Abstract
Some non-Saccharomyces yeasts, including Metschnikowia pulcherrima, have been proposed as selected starters due to their contribution for the overall aroma and chemical profiles of wines. In this work, we aimed to evaluate the genetic and phenotypic diversity of Metschnikowia pulcherrima strains isolated from different locations of Douro Wine Region, and to explore their potential as co-adjuncts of S. cerevisiae in alcoholic fermentation. For that purpose, a set of 64 M. pulcherrima isolates were used. Polymerase chain reaction (PCR) fingerprinting with M13 primers demonstrated to be an efficient tool in intraspecific discrimination of M. pulcherrima strains. No significant associations were found between genotypic profiles and either geographical origin or winery. The isolates were screened for their stress resistance ability (ethanol, SO2, chitosan, copper, H2O2, and Grape Juice Medium), aroma-related activities (resistance to 5, 5′, 5′′-trifluor-d, l-leucine and cerulenin and β-glycosidase, β-lyase and sulfite-reductase activities) as well as other relevant technological proprieties (protease activity and biogenic amines production). M. pulcherrima response to the different enological traits evaluated was greatly strain-dependent. The most discriminant features were the ability of the strains to grow in Grape-Juice Medium (GJM) and sulfite-reductase, and their β-lyase and protease activities. The enological potential of a selected M. pulcherrima strain in mixed-culture with S. cerevisiae was also assessed in natural grape-juice of a local variety, under two nitrogen regimes. M. pulcherrima proved to be promising for future industrial application as a co-starter, lowering ethanol, acetic acid and, reported here for the first time, lowering hydrogen sulfide levels in the wines.
Highlights
Winemaking is a natural process conducted by yeast present on grape-musts.Yeast genera frequently found on grapes and in must include Hanseniaspora, Candida, Metschnikowia, Kluyveromyces, Schizosaccharomyces, Torulaspora, Rhodotorula, Zygosaccharomyces, and Cryptococcus [1].These non-Saccharomyces yeasts initiate spontaneous alcoholic fermentation of the juice, but they are rapidly surpassed by the growth of Saccharomyces cerevisiae as a consequence of their weak SO2 and ethanol tolerance [1,2,3,4]
This set included, 64 Metschnikowia pulcherrima strains isolated from the three main sub-regions of the Douro Wine Region, Baixo Corgo, Cima Corgo and Douro Superior (Figure 1) and the type strain obtained from the Spanish Type Culture Collection (CECT 11202)
To our knowledge this is the first work reporting the biodiversity of Metschnikowia pulcherrima strains taking inconsideration relevant enzymatic activities and their ability to grow and persist during alcoholic fermentation
Summary
Yeast genera frequently found on grapes and in must include Hanseniaspora, Candida, Metschnikowia, Kluyveromyces, Schizosaccharomyces, Torulaspora, Rhodotorula, Zygosaccharomyces, and Cryptococcus [1]. These non-Saccharomyces yeasts initiate spontaneous alcoholic fermentation of the juice, but they are rapidly surpassed by the growth of Saccharomyces cerevisiae as a consequence of their weak SO2 and ethanol tolerance [1,2,3,4]. Fermentation 2018, 4, 8 undesirable compounds [1,4] such as the biogenic amines [5] These so-called “natural fermentations” results in inconsistent wines from vintage to vintage.
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