The Electrical Conductivity and Drying Method Changed the Secondary Metabolite Content and Photoprotective Effects of Hydroponically Cultivated Agastache rugosa Kuntze

Many studies have examined how various cultivation methods and elicitors elevate target crop values. Post-harvest treatments, such as the drying method, may alter the final product’s characteristics. We investigated the effect of nutrient solution concentration during the hydroponic cultivation and drying method (cold air drying and freeze drying) after harvesting Agastache rugosa Kuntze, an herb used for folk medicine and as a deodorant, spice, and tea in East Asia. To explore the properties of A. rugosa, we determined its growth parameters, secondary metabolites, and photoprotective effects. We observed the highest growth and yields in A. rugosa grown under 4.0 dS·m−1 electrical conductivity (EC) conditions. However, the EC 2.0 group showed higher antioxidative properties than those grown in EC 1.5 and 4.0 conditions. Drying conditions varied the content and ratios of major active compounds (rosmarinic acid, tilianin, and acacetin) in A. rugosa. Cold air drying caused rosmarinic acid transmutation to tilianin and acacetin, and tilianin showed a stronger positive correlation with antioxidative and photoprotective activities than rosmarinic acid. The increased tilianin content in cold-air-dried A. rugosa accompanied the improved photoprotective effects in dermal cell lines. This study reveals the effects of cultivation and drying methods in A. rugosa production, and proposes alternate industrial production techniques.