Metabolism of Sulfur Dioxide in ‘Thompson Seedless’ Grape Berries

Abstract ‘Thompson Seedless’ grapes ( Vitis vinifera L.) were fumigated with 0.5% SO 2 at 0°C, and the amount of residual sulfite in the berries was followed over time. To prevent autooxidation during analysis, sulfite was stabilized using a solution of tetrachloromercurate-glycine, pH 10. After 72 hr, over 90% of the sulfite was oxidized to sulfate. Kinetics of sulfite loss indicate 2 different rates of loss, giving half-lives for sulfite of about 4 hr (70% of the total sulfite) and 20 hr (30% of the total sulfite). Presumably this reflects 2 forms, free and bound sulfite.