Isolation and Identification of Volatile Chemicals Formed in Aqueous L-Cysteine Solution with a UV Light

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Thirty-six volatile compounds were positively identified in the dichloromethane extract of an aqueous solution of L-cysteine that was irradiated with UV light at 253.7 nm for 24 hr. The irradiated solution was colorless but has a cooked meat-like flavor. The compounds identified were thiophenes, pyrazines, thiazoles, thiazolines, thiazolidines, and polymethylene sulfides. 2-Methylthiazole was found in the largest quantity, approximately 40% of the extract. Proposed photochemical reactions of cysteine included Strecker degradation, isomerization, dimerization, and homolytic fission of C-C, C-S, or S-H bonding.