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

Michael Kofink,Rudolf Galensa,Menelaos Papagiannopoulos

doi:10.3390/12071274

Abstract

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 x L(-1) borate buffer (pH 8.5) with 12 mmol x L(-1) (2-hydroxypropyl)-gamma-cyclodextrin as chiral selector, a fused-silica capillary with 50 cm effective length (75 microm I.D.), +18 kV applied voltage, a temperature of 20 degrees 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 in unfermented, 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.

Highlights

In recent years the analysis of polyphenolic compounds in raw and processed food became more important with regard to their numerous physiological properties [1,2,3]
In comparison to the (-)-catechin levels, only small amounts of (+)-epicatechin would likely be formed during the epimerization reaction; (2) generally, the sensitivity of the detection used in capillary electrophoresis (CCE) is limited and the small amounts of (+)-epicatechin are not sufficiently separated from the close eluting predominant (-)-epicatechin peak; (3) the transoid structure of the substituents at C-2 and C-3 in catechin is thermodynamically favoured over the cisoid structure in epicatechin
Cocoa and chocolate samples were analyzed by CCE using the enantioseparation of catechin and epicatechin. (-)-Catechin was found among (-)-epicatechin and (+)-catechin as a result of an epimerization reaction. (+)-Epicatechin, could not be determined

Summary

Introduction

In recent years the analysis of polyphenolic compounds in raw and processed food became more important with regard to their numerous physiological properties [1,2,3]. High temperatures during the cocoa bean roasting process and the alkalization of the cocoa powder are the main factors inducing the epimerization reaction. The analysis of different samples of roasted cocoa beans and commercial cocoa products like chocolate provides evidence for the occurrence of (-)-catechin besides (-)-epicatechin and (+)-catechin (see Figures 3 and 4).

Results

Conclusion