Abstract
SUMMARYStarmerella bacillaris (synonym Candida zemplinina) is an important non-Saccharomyces yeast in winemaking with valuable oenological properties, accompanying Saccharomyces species in sweet wine fermentation, and has been suggested also for application as combined starter culture in dry or sweet wines. In this study, the major metabolites and nitrogen utilization of these yeasts are evaluated in the musts with high or extremely high sugar concentration. The change in the metabolic footprint of Saccharomyces cerevisiae, Saccharomyces uvarum and Starmerella bacillaris strains was compared when they were present as pure cultures in chemically defined grape juice medium with 220 and 320 g/L of sugar, to represent a fully matured and an overripe grape. Surprisingly, the extreme sugar concentration did not result in a considerable change in the rate of sugar consumption; only a shift of the sugar consumption curves could be noticed for all species, especially for Starmerella bacillaris. At the extreme sugar concentration, Starmerella bacillaris showed excellent glycerol production, moderate nitrogen demand together with a noticeable proline utilisation. The change in the overall metabolite pattern of Starmerella bacillaris allowed clear discrimination from the change of the Saccharomyces species. In this experiment, the adequacy of this non-Saccharomyces yeast for co-fermentation in juices with high sugar concentration is highlighted. Moreover, the results suggest that Starmerella bacillaris has a more active adaptation mechanism to extremely high sugar concentration.
Highlights
Fermentation of natural sweet wines has always been a big challenge in winemaking, but the global changes in the climate influence the parameters of the raw grape juice, and as a consequence the quality of the dry or semi-sweet wines
Strains of three yeast species used in this study are as follows: three Starmerella bacillaris strains: Y1667 (CBS9494 type strain) and Y1756 from the National Collection of Agricultural and Industrial Microorganisms (NCAIM), Budapest, Hungary, isolated from botrytized Tokaj grape, and strain MLO from the Department of Oenology, Szent István University (DOSZIU) culture collection, Budapest, Hungary, isolated from wine, six Saccharomyces cerevisiae strains: UVAFERMPM and UVAFERM228 commercial wine yeasts, strains SC57, RA100 and SB12 from DO-SZIU, isolated from Tokaj Aszú wine, and strain S701 from DO-SZIU, isolated from the wine from Somló wine region, and three Saccharomyces uvarum strains: CBS395, type strain from NCAIM, SB42 from DO-SZIU, both isolated from Tokaj Aszú wine, and S103 from DO-SZIU, isolated from the wine from Somló wine region
The most striking observation is that the extreme sugar concentration (320 g/L) did not influence significantly the rate of sugar consumption by S. uvarum, and in particular by S. bacillaris strains
Summary
Fermentation of natural sweet wines has always been a big challenge in winemaking, but the global changes in the climate influence the parameters of the raw grape juice, and as a consequence the quality of the dry or semi-sweet wines. The higher initial sugar concentration is one of the most important factors involved, which could be a considerable challenge for the yeasts. In making some special sweet wines like botrytized or straw wines, sugar content of the grapes may reach an extremely high level, multiplying these effects. Using starter cultures for wine fermentation originally meant exclusively single-strain (Saccharomyces cerevisiae or occasionally Saccharomyces uvarum) products. The industrial exploitation of selected non-Saccharomyces yeasts in combination with Saccharomyces strains as oligo-starter cultures has become an emerging trend [35].
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