Mechanism of formation of sulphur aroma compounds from L-ascorbic acid and L-cysteine during the Maillard reaction

摘要

The sulphur aroma compounds produced from a phosphate-buffered solution (pH 8) of L-cysteine and l-, l-[1-~(13)C] or l-[4-~(13)C] ascorbic acid, heated at 140 ± 2 ℃ for 2 h, were examined by headspace SPME in combination with GC-MS. MS data indicated that C-l of L-ascorbic acid was not involved in the formation of sulphur aroma compounds. The sulphur aroma compounds formed by reaction of L-ascorbic acid with L-cysteine mainly contained thiophenes, thiazoles and sulphur-containing alicyclic compounds. Among these compounds, 1-butanethiol, diethyl disulphide, 5-ethyl-2-methylthiazole, cis and trans-3,5-dimethyl-l,2,4-trithiolane, thieno[2,3-b]thiophene, thieno[3,2-b]thiophene, cis and trans-3,5-diethyl-1,2,4-trithiolane, 1,2,5,6-tetrathiocane, 2-ethylthieno[2,3-blthiophene, 2,4,6-trimethyI-l,3,5-trithiane and cyclic octaatomic sulphur (S_8) were formed solely by L-cysteine degradation, and the rest by reaction of L-ascorbic acid degradation products, such as hydroxybutanedione, butanedione, acetaldehyde, acetol, pyruvaldehyde and formaldehyde with L-cysteine or its degradation products, such as H_2S and NH_3. A new reaction pathway from L-ascorbic acid via its degradation products was proposed.