Change in Kinetic parameters of commercial yeast in the presence of copper fungicides

Abstract

The Serra Gaucha has a high rainfall occurrence during the ripening and harvest. It results in higher use of fungicides, being the copper-based ones, the most commonly used. High levels of this metal can cause stress to the yeast, thus, influencing on the fermentation kinetics. The aim of this study was to evaluate the fermentative behavior of oenological yeast in the presence of copper content in the must. The experiment used the following fungicides: Copper Sulfate, Copper Oxychloride and Copper Hydroxide. Samples were inoculated with S. cerevisiae, S. cerevisiae var. bayanus and Torulaspora delbrueckii and the fermentation was plotted for carbon dioxide production by time. The fermentative kinetics were assessed by the following kinetic parameters: the lag phase time, maximum rate of CO2 production and maximum production of CO2. The study showed that T. delbrueckii had higher sensitivity to copper regarding the lag phase. Copper oxychloride promoted greater latency period in yeast T. delbrueckii and S. cerevisiae. All copper fungicides decreased maximum rate of fermentation, and T. delbrueckii was the most affected. The maximum CO2 production during the fermentations significantly differed only in the presence of copper sulphate.