Photodegradation of organic acids in a model wine system containing iron

UV-visible light has previously been shown to greatly accelerate the degradation of tartaric acid in model wine solutions containing iron, resulting in the production of glyoxylic acid. In this study, model wine solutions containing tartaric acid, malic acid, succinic acid, citric acid or lactic acid, as well as iron, were exposed to light at wave lengths above 300 nm or stored in darkness. All the organic acids were partially degraded in the samples exposed to light, but were stable in the samples stored in darkness. The photodegradation products identified using ion-exclusion liquid chromatography with diode array and mass spectrometry detection included a number of aldehydes and ketones. Glyoxylic acid and 2,3-dioxopropanoic acid were derived from tartaric acid, 3-oxopropanoic acid from malic acid and succinic acid, 1,3-acetonedicarboxylic acid and acetoacetic acid from citric acid and acetaldehyde from lactic acid. Possible pathways for the formation of these compounds are discussed. In addition, the potential implications of these reactions in white wine are described.