The aim of the study was to determine the effect of plant age and growth phase on the accumulation of phenolics in stem bark, leaves and underground organs of Eleuthero. Their content was assessed using validated HPLC-DAD method. In underground organs and stem bark 7 phenolics were determined, i.e. eleutherosides B and E as well as caffeic, ferulic, chlorogenic, rosmarinic and protocatechuic acids. The content of eleutherosides B was significantly higher in stem bark while eleutherosides E, in underground organs. Accumulation of these compounds was the highest in the 4-year-old plants (87.43 mg·100 g^–1 DW of eleutherosides B and 85.22 mg·100 g^–1 DW of eleutherosides E in underground organs; 302.21 mg·100 g^–1 DW of eleutherosides B and 24.89 mg·100 g^–1 DW eleutherosides E in stem bark). In these organs, among identified phenolic acids chlorogenic acid was the dominant. In the leaves 4 phenolic acids (caffeic, ferulic, chlorogenic and rosmarinic acids), as well as 2 flavonoids (rutoside and hyperoside), were identified. Flavonoids and caffeic acid occurred in higher amounts at the beginning of leaf senescence, whereas the other phenolic acids – at the full vegetation. Their content was the highest in 2-year-old plants.

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