Research Article Received: 3 October 2007, Revised: 26 August 2008, Accepted: 2 September 2008 Published online 31 October 2008 in Wiley Interscience (www.interscience.wiley.com) DOI 10.1002/pca.1102 Copyright © 2008 John Wiley & Sons, Ltd. Phytochem. Anal. 2009; 20: 98–103 98 John Wiley & Sons, Ltd. Polyphenolic composition of roots and petioles of Rheum rhaponticum L. Tõnu Püssa, a Piret Raudsepp, a Kristina Kuzina b and Ain Raal b * ABSTRACT: Introduction – 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. Methodology – 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, pteros- tilbene 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. Conclusion – 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. Copyright © 2008 John Wiley & Sons, Ltd. Keywords: HPLC-UV-ESI/MS 2 ; polyphenols; hydroxystilbenes; hydroxyanthraquinones; Rheum rhaponticum; garden rhubarb Introduction Different species of the genus Rheum (Polygonaceae), such as R. palmatum L., R. emodi Wall. ex Meisn. and R. officinale Baill. are known for their high content of physiologically active hydroxy- anthraquinones (aloe-emodin, emodin, chrysophanol, rhein, physcion and their glycosides) in their roots (Okabe et al., 1973; Agarwal et al., 2000, Komatsu et al., 2006). On the other hand, a number of hydroxystilbenes and their derivatives have been identified in the rhizome of Korean rhubarb R. undulatum L. (Kashiwada et al., 1984; Ko, 2000; Matsuda et al., 2000a,b; Kageura et al., 2001), in the roots of R. maximowiczii Loinsk (Shikishima et al., 2001) and in the rhizome of R. emodi (Babu et al., 2004). More than 100 different phenolic compounds have either been identified or tentatively characterised in six rhubarb species (R. officinale, R. palmatum, R. tanguticum, R. franzenbachii, R. hotaoense and R. emodi) by their parent ion fragmentation spectra by Ye and co-authors (Ye et al., 2007). There is substantially less data in the literature on the content of phenolic compounds in the roots and especially in petioles of garden or dietary rhubarb R. rhaponticum L., which in many aspects is similar to R. undulatum. R. rhaponticum, the petioles of which are used as a food component, has been known in Chinese ethnopharmacology from ancient times. It has been shown that the rhizomes of this rhubarb contain hydroxystilbene rhaponticin (synonyms rhapontin and rhapontigenin glucoside), as well as its precursor trans-resveratrol (Rupprich et al., 1980). The latter is widely known for its versatile therapeutic potential (Piver et al., 2003; Baur and Sinclair, 2006). The physiological properties of resveratrol oligomers and related hydroxystilbenes have been much less studied. Resveratrol oligomers usually support the action of the monomer, but they may act also in a different manner (Piver et al., 2003). For example, it has been demonstrated that resveratrol oligomers strongly suppress HL-60 cell proliferation and induce DNA damage (Kang et al., 2003). Rhaponticin or rhapontin elicits antithrombotic and antiallergic properties (Park et al., 2002) and isorhapontigenin attenuates cardiac hypertrophy (Li et al., 2005). A special extract from the roots of R. rhaponticum, referred to as ERr 731® (trade name Phyto-Strol®, Carl Müller, Göppingen, Germany), has been regularly prescribed for climacteric com- plaints since 1993, and has been used in Germany for decades for women of child-bearing age suffering from oligomenorrhoea or amenorrhoea. According to recent investigations, the main active components in this extract are hydroxystilbenes (Möller et al., 2007; Wober et al., 2007). A limited number of references can be found concerning the determination of complex glycosides such as O-acetyl- or O-galloylglucosides of hydroxystilbenes or hydroxyanthraquinones in plants (Okasaka et al., 2004; Komatsu et al., 2006; Ye et al., * Correspondence to: A. Raal, Institute of Pharmacy, University of Tartu, Nooruse 1, 50411 Tartu, Estonia. E-mail: ain.raal@ut.ee a Department of Food Science and Hygiene, Estonian University of Life Sci- ences, Kreutzwaldi 58A, 51014 Tartu, Estonia b Institute of Pharmacy, University of Tartu, Nooruse 1, 50411 Tartu, Estonia