Influence of L-cysteine on the formation of bitter-tasting aminohexose reductones from glucose and L-proline: identification of a novel furo[2,3-b]thiazine.

Thermal treatment of a 1 + 1 mixture of glucose and L-proline led to the development of an intense bitter taste being reflected in high amounts of the bitter-tasting bispyrrolidino- (1) and pyrrolidinohexose reductones (2) formed. Heating the reaction mixture in the presence of L-cysteine drastically reduced the amounts of these aminohexose reductones and, thereby, the intensity of the bitter taste. Studies on the mechanism of the cysteine-induced reduction of the bitter taste revealed that the precursor of the aminohexose reductones, the hexose-derived acetylformoin (3), reacted more easily with L-cysteine to form the 7-hydroxy-4a,6-dimethyl-2H,3H,4aH-furo[2,3-b]thiazine (4), a previousely unknown Maillard reaction product, than with L-proline to the aminohexose reductones 1 and 2, thereby blocking the formation of bitter-tasting compounds.