Epicatechins analysis

The chemical characteristics of the proanthocyanidins were elucidated by total oxidation and partial degradation in the presence of phloroglucinol followed by HPLC analysis. The native extract of proanthocyanidins contained (+) gallocatechin, (-) epigallocatechin, (h-) catechin, and (-) epicatechin units. ... 

Another study employed a similar RP-HPLC method for the determination of trails- and d.v-rcsvcratrol, catechin, epicatechin, quercetin and rutin in wines and musts. Wine samples were filtered and diluted when necessary and used for analysis without any other pretreatment. Separation was performed in an ODS column (150 X 4 mm i.d. paricle size 5 71m) at ambient temperature. The gradient began with ACN-5 per cent aqueous acetic acid (9 91, v/v) for 0-10 min to 25 75 in 1 min hold for 11 min to 70 30 in 1 min, hold for 5 min. The flow rate was 1 ml/min. Analytes were detected by DAD. Fluorescence detection used 280/315 nm (excitation/emission) for catechin and epicatechin 314/370 nm for fims-resveratrol and 260/370 nm for d.v-rcsvcratrol. Chromatograms of a red wine sample obtained at different... 

HPLC separation, as described above, is restricted to rather simple compounds that represent only a small proportion of flavonoids. Indeed, proanthocyanidin analysis becomes increasingly difficult as their molecular weight increases, due to the larger number of possible structures, smaller amounts of each individual compound, and poorer resolution of the chromatographic profiles. This is especially true of grape proanthocyanidins, which, unlike those of apple or cacao consisting only of epicatechin units, are based on four major... 

Polymeric fractions were obtained from wines, seed and skin extracts by fractionation on a Toyopearl HW-40 column as described by Souquet et al (4). Two aliquots of the fractions containing polymeric material were t en to dryness under vacuum. The first one was used to determine proanthocyanidin composition by thiolysis followed with HPLC analysis (17). The other one was dissolved in MeOH acidified with 2% HCl and used to estimate the concentration of total polymeric polyphenols and polymeric pigments by measuring the absorbance, respectively at 280 nm and 530 nm. Absorbance data were converted to equivalent epicatechin and equivalent malvidin-3-glucoside, respectively, using the extinction coefficients determined for each compounds under similar conditions. 

HPLC analysis can be performed by direct injection of the tartrate buffer extract. The chromatographic peaks of catechin and epicatechin are well resolved, but an overlapping of procyanidins and epicatechin gallate with other compounds, may occur. To improve the separation among them, a fractionation of the sample on a C18 cartridge can be performed 5 mL of extract are added of 15 mL H2S04 5 x 10 3M and passed... 

Figure 2.19 Chromatogram relative to analysis of monomer catechins in the skins extract (fraction diethyl ether from Ci8 cartridge) (sample volume injected lOp-L). 1. (+)-catechin, 2. (—)-epicatechin...

Although phospholipid bilayers are better mimics of biomembranes than are micelles, there are few reliable quantitative data on flavonoid antioxidant activities in lipid bilayers. Terao and coworkers compared the antioxidant efficiency of quercetin and catechins (epicatechin and epicatechin gallate) with that of a-Toc in egg yolk PC liposomes using initiation by the water-soluble initiator, ABAP, and analysis of hydroperoxide formation and antioxidant consumption by HPLC. Based on the length of the induction periods and the profile of suppressed hydroperoxide formation, they concluded that quercetin and the catechins were more efficient antioxidants than a-Toc in these bilayers. Apparently the unique behavior of a-Toc in bUayers is responsible for these results (vide supra). In hexane and alcohols solution during suppressed peroxidation of methyl linoleate, the relative antioxidant activities reversed so that the flavonoids were 5-20 times less active... 

SPE on a CLX cartridge was applied to separate acidic phenols such as chlorogenic acid (95) from neutral phenols such as (—)-epicatechin (2), (+)-catechin (3), phloridzin (96) and quercitrin (100). The neutral phenols were determined in apple juice by capillary LC with UVD at 280 nm, as an alternative to conventional HPLC. LOD were from 9 pg for 96 to 97 pg for 3. HPLC analysis with MS and DA-UVD showed that apple pomace is a good potential source for phenoUcs. The usefulness of arbutin (9) as specific marker for pear products was placed in doubt (see Section II.A °). 

A simple CZE method, using a borate buffer at pH 9.5 and UVD at 280 nm, was applied for analysis of Spanish red wines. Although the electrophoretic profile was similar for different wines, the quantitative analysis varied much between them. The following phenolic components were identified (—)-epicatechin (2), (+)-catechin (3), (—)-epigallocatechin (74), syringic acid (70), vanillic acid (38), gallic acid (8), protocatechuic... 

Reactions taking place in a model solution containing malvidin 3-0-glucoside, (-)-epicatechin and acetaldehyde was explored by HPLC/DAD and HPLC/ESI-MS analysis 29). Acetaldehyde is a product of yeast metabolism but may also result from ethanol oxidation or from decarboxylation of pyruvic acid during fermentation of grapes (43). 

HPLC-ESI-MS analysis of the mixture conducted in the positive ion mode showed the presence of both ethyl-linked flavanol dimers, detected at m/z 607 amu, and ethyl-linked adducts involving both (-)-epicatechin and the... 

Heimdal H, Bro R, Larsen LM, Poll L, Prediction of polyphenol oxidase activity in model solutions containing various combinations of chlorogenic acid, (—)-epicatechin, 02, C02, temperature and pH by multiway analysis, Journal of Agricultural and Food Chemistry, 1997, 45, 2399-2406. 

FIGURE 8.12 Proposed scavenging mechanism of epicatechin and catechin to 2,2-diphenyl-l-picrylhydrazyl. (From Sang, S., Cheng, X., Stark, R. E., Rosen, R. T., Yang, C. S., and Ho, C.-T. 2002. Chemical studies on antioxidant mechanism of tea catechins Analysis of radical reaction products of catechin and epicatechin with 2,2-diphenyl-l-picrylhydrazyl. Bioorg. Med. Chem. 10 2233-37. With permission.)... 

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