Kinetics method for the quantitation of anthocyanidins, flavonols, and flavones in foods.

Flavonoids are important dietary constituents owing to their health-promoting properties. As a result, simplified analytic techniques are required for the population of databases with food values so that associations between dietary intake and disease risk/incidence can be established. The current research provides a simplified sample preparation procedure for the accurate estimation of food anthocyanidins, flavones, and flavonols as aglycons. Traditionally, flavonoid aglycons have been formed by acidic hydrolysis. However, some flavonoid aglycons are slowly degraded by acid. A procedure has been developed whereby anthocyanidins and flavonols are deglycosylated with HCl in 50% aqueous methanol and the resulting aglycons subsequently quantified by application of pseudo-first-order kinetics to their degradation. Flavones are also deglycosolated under similar conditions but, at appropriate temperatures, their aglycons are stable in acid, so kinetics were not required for the quantitation of this subclass of flavonoids. Catechins and flavanones were rapidly degraded under the hydrolytic conditions used in these studies.

Liquid chromatographic method for the separation and quantification of prominent flavonoid aglycones.

Many beneficial health effects have been attributed to flavonoids, which are prevalent in plant-based foods. The literature is replete with chromatographic systems which are capable of measuring flavonoid content across one, two, and even three of the five common subclasses of flavonoids found in foods. However many foods and mixed diets, in particular, contain members of all five subclasses of flavonoids. We have developed an HPLC system for the separation and quantification of seventeen flavonoids, as their aglycones, which represent all five subclasses and are expected to be prominent in commonly consumed foods. Representative foods with significant concentrations of flavonoids from each of these subclasses were analyzed employing the new system.

Measurement of food flavonoids by high-performance liquid chromatography: A review.

The flavonoids are plant polyphenols found frequently in fruits, vegetables, and grains. Divided into several subclasses, they include the anthocyanidins, pigments chiefly responsible for the red and blue colors in fruits, fruit juices, wines, and flowers; the catechins, concentrated in tea; the flavanones and flavanone glycosides, found in citrus and honey; and the flavones, flavonols, and flavonol glycosides, found in tea, fruits, vegetables, and honey. Known for their hydrogen-donating antioxidant activity as well as their ability to complex divalent transition metal cations, flavonoids are propitious to human health. Computer-controlled high-performance liquid chromatography (HPLC) has become the analytical method of choice. Many systems have been developed for the detection and quantification of flavonoids across one, two, or three subclasses. A summary of the various HPLC and sample preparation methods that have been employed to quantify individual flavonoids within a subclass or across several subclasses are tabulated in this review.

Analysis of tea polyphenols.

Tea is the most highly consumed beverage in the world, other than water. However, unlike water, tea contains substantial amounts of polyphenols that have unique biological activities and may be responsible for many of the health benefits of tea. As a result, it is essential to be able to measure the various tea-associated polyphenols. Total polyphenol content is currently measured by using methodology based on reducing activity. Several HPLC systems with detectors that, collectively, have wide ranges in sensitivity have been developed for analysis of individual flavonoids in tea and biological samples, and for theaflavins in tea. Catechins also have been measured in plasma by solid phase extraction, addition of a chromophore, and colorimetric quantification. Except for theaflavins in tea, routine and robust methods for the measurement of polyphenol condensation products (dimers and thearubigens) in tea and biological samples have not been developed. Although in vitro and animal studies suggest substantial metabolism of flavonoids in the gastrointestinal tract, only a single HPLC procedure has been assembled for monitoring the metabolic products of quercetin in urine of human subjects.