Content of Biologically Active Substances and Antioxidant Properties of Some Species of the Genus Agastache Clayton ex Gron. during the Growing Season

Objective: To analyze the content of biologically active substances (BAS) and antioxidant properties of four Agastache species (A. rugosa, A. foeniculum, A. urticifolia, A. mexicana) across different phenological phases. Methods: Content of flavonols, catechins, tannins, pectins, protopectins, saponins, and carotenoids in leaves, inflorescences, and stems was determined using spectrophotometric and gravimetric methods. Total antioxidant content (TAC) was measured by amperometry. Results and Discussion: Leaves and inflorescences were the main BAS accumulators. Tannin content in leaves was twice that in inflorescences, while carotenoids were an order of magnitude higher in leaves. Maximum TAC (>2 mg/g) was found in leaves during mass flowering. Catechins and tannins showed the strongest correlation with antioxidant activity (r = 0.69 and 0.63, respectively). Conclusions: The flowering period is the optimal time for harvesting Agastache raw materials, as plants are richest in BAS and exhibit the highest antioxidant activity. The leaves are the most valuable plant part.