Stress Resistance and Adhesive Properties of Commercial Flor and Wine Strains, and Environmental Isolates of Saccharomyces cerevisiae

Abstract

Flor strains of Saccharomyces cerevisiae represent a special group of yeasts used for producing biologically aged wines. We analyzed the collection of commercial wine and flor yeast strains, as well as environmental strains isolated from the surface of grapes growing in vineyards, for resistance to abiotic stresses, adhesive properties, and the ability to form a floating flor. The degree of resistance of commercial strains to ethanol, acetaldehyde, and hydrogen peroxide was generally not higher than that of environmental isolates, some of which had high resistance to the tested stress agents. The relatively low degree of stress resistance of flor strains can be explained both by the peculiarities of their adaptive mechanisms and by differences in the nature of their exposure to various types of stress in the course of biological wine aging and under the experimental conditions we used. The hydrophobicity and adhesive properties of cells were determined by the efficiency of adsorption to polystyrene and the distribution of cells between the aqueous and organic phases. Flor strains were distinguished by a higher degree of hydrophobicity of the cell surface and an increased ability to adhere to polystyrene. A clear correlation between biofilm formation and adhesive properties was also observed for environmental yeast isolates. The overall results of this study indicate that relatively simple tests for cell hydrophobicity can be used for the rapid screening of new candidate flor strains in yeast culture collections and among environmental isolates.

Sherry Wines: Worldwide Production, Chemical Composition and Screening Conception for Flor Yeasts

“…To prevent lactic acid bacteria development, lysozyme could be used, as its muramidase activity has an antibacterial action [39]. Concerning non-Saccharomyces yeasts, these could be Candida stellata, Dekkera anomala, Hanseniaspora guilliermondii, Hanseniaspora uvarum, Issatchenkia terricola, Starmerella bacillaris, Lachancea thermotolerans, and Torulaspora delbrueckii, which are often found in nature on the surface of grapes [40][41][42][43][44]. Further, the wine material is subjected to fortification (encabezado stage, Spanish) by adding ethanol at 15.0-15.5% (v/v ethanol), while the composition of the microflora changes dramatically-ethanolsensitive microorganisms are almost completely replaced by sherry strains of S. cerevisiae, a distinctive feature of which is the ability to form a biofilm on the surface of the wine material-flor 1-3 cm thick [45].…”

“…Further, the wine material is subjected to fortification (encabezado stage, Spanish) by adding ethanol at 15.0-15.5% (v/v ethanol), while the composition of the microflora changes dramatically-ethanolsensitive microorganisms are almost completely replaced by sherry strains of S. cerevisiae, a distinctive feature of which is the ability to form a biofilm on the surface of the wine material-flor 1-3 cm thick [45]. Additionally, an important role in this process is played by such adaptive advantages of Saccharomycetes as high fermentation rate, resistance to alcohol, ability of anaerobic growth and rapid switching of metabolism from enzymatic to oxidative [42,46,47]. This sherry stage takes place in the criadera-solera system in oak barrels with a volume of 500-600 L [5,40].…”

“…In this regard, for an effective search for new candidate strains, a multistage scheme for their screening can be used. At the first stage, genetic screening is carried out [17]; then, the cellular response to short-term exposure to certain toxic agents (ethanol, acetaldehyde, hydrogen peroxide) is studied [95] and the adhesive properties of cells and their ability to form a film are determined [42]. The capacity for sorption on polystyrene and the degree of hydrophobicity of cells according to the nature of their distribution between the aqueous and organic phases can be used as rapid tests for the ability of film formation [91,96,97].…”

“…The capacity for sorption on polystyrene and the degree of hydrophobicity of cells according to the nature of their distribution between the aqueous and organic phases can be used as rapid tests for the ability of film formation [91,96,97]. To select strains with cross-resistance to toxic agents, the following criteria are used: ethanol resistance >63%, peroxide resistance >42%, acetaldehyde resistance >50%, high degree of cell hydrophobicity >60%, and sorption on polystyrene OD 600 > 1.7 [42]. Additionally, for the screening of new sherry strains, an analysis of growth characteristics is carried out (duration of the lag phase and exponential growth, cell doubling time, etc.)…”