Characterisation of novel 1 H ,4 H -quinolizinium-7-olate chromophores by application of colour dilution analysis and high-speed countercurrent chromatography on thermally browned pentose/ L -alanine solutions

Abstract

Thermal treatment of aqueous solutions of xylose and L-alanine at pH 5.0 resulted in the formation of various coloured compounds, which were ranked according to their colour impactsby application of the recently developed colour dilution analysis. High-speed countercurrent chromatography was then successfully used for the first time to isolate colour-intense reaction products from complex Maillard mixtures, amongst which the structures of 2-[(2-furyl)methylidene]-4-hydroxy-5-methyl-2H-furan-3-one (1), and of the novel compounds 3-(2-furyl)-8-[(2-furyl)methyl]-4-hydroxymethyl-1-oxo-1H,4H-quinolizinium-7-olate (2) and 3-(2-furyl)-8-[(2-furyl)methyl]-4,5-bis(hydroxymethyl)-1-oxo-1H,4H-quinolizinium-7-olate (3) were determined by LC/MS, 1D and 2D NMR as well as UV/Vis spectroscopy. To measure the contribution of these colorants to the overall colour of the browned Maillard mixture, colour activity values were calculated as the ratio of the concentration to the visual detection threshold of each colorant. By application of this colour activity concept, 2.2% of the total colour of the thermally browned xylose/L-alanine solution was shown to be covered by the novel 1H,4H-quinolizinium-7-olate chromophores 2 and 3.