Stress tolerance of the Saccharomyces cerevisiae adenylate cyclase fil1 (CYR1) mutant depends on Hsp26.

Fermentation-induced loss of stress resistance in yeast is an important phenotype from an industrial point of view. It hampers optimal use of frozen dough applications as well as high gravity brewing fermentations because these applications require stress-tolerant yeast strains during active fermentation. Different mutants (e.g. fil1, an adenylate cyclase mutant CYR1(lys1682)) that are affected in this loss of stress resistance have been isolated, but so far the identification of the target genes important for the increased tolerance has failed. Previously we have shown that neither trehalose nor Hsp104 nor STRE-controlled genes are involved in the higher stress tolerance of the fil1 mutant. The contribution of other putative downstream factors of the PKA pathway was investigated and here we show that the small heat-shock protein Hsp26 is required for the high heat stress tolerance of the fil1 mutant, both in stationary phase cells as well as during active fermentation.

Identification of lactic acid bacteria associated with traditional cachaça fermentations

During the production of traditional cachaça (alembicïs cachaça), contamination of the fermented must is one of the factors leading to economic losses in the beverage manufacturing industry. The diversity of bacterial populations and the role of these microorganisms during the cachaça production process are still poorly understood in Brazil. In our work, the fermentation process was followed in two distilleries located in the state of Minas Gerais. The objective of this work was to identify the populations of lactic acid bacteria present during cachaça fermentation using physiological and molecular methods. Lactic acid bacteria were isolated in high frequencies during all of the fermentative processes, and Lactobacillus plantarum and L. casei were the most prevalent species. Other lactic acid bacteria were found in minor frequencies, such as L. ferintoshensis, L. fermentum, L. jensenii, L. murinus, Lactococcus lactis, Enterococcus sp. and Weissella confusa. These bacteria could contribute to the increase of volatile acidity levels or to the production of compounds that could influence the taste and aroma of the beverage.

Identification of lactic acid bacteria associated with traditional cachaça fermentations.

During the production of traditional cachaça (alembic´s cachaça), contamination of the fermented must is one of the factors leading to economic losses in the beverage manufacturing industry. The diversity of bacterial populations and the role of these microorganisms during the cachaça production process are still poorly understood in Brazil. In our work, the fermentation process was followed in two distilleries located in the state of Minas Gerais. The objective of this work was to identify the populations of lactic acid bacteria present during cachaça fermentation using physiological and molecular methods. Lactic acid bacteria were isolated in high frequencies during all of the fermentative processes, and Lactobacillus plantarum and L. casei were the most prevalent species. Other lactic acid bacteria were found in minor frequencies, such as L. ferintoshensis, L. fermentum, L. jensenii, L. murinus, Lactococcus lactis, Enterococcus sp. and Weissella confusa. These bacteria could contribute to the increase of volatile acidity levels or to the production of compounds that could influence the taste and aroma of the beverage.

Selection, growth, and chemo-sensory evaluation of flocculent starter culture strains of Saccharomyces cerevisiae in the large-scale production of traditional Brazilian cachaça.

The physiological and kinetic capabilities of 233 Saccharomyces cerevisiae isolates, originating from traditional Brazilian cachaça fermentation, were evaluated under laboratory conditions to select flocculent and non-H2S producing strains to be employed in beverage production. Three flocculent S. cerevisiae strains were selected, two non-H2S producing and one H2S producing, and their kinetic performances were analysed during two large-scale fermentation experiments in a traditional cachaça distillery. One non-flocculent H2S-producing S. cerevisiae strain was also used for comparison with the flocculent strains. The results of mitochondrial DNA restriction analysis showed that the three flocculent starter S. cerevisiae strains, as well as the non-flocculent strain, remained in the process during the whole fermentation period, with cells numbering around 10(7) cfu/ml. All selected strains produced ethanol yields that were typically higher in the distillery than in the laboratory conditions, except for strain UFMGA-1240. The greatest diversity of non-Saccharomyces yeasts was observed prior to day 21 of cachaça fermentation; Pichia membranifaciens and Hanseniaspora guilliermondii were the most frequently isolated species. These yeasts were present in lower densities throughout the whole process. The cachaça produced by the selected strains contained concentrations of chemical compounds in accordance with current Brazilian legislation, and all cachaças scored well in sensory effective tests. In addition to the advantage of being flocculent, the strain UFMGA-1031 is non-H2S producing and also produces cachaça with good sensory acceptance. Therefore, this flocculent and non-H2S producing S. cerevisiae strain is highly suitable as a starter for production of high quality traditional cachaça.

Saccharomyces cerevisiae strains from traditional fermentations of Brazilian cachaça: trehalose metabolism, heat and ethanol resistance.

Nine indigenous cachaça Saccharomyces cerevisiae strains and one wine strain were compared for their trehalose metabolism characteristics under non-lethal (40 degrees C) and lethal (52 degrees C) heat shock, ethanol shock and combined heat and ethanol stresses. The yeast protection mechanism was studied through trehalose concentration, neutral trehalase activity and expression of heat shock proteins Hsp70 and Hsp104. All isolates were able to accumulate trehalose and activate neutral trehalase under stress conditions. No correlation was found between trehalose levels and neutral trehalase activity under heat or ethanol shock. However, when these stresses were combined, a positive relationship was found. After pre-treatment at 40 degrees C for 60 min, and heat shock at 52 degrees C for 8 min, eight strains maintained their trehalose levels and nine strains improved their resistance against lethal heat shock. Among the investigated stresses, heat treatment induced the highest level of trehalose and combined heat and ethanol stresses activated the neutral trehalase most effectively. Hsp70 and Hsp104 were expressed by all strains at 40 degrees C and all of them survived this temperature although a decrease in cell viability was observed at 52 degrees C. The stress imposed by more than 5% ethanol (v/v) represented the best condition to differentiate strains based on trehalose levels and neutral trehalase activity. The investigated S. cerevisiae strains exhibited different characteristics of trehalose metabolism, which could be an important tool to select strains for the cachaça fermentation process.