Chemical Profiling and Quantification of Isoflavone Phytoestrogens in Kudzu Using LC/UV/MSD

Abstract

Method development for determination of isoflavones in kudzu was achieved by HPLC/UV/ESI-MSD. Us- ing three kudzu species of Pueraria lobata, P. thomsonii and P. edulis, and analyzing the isoflavones sepa- rately by species and from different plant tissues (roots, stems, leaves, flowers and fruits) in each species, a total of 25 isoflavones were identified by their molecular ions and characteristic fragment ion peaks using LC/MSD under MS and MS/MS mode, and in comparison with standard isoflavones. Two main chemical groups were identified: 1) 8-C-glycosyl isoflavone of puerarin and the analogues of 5-OH puerarin, 3’-OH puerarin, 3’-OMe puerarin, and their glycosides; and 2) daidzein, genistein, glycitein and their glycosyl and malonyl derivatives, which are similar to those known in soy. To accurately quantitate total isoflavones, acidic hydrolysis during extraction of kudzu samples was applied to convert the oxygen glycosides into their respective isoflavone aglycones of daidzein, genistein and glycitein, or non-hydrolyzed carbon glycosides of puerarin, 5-OH puerarin, 3’-OH puerarin and 3’-OMe puerarin. Under the multiple optimized conditions, all seven isoflavones in acidic hydrolyzed kudzu extracts were successfully separated within 30 min and quanti- fied individually with calycosin used as internal standard by both UV and MS detectors. For the quantitative study, several standards e.g. 5-OH puerarin, 3’-OH puerarin and 3’-OMe puerarin are not commercially available. Using polyamide, sephdex-LH20 chromatography and Prep-HPLC, we purified these three stan- dards from kudzu extracts and then elucidated their structures by UV, MS and NMR spectrometric methods. This is the first method to simultaneously quantitate all the isoflavones in kudzu.