MICROWAVE-INDUCED VOLATILES OF THE MAILLARD MODEL SYSTEM UNDER DIFFERENT PH CONDITIONS

The volatile heterocyclic compounds produced from a D-glucose/L-cysteine browning model system by microwave irradiation were isolated and identified by gas chromatography and mass spectrometry. Microwave samples were prepared under different pHs. As the pH increased, the total volatiles generated also increased. A total of 22 compounds were identified. The major compounds formed at pH 2, 5, and 7 were furans, pyrroles, and thiophenes. At pH 9, the major compounds formed were oxazoles, pyrazines, thiazoles, pyranones, and furanones. The samples at pH 2, 5, and 7 had a pungent and sulfurous odor, whereas at pH 9 a nutty, meaty, and roasted aroma. 2-Methylthiazolidine was detected for the first time in a sugar/amino acid model system. The formation mechanism of 2-methylthiazolidine is proposed on the basis of the formation of a hemimercaptal intermediate at different pHs.