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-2 H,3 H,4a H -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.