Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/15/2001
Publication Date: 6/15/2001
Citation: Merken, H.M., Merken, C.D., Beecher, G.R. 2001. Kinetic method for the quantitation of flavonoids as aglycones in foods. Journal of Agricultural and Food Chemistry. 49(6):2727-2732. Interpretive Summary: Flavonoids, found in fruits, vegetables, botanicals, and teas, have shown great health benefits. The USDA is preparing to establish a data base of prominent flavonoids found in US foods, and add it to the current collection of publicly available data bases. Flavonoids are usually extracted from foods by acid. This same acid removes the attached sugars from the flavonoids ("deglycosylation"). However, the extracting acid often partially destroys the flavonoids over the course of the extraction, resulting in determinations of flavonoid concentrations which are really lower than they should be. While determining the optimal conditions for acidic extractions, a pattern emerged which is comparable to pseudo-first order kinetics. By extrapolating back to time zero, we can now mathematically determine the concentrations of flavonoids found in foods, even though the acid used to extract and deglycosylate the flavonoids destroys some of the flavonoids.
Technical Abstract: Flavonoid aglycones have often been quantitated after acidic hydrolysis. However, some flavonoids are destroyed by acid. We found that anthocyanidins can be deglycosylated and quantitated as their respective anthocyanidin aglycones using a kinetics method based on pseudofirst-order kinetics. Catechins, found as aglycones and gallate derivatives in nature, can be extracted neat and subsequently quantified. Flavanone glycosides and aglycones found in orange juice concentrate were highly unstable in acid solutions. However, neat extraction and subsequent chromatographic analysis of the few flavanone species in citrus foods is also possible. Flavone concentrations are stable in acid even after complete deglycosylation, so kinetics were not needed for quantitation of this subclass of flavonoids as aglycones.