Influence of aeration on the physiological activity of flor yeasts.

The effect of periodic aeration on the physiological activity of a strain of Saccharomyces cerevisiae yeast during development of velum (flor) and biological aging of Sherry wine of the Fino type was investigated. L-Proline amino acid was the main nitrogen source for yeasts cells during the biological aging, and its exhaustion may be the cause of the production and consumption of other compounds that are involved in the aroma of wines. Aeration was found to increase adenylate energy charge, growth, and viability of the yeast cells. Also, it affected the intracellular redox equilibrium and the consumption and production of compounds including acetoin, acetaldehyde, higher alcohols, ethanol, glycerol, and acetic acid. Acetaldehyde reached its highest level after the second aeration, which coincided with the exhaustion of the nitrogen source in the medium. The enzyme activity of alcohol dehydrogenases I and II decreased immediately after each aeration, subsequently increasing once all of the dissolved oxygen in the wine had been consumed by yeast cells. Aldehyde dehydrogenase activity was detected only after the first aeration, and it may be related to the production and consumption of acetic acid in the wine.