Biomass, Phenolic Compounds, Essential Oil Content, and Antioxidant Properties of Hyssop (Hyssopus officinalis L.) Grown in Hydroponics as Affected by Treatment Type and Selenium Concentration

Abstract

Hyssop (Hyssopus officinalis L.) is an aromatic plant that is rich in various biologically active compounds and is widely used as a natural preservative and flavoring agent in the food and cosmetic industry and as a folk medicine against certain respiratory diseases. Despite the fact that selenium is not an essential trace element for plants, in a certain range of concentrations it can not only improve plant growth, but also increase the content of nutrients and biologically active compounds in plants. In the present study, the effect of treatment type (in a nutrient solution (NS) or by foliar application (FA)) and selenium (Se) concentration (2.0, 5.0, 10.0, 20.0, 40.0 μM) on the biomass, phenolic compounds, essential oil content, and antioxidant properties of hyssop grown in hydroponics was studied. Neither a toxic nor a beneficial effect of Se addition on the plants was observed. Selenium treatment significantly increased Se concentration in hyssop up to 38.35 μg g−1 (NS) and 34.86 μg g−1 (FA). The effect of selenium on the content of phenolic compounds, essential oil, and the antioxidant activity of hyssop depended on the applied selenium concentration. Hyssop treated with 10 μM Se (NS) and with 20 μM Se (FA) had a higher total content of hydroxycinnamic acids and higher contents of rosmarinic and chlorogenic acids, as well as a higher total content of phenolic compounds, higher content of essential oil, and higher antioxidant activity compared to other experimental plants. The results confirm the feasibility of selenium treatment of hyssop without reducing its production in order to enhance its nutritional and pharmaceutical properties.