Ozone as eustress for enhancing secondary metabolites and bioactive properties in Salvia officinalis

Eliciting plants consists in the application of chemical, physical, and biological factors that induce stressful conditions, and so trigger defense mechanisms and the production of bioactive compounds and phytochemicals. In this study, the phenolic and volatile organic compound (VOCs) profiles of sage leaves under a chronic ozone (O3) exposure (120 ppb 5 h day− 1 for 36 consecutive days) were investigated, elucidating also their antioxidant activity. The composition, yield, and antioxidant capacity of essential oils (EOs) obtained from sage leaves were also evaluated. Ozone exposure resulted in an overall increase of phenolic compounds. In terms of VOCs, O3 mainly reduced monoterpene emissions, while increased the production of sesquiterpenes (in both leaves and EOs). These O3-induced accumulations were triggered during the first weeks of exposure, whereas they dis- appeared at the last time of analysis, suggesting that sage plants lost their ability (or interest) in activating secondary metabolism under high doses of O3. The antioxidant capacity of all tested extracts resulted increased by O3 exposure. These outcomes support our speculation that the application of O3 for a limited period (i.e., a maximum of four weeks, at the investigated concentration) may become an effective biotechnological tool to improve the quality of sage leaf extracts.