Abstract
Grape must or freshly pressed grape juice is a complex chemical matrix that impacts the efficiency of yeast fermentation. The composition of natural grape must (NGM) can be variable; thus, to ensure reproducibility, a synthetic grape must (SGM) with defined composition is commonly used. The aim of this work was to create conditions to advance the use of Saccharomyces cerevisiae laboratory strains for wine fermentation studies, considering previous results obtained for enological strains fermenting NGM under simulated winery conditions. We designed a new SGM formulation, ISA-SGM, by introducing specific modifications to a commonly used formulation, putting together previous reports. We added glucose and fructose in equal amounts (125 g/l) and 50 parts per million (ppm) sulfur dioxide (SO2, corresponding to standard enological treatment), and we optimized the concentrations of malic acid (3 g/l), citric acid (0.3 g/l), and tartaric acid (3 g/l). Using ISA-SGM, we obtained similar fermentative profiles for the wine strain ISA1000, the prototrophic strain S288C, and its auxotrophic derivative BY4741. In this case, the concentrations of supplements were optimized to 120 mg/l L-uracil, 80 mg/l L-methionine, 400 mg/l L-leucine, and 100 mg/l L-histidine. All these strains tested in ISA-SGM presented a similar fermentative performance as ISA1000 in NGM. ISA-SGM formulation is a promising new tool to allow the use of the auxotrophic BY strains in the detailed assessment of the alcoholic fermentation process under simulated winery conditions, and it provides a foundation to extract relevant physiological conclusions in future research on enological yeast traits.
Highlights
Saccharomyces cerevisiae plays a well-established and fundamental role in the complex process of winemaking
Strain S288C is a good laboratory model for white grape must fermentation Recently, we characterized the fermentative performance of an enological yeast strain (S. cerevisiae ISA1000) during fermentation of natural grape must (NGM) from the Portuguese white grape variety Arinto (Viana et al 2012)
We studied the behavior of the laboratory haploid yeast strain S. cerevisiae S288C in NGM, comparing fermentation parameters of this strain with those obtained for the enological yeast S. cerevisiae ISA1000 under the same conditions
Summary
Saccharomyces cerevisiae plays a well-established and fundamental role in the complex process of winemaking. The application of this strategy to wine strains has been impaired by the heterogeneity of industrial yeast genomes, which present frequently polyploidy or aneuploidy These genomes often display heterozygosity, single nucleotide polymorphisms, strain-specific open reading frames, and localized variations in gene copy number (Borneman et al 2011a,b; Bradbury et al 2006; Pretorius 2000). This variability makes it difficult to construct single mutant libraries and to complete whole-genome screening in these strains. A single-gene deletion library is currently being developed in a haploid derivative of a wine yeast (Tran et al 2010)
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