In vitro specific activities of alcohol and aldehyde dehydrogenases from two flor yeasts during controlled wine aging

Two flor yeast strains of Saccharomyces cerevisiae (S. cerevisiae strains capensis and bayanus) which form velum on the surface of sherry wine during biological aging have been used. Aldehyde and alcohol (isoenzymes I and II) dehydrogenases were detected in vitro during the entire wine-aging process in the flor yeast strains. All enzymatic activities decreased during the first 155 days of wine aging, and after this period, an increase was observed. Ethanol consumption in the wine and the specific activity of alcohol dehydrogenase I were independent of the S. cerevisiae strain. The greater activity of alcohol dehydrogenase II is directly related to the higher acetaldehyde production by S. cerevisiae race bayanus in the wine. This strain has a slower and prolonged growth in the flor film, which permits a continued accumulation of acetaldehyde in the wine. The higher activity of aldehyde dehydrogenase in capensis-strain during the flor formation may be related to the production and consumption of large amounts of acetic acid, which involved a more abundant and accelerated cellular growth. We suggest that part of the acetaldehyde might be converted into ethanol during wine aging by alcohol dehydrogenase I in order to maintain a normal redox balance.