Photoinduced generation of 2,3-butanedione from riboflavin.

The volatile compound formation from riboflavin solution of a phosphate buffer (0.1 M, pH 6.5) under light for 15 h was studied by SPME-GC and SPME-GC/MS analysis. Only one major compound in the riboflavin solution was formed and increased as the light exposure time increased. The light-exposed riboflavin solution had a buttery odor. The compound of riboflavin solution under light was analyzed by gas chromatography and olfactometry. The major volatile compound eluted from the gas chromatograph had a buttery odor. The buttery odor compound was positively identified as 2,3-butanedione by a combination of gas chromatographic retention time, mass spectrum, and odor evaluation of authentic 2,3-butanedione. The addition of sodium azide, a singlet oxygen quencher, to riboflavin solution minimized the formation of the buttery odor compound. Singlet oxygen was involved in the formation of the buttery odor. The 2,3-butanedione was produced from the reaction between riboflavin and singlet oxygen. Singlet oxygen was formed from triplet oxygen by riboflavin photosensitization mechanism. This is the first reported oxidation reaction between riboflavin and singlet or triplet in food and biological systems.