Effect of malvidin-3-monoglucoside on the browning of monomeric and dimeric flavanols
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The behaviour of (+)-catechin (cat), (–)-epicatechin (epi) and the procyanidin dimers B2 [epi-(4→8)-epi] and B3 [cat-(4→8)-cat], alone and in the presence of malvidin-3-monoglucoside, was studied in hydro-alcoholic solutions at pH 3.2 maintained at 32 °C for 120 days. Browning was observed both in the presence and absence of the anthocyanin, except in the solution containing only cat. The formation of pigments showing maximum absorption in the visible region of 440–460 nm was detected. The majority of these new pigments did not require the anthocyanin for their formation, but rather were derived directly from the flavanol. Nevertheless, some specific pigments showing similar spectra appeared in each of the solutions containing both a flavanol and the anthocyanin, and their production was attributed to a condensation process between the two latter compounds. The cat units showed a greater tendency to condense with the anthocyanin, while the epi units were more sensitive to chemical oxidation. The formation of pigments which showed maximum absorbance in the visible region around 530–545 nm, resulting from the condensation between the flavanol and the anthocyanin mediated by acetaldehyde, was also detected. As no acetaldehyde was added to the solutions, its presence was attributed to the oxidation of ethanol coupled to autoxidation of the catechol rings of the flavanols.
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