Aglycones identification

As relatively few standard compounds are available from commercial or other sources, identification of flavonol glycosides has to be achieved by alternative means, for example UV-, H- and C-NMR spectroscopy. Therefore hydrolysing all glycosides to aglycones followed by HPLC determination offers a practical method for the quantitative determination of flavonoids in tea (Hertog et al, 1993a Wang and Helliwell, 2001). 

Knowledge of the identity of phenolic compounds in food facilitates the analysis and discussion of potential antioxidant effects. Thus studies of phenolic compounds as antioxidants in food should usually by accompanied by the identification and quantification of the phenols. Reversed-phase HPLC combined with UV-VIS or electrochemical detection is the most common method for quantification of individual flavonoids and phenolic acids in foods (Merken and Beecher, 2000 Mattila and Kumpulainen, 2002), whereas HPLC combined with mass spectrometry has been used for identification of phenolic compounds (Justesen et al, 1998). Normal-phase HPLC combined with mass spectrometry has been used to identify monomeric and dimeric proanthocyanidins (Lazarus et al, 1999). Flavonoids are usually quantified as aglycones by HPLC, and samples containing flavonoid glycosides are therefore hydrolysed before analysis (Nuutila et al, 2002). 

As we have seen above, anthocyanins comprise an aglycone fraction commonly known as anthocyanidin and a frequently acylated osidic substituent. This characteristic leads to two different approaches for the analysis of these pigments (1) a direct anthocyanin analysis without a hydrolysis stage requiring identification of a number of molecules (several hundreds in the plant kingdom) or (2) an analysis of the anthocyanidin fraction only after hydrolysis of the anthocyanins present in the medium. 

S. Hakkinen and S. Auriola, High performance liquid chromatography with electrospray ioniza tion mass spectrometry and diode array ultraviolet detection in the identification of flavonol aglycones and glycosides in berries, J. Chromatogr. A, 829, 91 100 (1998). 

Identification of flavonoids Quantification of individual flavonoids depends heavily on the availability of standard references. Only a limited number of common flavonoids are commercially available as standards. Standard references for flavonoid glycosides are particularly difficult to find thus direct quantification of the native glycosides is nearly impossible. Analysis of the aglycones after acid or enzymatic hydrolysis is therefore common practice. When standard flavonoids are not available, or when unknown compounds are encountered in a particular fruit or vegetable, use of a DAD... 

It was stated that this combined technique (HPLC-DAD, HPLC-ESI-MS, GC-MS) allows the safe identification of flavonol aglycones and glycosides and can be used for the analysis of these compounds in berries [161]. 

S.M. Boue, C.H. Carter-Wientjes, B.Y. Shih and T.E. Cleveland, Identification of flavone aglycones and glucosides in soybean pods by liquid chromatography-tandem mass spectrometry. J. ChromatogrA 991 (2003) 61-68. 

J. Qu, Y. Wang, G. Luo and Z. Wu, Identification and determination of glucuronides and their aglycones in Erigeron breviscapus by liquid chromatography-tandem mass spectrometry. J. Chromatogr.A 928 (2001) 155-161. 

There have been many survey studies of citrus flavonoids, yet by no means has an exhaustive analysis been performed for all species and cultivars. Surveys often are initiated by hydrolysis of tissue extracts and identification of the flavonoid aglycones present in the tissues. This provides a basis for subsequent identification of the glycosylated compounds present... 

Identification of the Aglycone Moiety of the L, floccosa Glucosinolate with m/z 424... 

Spiked standards recovery reported, identification on aglycone RP-HPLC retention times mg/kg fresh weight Accept... 

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