Changes in the concentrations of bioactive compounds in plantain leaves.

The plantain is used in herbal medicines and for pasturage. Two cultivars of plantain (Plantago lanceolata L.), Grasslands Lancelot and Ceres Tonic, were sown in spring. Changes in catalpol, aucubin, and acteoside concentrations in the leaves during the growing season and by drying after harvesting were quantitatively determined by high-performance liquid chromatography. The concentration of catalpol was relatively low, fluctuating between 1 and 2% of dry matter during the growing season, and there was no clear-cut seasonal change. From spring to midfall, the aucubin concentration increased from 2.1 to 4.8% in Grasslands Lancelot and from 1.0 to 2.7% in Ceres Tonic. These increases were gradual over the season, except for during midsummer, when aucubin concentrations were relatively constant. The acteoside concentration increased from 3.4 to 7.1% in Grasslands Lancelot and from 1.5 to 4.1% in Ceres Tonic over the course of the growing season, although in the summer it declined steadily to lows of 2.5% in Grasslands Lancelot and 1.9% in Ceres Tonic. Our data suggested that midfall was the appropriate time for harvesting plantain for medicinal use. The concentrations of the bioactive compounds steadily decreased in the initial stages of drying both under natural climatic conditions and at 60 degrees C. The development of processing methods to minimize the loss of bioactive compounds is imperative.