Contribution to the identification of the pigments responsible for the browning of anthocyanin-flavanol solutions

Abstract

 The formation of pigments responsible for the browning of solutions of pH 3.2 containing malvidin-3-monoglucoside (Mv3g) and (+)-catechin (cat), stored at 32  °C, was studied by liquid chromatography with double detection by diode array spectrophotometry and mass spectrometry. The progressive accumulation of yellowish pigments, with λ_max in the visible region between 439 nm and 458 nm, was observed throughout the assay period. The results obtained allowed the hypothesis that these pigments result from anthocyanin-flavanol condensation to be discounted, and instead suggested that they derive from cat and involve products from the oxidation of ethanol and tartaric acid. Phloroglucinol, produced in the degradation of Mv3g, was seen to participate in the formation of one of the pigments. A colourless dimer resulting from the direct cat-Mv3g condensation was also found; this product was stable and did not evolve towards the formation of pigments during the period of the assay (90 days). Structures for the principal compounds detected were postulated, taking as a basis the data obtained from their mass spectra.