Redox effect on volatile compound formation in wine during fermentation by Saccharomyces cerevisiae.

Although redox state is a well-known key process parameter in microbial activity, its impact on wine volatile aroma compounds produced during fermentation has not been studied in detail. In this study we report the effect of reductive and microaerobic conditions on wine aroma compound production using different initial amounts of yeast assimilable nitrogen (YAN: 180 and 400 mg N/l) in a simil grape must defined medium and two S. cerevisiae strains commonly used in wine-making. In batch fermentation culture conditions, reductive conditions were obtained using flasks plugged with Muller valves filled with sulphuric acid; while microaerobic conditions were attained with defined cotton plugs. It was found that significant differences in redox potential were obtained using the different plugs, and with variation of over 100 mV during the main fermentation period. Significant differences in the final concentration of higher alcohols, esters and fatty acids were attributed to differences in the redox state in the medium in both strains. A consistent increase in esters and medium chain fatty acids, as well as a decrease of higher alcohols and isoacids, was seen under reductive fermentation conditions. Interestingly, 1-propanol, δ-butyrolactone and ethyl lactate concentrations, showed no significant variation under the different redox conditions. A better understanding of the influence of redox state of the fermentation medium on the composition of volatile compounds in wine could enable improvement of vinification management. From a microbiological standpoint results presented here will contribute to the standardization of data models for the application of metabolic footprinting methods for wine yeast strain phenotyping and characterization.