title: Feasibility of measuring ferricyanide reduction by yeasts to estimate their activity during alcoholic fermentation in wine-making conditions.
abstract: We assessed the feasibility of measuring the extracellular reduction of ferricyanide in the presence of an intermediate carrier (menadione) as a means of estimating the activity of yeasts during alcoholic fermentation. A spectrophotometric and a potentiometric approach were used. Comparison of specific reductase activity and gas production rate during the stationary phase indicated that measuring the menadione-catalyzed reduction of ferricyanide provides a good estimate of the total activity of the yeast cells in a fermenting must. The response observed following the addition of an electron acceptor (acetaldehyde) confirmed that the reductase activity of menadione is dependent on the availability of NADH. The stability of menadione in the fermentation medium, as assessed by the potentiometric method, suggested that electrochemical reoxidation of the ferrocyanide can act as a substitute for the addition of an electron acceptor when studying the redox regulation of fermenting yeasts.
authors.affiliation: Unité Mixte de Recherche (UMR), Sciences pour l'oenologie, Institut National de la Recherche Agronomique (INRA), 2 place Viala, 34070 Montpellier Cedex 1, France.
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Roustan
authors.forename: Jean-Marie
authors.initials: JM
authors.lastname: Sablayrolles