Selected non-Saccharomyces wine yeasts in controlled multistarter fermentations with Saccharomyces cerevisiae
Highlights
► Widespread biodiversity within non-Saccharomyces wine yeasts. ► Mixed fermentation with selected non-Saccharomyces wine yeasts may improve wine quality. ► The modulation of inoculum determines the influence of non-Saccharomyces yeast. ► Interactions in mixed culture fermentations should be further investigated.
Introduction
One of the most important technological advances in winemaking has been the inoculation of grape juice with selected cultures of Saccharomyces cerevisiae. This has been based on the evidence that microbiological control of the fermentation process allows better management of this alcoholic fermentation (Barre and Vezinhet, 1984, Bisson and Kunkee, 1993, Pretorius, 2000, Ranieri and Pretorius, 2000, Fleet, 2008). It is believed that a selected and inoculated strain of S. cerevisiae will suppress any ‘indigenous’ non-Saccharomyces species and dominate the fermentation process. Although this expectation has been widely accepted by winemakers, several studies have revealed that non-Saccharomyces yeasts can indeed persist during the various stages of fermentations that are inoculated with pure cultures of S. cerevisiae (Bouix et al., 1981, Heard and Fleet, 1985, Martinez et al., 1989, Mora et al., 1990).
The use of non-Saccharomyces wine yeasts in pure cultures as fermentation starters has indicated that these have some beneficial and several negative fermentation characteristics. Among the latter, there is the production of acetic acid, ethyl acetate, acetaldehyde and acetoin at high concentrations, which generally prevents the use of such strains as starter cultures. Moreover, most of the non-Saccharomyces species coming from wine-related environments have limited fermentation potential, such as low fermentation power and rates, as well as low SO2 resistance (Herraiz et al., 1990, Ciani, 1997, Ciani and Maccarelli, 1998, Ferreira et al., 2001, Farkas et al., 2005, Garde-Cerdán and Ancín-Azpilicueta, 2006, Howell et al., 2006, Jolly et al., 2006). However, over the last decade, several studies have been revaluating the involvement of non-Saccharomyces yeasts during alcoholic fermentation and their role on the metabolic impact and aroma complexity of the final product (Lema et al., 1996, Egli et al., 1998, Henick-Kling et al., 1998, Rojas et al., 2001, Zohre and Erten, 2002, Fleet, 2003, Jolly et al., 2003, Domizio et al., 2007).
In mixed fermentations, such as natural fermentations, some negative enological characters of non-Saccharomyces yeasts might not be expressed, or might be modified by S. cerevisiae cultures (Howell et al., 2006, Anfang et al., 2009, Varela et al., 2009). Different studies have shown that in natural fermentations, Saccharomyces and non-Saccharomyces yeasts do not passively coexist; instead, they appear to interact. Under these conditions, some enological traits of the non-Saccharomyces yeasts are not expressed, or they can be modulated by the S. cerevisiae yeast cultures (Ciani and Ferraro, 1998, Ciani et al., 2006, Bely et al., 2008, Anfang et al., 2009). In this context, the use of controlled mixed fermentations of Saccharomyces and non-Saccharomyces yeast species isolated from the wine environment has been proposed (Soden et al., 2000, Toro and Vazquez, 2002, Ciani et al., 2006, Ciani et al., 2010, Jolly et al., 2006, Mendoza et al., 2007, Moreira et al., 2008, Anfang et al., 2009). Indeed, the use of non-Saccharomyces wine yeasts together with Saccharomyces strains in mixed fermentations might be recommended as a tool to obtain the advantages of spontaneous fermentation, while avoiding the risks of stuck fermentation (Romano et al., 2003, Rojas et al., 2003, Jolly et al., 2006, Ciani et al., 2010). Furthermore, non-Saccharomyces wine yeasts have some specific enological characteristics that are absent in S. cerevisiae species, and these can have additive effects on wine flavour and aroma (Languet et al., 2005, Strauss et al., 2001, Viana et al., 2008).
In the present study, we initially characterized 34 non-Saccharomyces yeasts isolated from wine-related environments, with the aim of determining their enological potential. On the basis of this characterization, four of these non-Saccharomyces yeasts were selected to be used together with starter cultures of S. cerevisiae. The fermentation behavior of these mixed cultures and the analytical profiles of the final wines were then evaluated. Here, we show that in winemaking, the use of controlled mixed cultures of selected non-Saccharomyces and Saccharomyces strains can have advantages over fermentations inoculated with pure cultures of S. cerevisiae. This can thus lead to the production of wines with more predictable and desirable characteristics.
Section snippets
Microorganisms and media
Thirty-four non-Saccharomyces strains from the Yeast Culture Collection of the SAIFET Department of the Polytechnic University of Marche (Ancona, Italy) and belonging to the genera Candida, Torulaspora, Lachancea (formerly known as Kluyveromyces) and Metschnikowia were used. All of the strains had been previously identified by PCR-RFLP analysis of their rDNA internal transcribed spacers (Stringini et al., 2009). The Lalvin EC1118 S. cerevisiae commercial strain (purchased as active dry yeast by
Selection of non-Saccharomyces yeasts
The initial screening of 34 non-Saccharomyces yeasts belonging to the genera Candida, Torulaspora, Lachancea and Metschnikowia was carried out according to the main enological characters and enzymatic activities. The data from this screening on agar plate are shown in Table 1. The comparison between S. cerevisiae control strains, that showed full SO2 resistance (level 4), and the non-Saccharomyces strains studied showed marked differences. In particular, yeasts belonging to the genera Candida
Discussion
Over the last few years, several studies have re evaluated the use of non-Saccharomyces yeasts in controlled mixed fermentations (Ciani et al., 2010), indicating that rational selection of non-Saccharomyces yeasts can lead to the obtainment of selected cultures that can be used in association with S. cerevisiae for must fermentation (Romano et al., 1992, Ciani and Maccarelli, 1998, Viana et al., 2008, De Benedictis et al., 2010).
In the present study, 34 non-Saccharomyces strains that belong to
Acknowledgements
The present work is part of a research project coordinated and financed by Consorzio Tuscania (http://www.consorziotuscania.it), Firenze, Italy.
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