The major classes of plant pigments, excluding chlorophylls, are carotenoids, anthocyanins and betalains. Although carotenoids have been found in most flowering plants, betalains and anthocyanins have never been found in the same species, a phenomenon that is still a matter of debate. Here we investigate the occurrence of synergism between betalains, anthocyanins and carotenoids that could modify the properties of their mixtures compared to pure pigments. Red beetroot (Beta vulgaris, subs. vulgaris) juice was used as source of betanin (Bn) and betalamic acid; the later was coupled with L-proline in acidified water to produce indicaxanthin (BtP). These betalains were purified by RP-HPLC and characterized by HRMS and 1H NMR. A 2/1 w/w mixture of the anthocyanins cyanidin-3-glucoside and delphinidin-3-glucoside (Anth) was extracted from the shell of jabuticaba (Plinia cauliflora) fruits using a water/ethanol solution (30:70 v/v, pH 2), purified by Amberlite XAD7HP column chromatography and characterized by HPLC-DAD-HRMS(ESI+). Commercial samples of lutein in soybean oil were submitted to radial thin layer chromatography (SiO2, ethyl acetate:heptane (1:1 v/v)) and characterized by NMR spectroscopy. The combination of solutions of Bn, BtP, Anth and Lut in either water/DMSO or water/MeCN causes subtle changes in the absorption profiles compared to that of pure pigments. The effect of each component on the spectrofluorimetric response was analyzed by excitation-emission matrices combined with parallel factor analysis (EEM-PARAFAC). Changes in fluorescence quantum yield in mixtures were caused by optical filter effects. Cyclic voltammetry data combined to absorption spectroscopy was used to calculate the redox potentials of each compound in the electronically excited state. Results were rationalized with NMR spectroscopy and DFT calculations using BtP and 7-methoxy-4-methylflavylium as model compounds. The formation of a charge-transfer complex is proposed, which could explain the mutual exclusivity of these pigments in vivo.

Combination of plant pigments: Photophysical and redox consequences

2019 Spring National Meeting

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