Age and harvest season affect the phenylpropenoid content in cultivated European Rhodiola rosea L

Characteristic phenylpropenoids are a quality marker to distinguish rhizome and root of authentic Rhodiola rosea L. from other Rhodiola species. A consistent content in line with pharmacopoeial requirements is one objective of increasing cultivation to satisfy the worldwide demand. We set out to compare the influence of harvest season and age on total rosavins (ROStot) and their aglycon cinnamyl alcohol (CA) determined by HPLC/DAD. Plants from 9 different European origins were grown homogenously in South England and harvested in March, August and November of cultivation years 3–5. For experiment optimisation and validation we initially studied other factors that influence the chemical profile: sample origin (plants, herbal drugs and final products of different origin), plant part (rhizome, root, herb), drying (temperature and duration), extraction (solvent strength). We also investigated differences between plant individuals of the same provenance such as male and female plants.Pre-tests showed the importance of confirmed plant identity as non-authentic samples are indicated by total and relative amounts of phenylpropenoids vis-a-vis phenylethanoids. Rhizomes contained 2–3 times higher ROStot values than roots. There was no substantial influence of drying temperature (45°C versus 65°C), but drying at room temperature longer than 10 days influenced negatively phenylpropenoid values. ROStot are best extracted with 70–90% ethanol; CA with 50–70% ethanol. No significant influence of plant sex on the phenylpropenoid content was detected.Extracts (70% ethanol) from R. rosea rhizomes contained 0.5–4.1mg/mL total rosavins corresponding to 0.31–2.6% in the dry drug. Across all provenances the ROStot and to less extent the CA content in rhizomes was significantly higher when harvested in March than in August or November alongside a decrease from year 3 to year 5 under our cultivation conditions. The CA content was 5–30% of ROStot with some influence of the plant origin and may be considered for drug identification and standardisation.