Formation and characterization of polyphenol-derived red chromophores: Enhancing the color of processed cocoa powders: Part 1

Although cocoa powder alkalization (Dutching) is a widely used industrial process to improve taste, dispersibility, and coloring of the final product, nevertheless knowledge about the compounds causing a change in coloring is fragmentary. By means of alkaline model reactions starting from the major cocoa polyphenol monomers, (+)-catechin or (−)-epicatechin, eight chromophores were derived from the first rearrangement product catechinic acid. LC-MS/MS analysis, one- and two dimensional-NMR, and electron paramagnetic resonance (EPR) spectroscopy led to the unequivocal identification of 6′-hydroxycatechinic acids (1a, 2a) and their radical states (1b, 2b), which were highlighted as main red chromophores. Six new dehydrocatechinic acid dimers (dehydrocatechinic acid-C-6′B/C-8D-(2R,3S)-catechin (3), dehydrocatechinic acid-C-6′B/C-6D-(2R,3S)-catechin (4, 5), dehydrocatechinic acid-C-6′B/C-8D-(2R,3R)-epicatechin (6), and dehydrocatechinic acid-C-6′B/C-6D-(2R,3R)-epicatechin (7, 8)) were also characterized as chr...