Polyphenolic composition of roots and petioles of Rheum rhaponticum L.
BACKGROUND
Various species of the genus Rheum (Polygonaceae) are known for their high content of medicinally important hydroxyanthraquinones. However, little information is available concerning the polyphenolic composition of garden or dietary rhubarb Rheum rhaponticum L. (R. rhaponticum).


OBJECTIVE
Determination of further polyphenols in the roots and petioles of R. rhaponticum.


METHODS
The dried plant material was extracted with 10-fold excess (v/w) of methanol and subsequently diluted five times with methanol-water (1:1) and analysed by reversed-phase liquid chromatography using tandem UV-photodiode array and mass selective detection (RP-HPLC-UV-ESI/MS(2)). Polyphenols were identified using either HPLC-ESI/MS(2) data obtained for respective commercial standards or by comparison of a parent ion fragmentation picture with the respective MS(2 )spectrum from the literature.


RESULTS
The roots of R. rhaponticum were very rich in various hydroxystilbenes and contained four main substance groups--derivatives of trans-piceatannol, trans-resveratrol, trans-rhapontigenin and trans-deoxyrhapontigenin. Additionally, pterostilbene acetylglucosides and a number of hydroxyanthraquinones and their glycosides were identified in the root samples. The profile of polyphenols in the petioles of R. rhaponticum was similar to that of the roots but the content of individual substances was remarkably lower. The petioles of the R. rhaponticum additionally contained significant amounts of derivatives of flavonol quercetin, which is a good antioxidant.


CONCLUSIONS
The study has shown that roots of R. rhaponticum contain a wide variety of hydroxystilbenes and deserve further consideration as a source of medicinally interesting compounds.
Püssa
Tonu
T
Department of Food Science and Hygiene, Estonian University of Life Sciences, Kreutzwaldi 58A, 51014 Tartu, Estonia.
Raudsepp
Piret
P
Kuzina
Kristina
K
Raal
Ain
A
D002851:Chromatography, High Pressure Liquid / Q000379:methods; D005419:Flavonoids / Q000032:analysis*; D035264:Flowers / Q000737:chemistry*; D010636:Phenols / Q000032:analysis*; D018517:Plant Roots / Q000737:chemistry*; D059808:Polyphenols; D012250:Rheum / Q000737:chemistry*; D012680:Sensitivity and Specificity; D021241:Spectrometry, Mass, Electrospray Ionization; D013056:Spectrophotometry, Ultraviolet / Q000379:methods
D005419:Flavonoids; D010636:Phenols; D059808:Polyphenols