Role of carbonyl compounds in SO2 binding phenomena in musts and wines from botrytized grapes

Carbonyl compounds play an important role in musts from botrytized grapes. Some of them, such as glyoxal and methylglyoxal, may explain a considerable part of bindable SO2. Others, such as 2- and 5-oxogluconic acids, produced by gluconic acid oxidation in proportions respectively from 2.5 per 1 play an interesting role as SO2 binding indicator. Finally, the levels of some compounds such as dihydroxyacetone, 5-oxofructose, and delta-gluconolactone in balance with gluconic acid are well correlated with SO2 binding powers and also explain a large part-of the bindable SO2 in musts. During alcoholic fermentation, only dihydroxyacetone among these three compounds is metabolized by yeast. Thus, two compounds present in grapes, delta-gluconolactone and 5-oxofructose, with three yeast SO2-binding byproducts, ethanal, pyruvic, and 2-oxoglutaric acids, explain much of the SO2 binding power in wines from botrytized grapes.