Formation and Characterization of Polyphenol-Derived Red Chromophores. Enhancing the Color of Processed Cocoa Powders: Part 2

Very recently, we described the formation of (+)-catechin- and (−)-epicatechin-derived polar chromophores by means of a cocoa alkalization process. In this study we focus on the generation of unpolar chromophores using model reactions via Dutching with softer alkaline conditions. UPLC-HR-ESI-TOF-MS e analysis and one-dimensional and two-dimensional NMR spectroscopy led to the unequivocal identification of dehydrodicatechin- and hydroxyxanthene-derived chromophores. The previously unknown 6- C -linked constitutional isomers of C-6′B/C-6D-(2 R,3 S )-dehydrodicatechin ( 3, 5 ) were first described, and furthermore, the dimers dehydrocatechin-C-6′B/C-8D-(2 S,3 S )-epicatechin ( 2 ) and dehydrocatechin-C-6′B/C-6D-(2 S,3 S )-epicatechin ( 4, 6 ) as well as the reddish-colored chromophores 8- C -xanthenocatechin ( 7 ), 8- C -xanthenoepicatechin ( 8 ), 6- C -xanthenocatechin ( 9 ), and 6- C -xanthenoepicatechin ( 10 ) were identified as new compounds. A LC-MS/MS method was developed to screen and quantify both classes of chromophores as well as their precursors in alkalized cocoa powders. The dehydrocatechin dimers showed degradation via the alkalization process; in contrast, the xanthenocatechins highlighted an increase in concentration with stronger alkalization, and, therefore, contribute to cocoa reddening. These results, together with those previously published, give a clear insight into the chemistry of polyphenol-derived chromophores generated by cocoa powder alkalization and enable a better understanding of chromophore formation mechanisms toward a more comprehensive color design of cocoa powders.