(-)-Catechin in Cocoa and Chocolate: Occurence and Analysis of an Atypical Flavan-3-ol Enantiomer

Cocoa contains high levels of different flavonoids. In the present study, the enantioseparation of catechin and epicatechin in cocoa and cocoa products by chiral capillary electrophoresis (CCE) was performed. A baseline separation of the catechin and epicatechin enantiomers was achieved by using 0.1 mol·L−1 borate buffer (pH 8.5) with 12 mmol·L-1 (2-hydroxypropyl)-γ-cyclodextrin as chiral selector, a fused-silica capillary with 50 cm effective length (75 μm I.D.), +18 kV applied voltage, a temperature of 20°C and direct UV detection at 280 nm. To avoid comigration or coelution of other similar substances, the flavan-3-ols were isolated and purified using polyamide-solid-phase-extraction and LC-MS analysis. As expected, we found (-)-epicatechin and (+)-catechin inunfermented, dried, unroasted cocoa beans. In contrast, roasted cocoa beans and cocoa products additionally contained the atypical flavan-3-ol (-)-catechin. This is generally formed during the manufacturing process by an epimerization which converts (-)-epicatechin to its epimer (-)-catechin. High temperatures during the cocoa bean roasting process and particularly the alkalization of the cocoa powder are the main factors inducing the epimerization reaction. In addition to the analysis of cocoa and cocoa products, peak ratios were calculated for a better differentiation of the cocoa products

THE USE OF BIOSENSORS IN DETERMINATION OF DIFFERENT SUBSTANCES BY HIGH PERFORMANCE LIQUID CHROMATOGRAPHY

A rapid, simple and economic method was developed, which combines the specificity of enzymes with the high sensitivity of HPLC. Therefore sample pretreatment is reduced to simple dilution or extraction steps. In this work oxidases for alcohol, glucose, oxalic acid, ascorbic acid and galactose were immobilized and used as biosensors. Food samples were fruit juices and vegetable products, soft drinks and wine. The detection limit e.g. for oxalic acid was in the picomol range