma

Abstract

Cold plasma (CP) is one of the emerging technologies capable of creating special capabilities in agricultural products by affecting their surfaces. This technique can increase the content of essential oil extracted from active ingredients, while reducing the microbial load of medicinal and aromatic crops. In order to investigate the effect of dielectric barrier discharge cold plasma (DBD-CP) on the qualitative characteristics of thyme (Thymus vulgaris L.), dried leaves were used for treatments. The experiment was performed with two variables of time (30, 60, 120 & 300 s) and voltage (17, 19, 21 & 23 kV). The results showed that the hydrophilicity of the samples was improved by CP treatment, while few changes were observed in leaf color characteristics. Scanning electron microscopy showed that increasing the treatment duration and the voltage could cause rupture and wrinkles in the glandular trichomes. Although the DBD-CP treatments increased the essential oil extraction efficiency of the leaves (by approximately 20 %), they did not significantly affect the essential oil components nor the amount of two important compounds, thymol and linalool, which increased slightly (3.7 % and 3.5 %, respectively). It can be concluded that DBD-CP can be used as a pretreatment and auxiliary tool in improving the extraction efficiency of thyme and does not have a negative effect on its essential oil components.