Flavonol determination

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). 

ENGELHARDT u H, FINGER A, HERZIG B and RUHR s (1992) Determination of flavonol glycosidees in black tea , Deutsche Lehensmittel-Rundschau, 88(3), 69-73. 

WANG H and HELLIWELL K (2001) Determination of flavonols in green and black tea leaves and green tea infusions by high-performance liquid chromatography , Foot/Res Intern, 34, 223-7. 

M. J. Dubber, V. Sewram, N. Mshicileli, G.S. Shephard and I. Kanfer, The simultaneous determination of selected flavonol glycosides and aglycones in Ginkgo biloba oral dosage forms by high performance liquid chromatography electrospray ionization mass spectrometry, J. Pharmaceut. Biomed., 37, 723 731 (2005). 

Michalkiewicz A, Biesaga M and Pyrzynska K. 2008. Solid-phase extraction procedure for determination of phenolic acids and some flavonols in honey. J Chromatogr A 1187( 1-2) 18-24. 

Sanchez-Morcno (2002) considered that this assay is an easy and accurate method for determining antioxidant capacity in fruit and vegetable samples. The DPPH assay has been used to determine the antioxidant activity of polyphenols (Sanchez-Moreno and others 1998 Bao and others 2004) flavonols (Jimenez and others 1998 1999 Choi and others 2002) anthocyanin-based natural colorants from berries (Espin and others... 

The potential health effects of anthocyanins and flavonols has stimulated much research in this area but, in view of the chemical complexity of the plant extracts, we are a long way from determining the chemical compounds responsible for the wide variety of claims. Regardless, a colorant with associated health benefits is a very desirable situation from an industry point of view. This is a very active research area. 

Flavonol truxinix esters with possible myorelaxant activity were determined in Pseudotsuga menziesii using various TLC stationary and mobile phases. Because of chemotaxonomical interest the same investigations were carried out on 34 species from the family of Pinaceae. Dried and pulverized needles were exhaustively extracted with chloroform followed with methanol. The chloroform fraction was evaporated to 5 ml and... 

Another isocratic elution method was applied for the determination of flavonols in green and black tea leaves and green tea infusions by RP-HPLC. The chemical structures of the flavonols studied are shown in Fig. 2.66. Infusions of teas were prepared by mixing lg of tea leaves with 100 ml of boiling water for 5min, then they have filtered and used for HPLC analysis. The infusion step was repeated three times. Flavonoids were hydrolysed by mixing lg of tea leaves with 40 ml of 60 per cent aqueous ethanol and 5 ml of 6 M HC1. The suspension was heated at 95°C for 2 h, then filtered and the volume was adjusted to 50 ml with 60 per cent aqueous ethanol. Separation was performed in an ODS column (150 X 4.6mm i.d.) operated at 30°C. The isocratic mobile phase consisted of 30 per cent aqueous ACN in 0.025 M KH2P04, and the pH was adjusted to 2.5 with 6 M HC1. The... 

More nsnal vegetables were stndied by Nnntila et al. [358] who characterized onions and spinach for the phenolic composition, with and without previous hydrolysis. The authors performed the simultaneous determination of phenolic acids, flavonols, flavones glycosides, and cathechins. Fignre 19.9 reprodnces the separation obtained for the standard mixture in this study. 

Since molecular weight information alone is insufficient for online structural determination of natural products, the fragmentation pathways of flavones and flavonols by fast-atom bombardment CID MS-MS have been documented. + ... 

Frison, S. and Sporns, P., Variation in the flavonol glycoside composition of almond seed coats as determined by MALDI-TOF mass spectrometry, J. Agric. Food Chem., 50, 6818, 2002. 

Fabre, N. et al.. Determination of flavone, flavonol, and flavanone aglycones by negative ion liquid chromatography electrospray ion trap mass spectrometry, J. Am. Soc. Mass Spectrom., 12, 707, 2001. 

A comprehensive and critical review of food flavonoid literature has led to the development of a food composition database for flavonols, flavones, procyanidins, catechins, and flava-nones. This database can now be used and continuously updated to estimate flavonoid intake of populations, to identify dietary sources of flavonoids, and to assess associations between flavonoid intake and disease. However, there is a need for better food composition data for flavones, procyanidins, and flavanones as current literature is sparse particularly for citrus fruits, fruit juices, and herbs. In addition, anthocyanin food composition data are lacking although validated methods of determination are becoming available. 

Escarpa, A., Perez-Cabrera, C., and Gonzalez, M.C., Optimization and validation of a fast liquid gradient for determination of prominent flavan-3-ols and flavonols in fresh vegetables, J. High Resolut. Chromatogr., 23, 637, 2000. 

Based on the currently available data, grape anthocyanin and flavonol profiles are determined by genetic characteristics whereas their content varies with the vine growing conditions. Available information still appears too limited and contradictory to draw any conclusion on the impact of genetic and environmental factors on grape proanthocyanidin composition. 

Mullen, W., Graf, B.A., Caldwell, S.T., Hartley, R.C., Duthie, G.G., Edwards, C.A., Lean, M.E., and Crozier, A., Determination of flavonol metabolites in plasma and tissues of rats by HPLC-radiocounting and tandem mass spectrometry following oral ingestion of [2- C]quercetin-4 -glucoside, J. Agric. Food Chem., 50, 6902, 2002. 

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