Analysis of catechins in Theobroma cacao beans by cyclodextrin-modified micellar electrokinetic chromatography

A micellar electrokinetic chromatography (MEKC) method was developed for the quantitation of polyphenols (+)-catechin and (-)-epicatechin (catechin monomers) and the methylxanthine theobromine in Theobroma cacao beans. Owing to the poor stability of catechin monomers in alkaline conditions, a 50 mM Britton-Robinson buffer at a pH 2.50 was preferred as the background electrolyte. Under these conditions, the addition of hydroxypropyl-beta-cyclodextrin (HP-beta-CD) at a concentration of 12 mM to the SDS micellar solution (90 mM), resulted in a cyclodextrin-modified micellar electrokinetic chromatography (CD-MEKC) endowed with two peculiar advantages compare to the conventional MEKC: (i) strong improvement of separation of the most important phytomarkers of T. cacao and (ii) enantioselectivity toward (+/-)-catechin. In particular, separation of methylxanthines (theobromine and caffeine), procyanidin dimers B1 and B2, and catechins (epicatechin and catechin) was obtained simultaneously to the enantioseparation of racemic catechin within 10min. The enantioselectivity of the method makes it suitable in evaluation of possible epimerisation at the C-2 position of epicatechin monomer potentially occurring during heat processing and storage of T. cacao beans. The extraction procedure of the phytomarkers from the beans was approached using ultrasonic bath under mild conditions optimized by a multivariate strategy. The method was validated for robustness, selectivity, sensitivity, linearity, range, accuracy and precision and it was applied to T. cacao beans from different countries; interestingly, the native enantiomer (+)-catechin was found in the beans whereas, for the first time we reported that in chocolate, predominantly (-)-catechin is present, probably yielded by epimerisation of (-)-epicatechin occurred during the manufacture of chocolate.