Fermentation kinetics and copper adsorption capacity of commercial Saccharomyces and non-Saccharomyces yeasts

Abstract

The extensive utilisation of copper-based fungicides in viticulture has resulted in the progressive accumulation of copper in vineyard soils and grape, and, consequently in must, raising concerns about its impact on yeast performance, fermentation efficiency, wine quality, and consumer safety. Substantial copper concentrations can inhibit yeast metabolism and modify fermentation kinetics, thereby potentially impacting the sensory profile of wine. The selection of yeast strains capable of adsorbing copper represents a sustainable biotechnological alternative to conventional chemical approaches. This study evaluated the fermentation performance and copper removal capacity of 15 commercial yeast strains, in addition to two control strains with known high and low copper adsorption capacities. The microbiological dynamics of Saccharomyces and non-Saccharomyces populations were monitored by plate counts. Fermentation trials were conducted in a modified YPD medium containing 30 ppm of CuSO₄·5H₂O and in grape musts supplemented with the same concentration for microfermentations. Growth behaviour, lag phase duration, and fermentation vigour were evaluated through the analysis of growth curves and CO₂ related weight loss measurements. During the initial phases of fermentation (24, 48, and 72 hours), the different strains exhibited distinct growth kinetics, with development profiles that were, in general, consistent with the inoculation concentration. In other cases, microbial counts increased progressively to 7.5–8.0 Log CFU/mL. Growth in modified YPD exhibited various adaptation patterns: some strains rapidly entered the log phase (10–13 h), whereas others showed an extended lag phase (20–27 h) before initiating robust growth. Fermentation progress, measured via CO₂ weight loss, revealed notable differences in both lag and log phases among the strains. The release of CO₂ within the first 48 hours of fermentation was shown to be a reliable predictor of the final fermentation vigour. ICP-OES quantification of residual copper showed a significant decrease from the initial concentration, with most samples reaching low final levels. Even if copper removal efficiency was strain-dependent, all strains demonstrated tolerance to high copper concentrations adopted, maintained active fermentation and significantly decreased residual copper. These finding confirm their potential for robust and sustainable applications in industrial-scale fermentation processes.

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