Despite the key role of flavan-3-ols in many foods, very little is yet known concerning the modification of their chemical structures through food processes. Degradation of model media containing (-)-epicatechin and procyanidin B2, either separately or together, was monitored by RP-HPLC-DAD-ESI(-)-MS/MS. Medium composition (aqueous or lipidic) and temperature (60 and 90 °C) were studied. In aqueous medium at 60 °C, (-)-epicatechin was mainly epimerized to (-)-catechin, but it was also oxidized to "chemical" dimers, a "chemical" trimer, and dehydrodi(epi)catechin A. Unlike oxidation, epimerization was enhanced at 90 °C. In lipidic medium, epimerization proved slow but degradation was faster. Procyanidin B2 likewise proved able to epimerize, especially at 90 °C and in aqueous medium. At high temperature only, the interflavan linkage was cleaved, yielding the same compounds as those found in the monomer-containing model medium. Oxidation to procyanidin A2 was also evidenced. With little epimerization and slow oxidation even at 90 °C, procyanidin B2 proved more stable in lipidic medium. Synergy was also observed: in the presence of the monomer, the dimer degradation rate increased 2-fold at 60 °C. This work states for the first time the presence of newly formed flavan-3-ol oligomers in processed cocoa.

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Fresh, ripe cocoa beans from Cameroon (German cocoa/Amelonado group and ICS 40/Trinitario group) were subjected to fermentation-like incubations in acetic acid, lactic acid, or both and to natural fermentation. Two naturally fermented samples from Cuba (UF 654/Trinitario group and C 411/Criollo group) were also investigated. Both cyanidin-3-galactoside and cyanidin-3-arabinoside (found as major anthocyanins in colored beans only) were drastically degraded through fermentation, especially in small beans and in the presence of acetic acid. On the other hand, emergence of a cyanidin-rhamnose isomer was evidenced, even in Criollo beans. In addition to the recently described structures F1 and F2 [m/z = 575 in ESI(-)], three additional polyphenolic structures [F3, F4, and F5; m/z = 557 in ESI(+)] were found after fermentation, the two former ones resulting from epicatechin oxidation. Synthesis of F5 requires an interclass reaction between cyani(di)n and epicatechin, which explains its absence in fermented Criollo beans.

Cocoa is known as an important source of flavan-3-ols, but their fate "from the bean to the bar" is not yet clear. Here, procyanidin A2 found in native cocoa beans (9-13 mg/kg) appeared partially epimerized into A2 through fermentation, whereas a second epimer (A2) emerged after roasting. At m/z 575, dehydrodiepicatechin A was revealed to be the major HPLC peak before fermentation, whereas F1, a marker of well-conducted fermentations, becomes the most intense after roasting. RP-HPLC-ESI(-)-HRMS/MS analysis performed on a procyanidin A2 model medium after 12 h at 90 °C revealed many more degradation products than those identified in fermented cocoa, including the last epimer of A2, A2 open structure intermediates (m/z 577), and oxidized A-type dimers (m/z 573).

The degradation rate of flavan-3-ols through roasting is higher in cocoa beans containing anthocyani(di)ns. The liberation of a pool of (-)-catechin when submitted to roasting at 150 °C allows to distinguish white-seeded cultivars. © 2017 Society of Chemical Industry.