Light Stability of Vanillin Solutions in Ethanol

Abstract

Ethanolic solutions of vanillin, used as food flavouring are readily decomposed by the action of sunlight to 6,6′-dihydroxy-5,5′-dimethoxy-1,1′-biphenyl-3,3′-dicarbaldehyde (dehydrodi–vanillin). The decomposition is accompanied by the formation of a yellow colour and a slightly bitter taste. The U.S. Pharm–acopoeia (1975) spectroscopie assay of vanillin would be in–appropriate for samples contaminated with dehydrodivanillin, since the absorption maxima of vanillin are at 279 and 311 nm whereas the maxima for dehydrodivanillin are 279, 310nm with a shoulder at 337 nm.