Abstract
Sparkling wines elaboration has been studied by several research groups, but this is the first report on analysis of biological processes according to the Gene Ontology terms (GO terms) and related to proteins expressed by yeast cells during the second fermentation of sparkling wines. This work provides a comprehensive study of the most relevant biological processes in Saccharomyces cerevisiae P29, a sparkling wine strain, during the second fermentation under two conditions (without and with endogenous CO2 overpressure) in the middle and the end of second fermentation. Consequently, a proteomic analysis with the OFFGEL fractionator and protein identification with LTQ Orbitrap XL coupled to HPLC were performed. The classification of biological processes was carried out using the tools provided by the Saccharomyces Genome Database. Results indicate that a greater number of biological processes were identified under condition without CO2 overpressure and in the middle of the fermentation versus the end of the second fermentation. The biological processes highlighted under condition without CO2 overpressure in the middle of the fermentation were involved in the carbohydrate and lipid metabolic processes and catabolic and biosynthetic processes. However, under CO2 overpressure, specific protein expression in response to stress, transport, translation, and chromosome organization and specific processes were not found. At the end of fermentation, there were higher specific processes under condition without CO2 overpressure; most were related to cell division, growth, biosynthetic process, and gene transcription resulting in increased cell viability in this condition. Under CO2 overpressure condition, the most representative processes were related to translation as tRNA metabolic process, chromosome organization, mRNA processing, ribosome biogenesis, and ribonucleoprotein complex assembly, probably in response to the stress caused by the hard fermentation conditions. Therefore, a broader knowledge of the adaptation of the yeast, and its behavior under typical conditions to produce sparkling wine, might improve and favor the wine industry and the selection of yeast for obtaining a high-quality wine.
Highlights
The production of sparkling wine by the traditional, or Champenoise, method consists of two consecutive fermentations and a long period of aging of the wine in contact with the yeast lees
A first fermentation occurs, where the base wine is obtained from grape must, and a second fermentation of the base wine mixed with sugar and specific yeast strains of Saccharomyces occurs in a sealed bottle
On the other hand, during yeast selection, early cell death and autolysis are wanted to accelerate the process of elaboration of sparkling wines.During the second fermentation, yeasts are subjected to various stress factors, such as high ethanol content, nitrogen deficiency, low pH values, low temperature, and CO2 overpressure [14]
Summary
The production of sparkling wine by the traditional, or Champenoise, method consists of two consecutive fermentations and a long period of aging of the wine in contact with the yeast lees. Once yeast cells die during aging, intracellular compounds are released to the wine as mannoproteins during the autolysis process, improving the quality, and favoring the organoleptic properties of these special wines [11,12] During these stages, the yeast is subjected to various stresses, so ensuring its survival and tolerance to these conditions is essential to guarantee the success of the sparkling winemaking process [13]. Since there are few researches focused on analysis of biological processes according to the Gene Ontology (GO) terms under fermentation conditions, the present work aims to study the effect of endogenous CO2 overpressure, released by Saccharomyces cerevisiae P29 strain, on the proteins related to the GO terms of sparkling wines elaborated according to the Champenoise method. Broader knowledge about the adaptation of the yeast and its behavior under the typical conditions of the second fermentation would improve the industrial process, and favor the selection and genetic improvement of wine yeast strains capable of carrying out this process, giving rise to a wine of quality
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