Seasonal variation of lipophilic compounds of Urtica dioica L. leaves

Abstract

Objective: phytochemical characterization of Urtica dioica L. leaves and the selection of the raw materials with the highest content of sterols and carotenoids, in order to obtain pharmacologically active extracts. Material and methods. The leaves were harvested for a period of 7 months (March – September) from Racari Village, Dambovita County, Romania, in 2010. The batches were codified as B1 (March), B2 (April), B3 (May), B4 (June), B5 (July), B6 (August), B7 (September). In order to confirm the identity of the leaves, macroscopic, microscopic and qualitative exams were undertaken. The sterols (free and glycosidic sterols) were assessed spectrophotometrically, based on the formation of dehydration products with multiple conjugated double bonds in the presence of concentrated sulfuric acid and ferric chloride (catalyst). The carotenoids content were determined, before and after their release from esteric forms, by assessing the absorbance at λ = 460 nm. Results. The morphological and anatomical aspects concur with scientific literature. The leaves are thin and complete, with a triangular and pubescent lamina (L=0.5 to 10 cm, l=0.3 to 5 cm).The margin is serate and the apex is acuminate. The upper surface is dark green and the lower surface is light green. In all batches, the microscopic exam shows the following specific anatomical elements: subulate hairs and stinging hairs, secretory trichomes with bicellular heads and unicellular stalks, cluster-crystals of calcium oxalate. The active principles identified in the qualitative examination are: sterols, carotenoids, coumarines, flavonoids (except batch B4), polyphenolcarboxilic acids, tannins, proanthocyanidins, mucilages. The carotenoids determination indicates that the highest content of free and esteric forms are found in leaves harvested in June and July, respectively. Glycosidic sterols are prevailing. The leaves content of glycosidic sterols is increases with maturity of the plant. The highest content of free sterols was determined in samples harvested in May. Conclusions. The leaves of Urtica dioca L. represent a complex source of active principles. The selected batch was B3. The selection of the batch was based on the total amount of carotenoids and sterols.