engleski

Physiological and genetic characterisation of Saccharomyces strains isolated from ice harvest of Chardonnay grapes

Specific ecological environment in the production of wine is ice harvest. Such harvest takes place in extreme temperature conditions while the grapes are still frozen and the microflora of those grapes has specific features like stress tolerance. Yeasts present during fermentation of ice wine have to be adapted to stressful conditions like high sugar content and low pH. In this study wine yeasts present during the Chardonnay ice wine must fermentation were identified and a physiological and genetic characterization of them was performed. In total, twenty-eight yeast strains were isolated during the fermentation and fourteen of them belonged to the Saccharomyces group. Identification at the species level was performed by restriction of the ITS region and six strains of S. cerevisiae as well as eight strains of S. paradoxus were identified. These strains were tested in more detail regarding physiological characteristics, which are important for fermentation of such specific substrate. Most of the isolates (79%) showed significant osmotolerance, which could result from adaptation or genetic inheritance. Flocculation capacity was tested as well but neither strain showed true flocculation in all conditions. A certain degree of flocculation was obtained for two strains, but only when grown in preculture containing calcium ions. SOY 28L showed interesting values and therefore investigation should be continued in the manner of detection and determination of regulation mechanisms leading to that pattern of behavior. The finding indicates that the indigenous isolates could really be competitors of other yeasts in ice wine fermentation and in the future used as a starter culture.

ice wine; fermentation; yeasts

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