White wine oxidation: The impact of iron(III) and organic acid photoactivity

The reaction of excessive amounts of molecular oxygen in wine can lead to deleterious compositional changes, including significant alteration of the sensory characteristics and loss of the main preservative (i.e., sulfur dioxide). The rate at which molecular oxygen reacts in wine is known to be influenced by a variety of parameters, one of which includes the exposure of the wine to UV-visible light. Several important photoactive components of wine are well reported (i.e., riboflavin and the iron(III) tartrate complex), however, little is known of the photoactivity of other iron(III) organic acid complexes under wine conditions, or the likely consequence of the products generated from such photoactivity on the colour and aroma characteristics of wine.This study utilises a combination of chromatographic analyses (UHPLC, ion exclusion â'' HPLCâ''MS/MS) to assess the impact of UV-visible light on aqueous ethanol solutions of iron in combination with tartaric acid, malic acid, succinic acid, lactic acid and citric acid. The main products generated as a consequence of photoactivity are described and the ability of the products to contribute to changes in wine colour and sulfur dioxide concentration is shown. The results demonstrate the importance of light to accelerate the consumption of oxygen in wine via iron / organic acid photochemistry, and show that the photoactivity of the combined iron(III) complexes can contribute to an array of products.