Characterization of precursors and elucidation of the reaction pathway leading to a novel coloured 2H,7H,8aH-pyrano[2,3-b]pyran-3-one from pentoses by quantitative studies and application of 13C-labelling experiments

The intensely coloured (1R,8aR)- and (1S,8aR)-4-(2-furyl)-7-[(2-furyl)methylidene]-2-hydroxy-2H,7H,8aH-pyrano[2,3-b]pyran-3-one (1a/1b) have recently been identified among the main coloured compounds formed in the presence of pentoses. To clarify its formation pathway, quantitative studies on the effectivity of certain carbohydrate degradation products as precursors of 1a/1b were performed indicating the 3-deoxypentose-2-ulose, furan-2-carboxaldehyde and hydroxyacetaldehyde as the penultimate precursors of the colourant. In addition, a labelling experiment with [13C1]-xylose was performed to elucidate how these precursors are transformed into 1a/1b.