Wine strains of S. cerevisiae

One of the major areas of research interest in wine strains of S. cerevisiae is the analysis of response to stress. This focus is motivated by both practical and fimdamental interests. The production of wine imposes both biotic and abiotic stresses on the yeast. The principal stresses encountered are high osmolarity, high ethanol, extremes of temperature, nutrient limitation, and presence of inhibitory metabolites (Bisson, 1999). Genomic analysis of the response to each of these types of stress has been conducted (Alexandre et al., 2001 Aranda and del Olmo, 2004 Backhus et al., 2001 Erasmus et al., 2003 Kuhn et al., 2001 Marks et al., 2003 Rep et al., 2000 Rossignol et al., 2006 Sahara et al., 2002). Several... 

This is what occurred to those strains of S. cerevisiae selected for traditional vinification processes (whether a commercial starter and not) that have been tested for the production of sweet wines, such as Picolit (Urso et al., 2008) and Vin Santo wine (Domizio et al., 2008) here, they were not able to dominate the relative fermentation process. On the contrary, Unican Sherry yeast, which is normally used for the production... 

Accordingly, Muratore et al. (2007) used a S. uvarum strain for the fermentation of Malvasia delle Lipari, a grape variety that is also used for the production of sweet wine, and they investigated further the chemical and sensory properties of the relevant wines, comparing the results with those obtained with a commercial strain of S. cerevisiae. Lower volatile acidity, lower alcohol content, and higher total acidity were reported for the wine produced by S. uvarum, with higher scores for positive attributes assigned by a panel for the wine fermented with S. uvarum. 

In a more recent study, Lencioni et al. (2009) reported the chemical composition and perceivable characteristics of wine obtained under ambient conditions (vinsantaia) with and without addition of madre and using different strains of S. cerevisiae. It was found that the different S. cerevisiae strains showed different fermentation behaviors and produced wines with different compositional and organoleptic characteristics. In particular, by the fermentations conducted with madre addition it was reached... 

Similar techniques were used by Shinohara et al (71) to develop hybrids with increased production of fusel alcohols and esters. Protoplast fusion techniques have been used to confer amylolytic activity to brewery yeasts (22) and ethanol tolerance to wine yeasts (70) Farris et al (72) used protoplast fusion to produce hybrids with killer factor that is, the ability to secrete proteinic toxins. Kunkee and coworkers (25) utilized a leucine auxotrophic mutant strain of S. cerevisiae (UCD Montrachet 522) to produce base wine for brandy production the mutant strain produces less isoamyl alcohol, reducing the quantity of fusel alcohols in the subsequent brandy. And Thornton (48) discussed the progress in utilizing plasmid vectors to introduce new genes into wine yeasts he cautioned, however, that until the yeast genome is better understood that direct gene manipulation techniques will be of limited value. 

In this study, commercial Fino sherry wines (5 years of biological ageing) which were selected by expert tasters as more representative were used. Also, selected strains of S. cerevisiae and S, bayamis (Kurtzman Fell, 1998) were used. These yeast strains, corresponding to the S. cerevisiae capensis and bayanus races in the Kreger-van Rij classification (1984), were isolated from a velum of industrial wine produced in the Montilla-Moriles region. The criteria and tests for their selection have been reported in previous papers (Guijo et al., 1986 Moreno et al., 1991). 

Wine research and wine yeast strain development are certainly well placed to benefit from the privileged place that S. cerevisiae occupies in the life sciences. Figure 9.14 summarises several targets of strain development programmes. These targets are normally, but not exclusively, focussed on the natural metabolites that various strains of S. cerevisiae produce under different fermentation conditions (Figure 9.15). The following includes some examples that demonstrate this. 

The Kl toxin is a small protein made up of two sub-units (9 and 9.5 kDa). It is active and stable in a very narrow pH range (4.2-4.6) and is therefore inactive in grape must. The K2 toxin, a 16 kDa glycoprotein, produced by homothallic strains of S. cerevisiae encountered in wine, is active at between pH 2.8 and 4.8 with a maximum activity between 4.2 and 4.4. It is therefore active at the pH of grape must and wine. 

Why do some S. cerevisiae strains issued from a very heterogeneous population become dominant during spontaneous fermentation Why can they be found several years in a row at the same vineyard and wine cellar Despite their practical interest, these questions have not often been studied and there are no definitive responses. It seems that these strains rapidly start and complete alcoholic fermentation and have a good resistance to sulfur dioxide (up to 10 g/hl). Furthermore, during mixed inoculations in the laboratory of either 8% ethanol or non-fermented musts, these strains rapidly become dominant when placed in the presence of other wild non-dominant strains of S. cerevisiae isolated at the start and end of fermentation. This subject merits further research. Without a doubt, it would be interesting to compare the genetic characteristics of dontinant and non-dominant... 

Mutation. For industrial appHcations, mutations are induced by x-rays, uv irradiation or chemicals (iiitrosoguanidine, EMS, MMS, etc). Mutant selections based on amino acid or nucleotide base analogue resistance or treatment with Nystatin or 2-deoxyglucose to select auxotrophs or temperature-sensitive mutations are easily carried out. Examples of useful mutants are strains of Candida membranefaciens, which produce L-threonine Hansenu/a anomala, which produces tryptophan or strains of Candida lipolytica that produce citric acid. An auxotrophic mutant of S. cerevisiae that requires leucine for growth has been produced for use in wine fermentations (see also Wine). This yeast produces only minimal quantities of isoamyl alcohol, a fusel oil fraction derived from leucine by the Ehrlich reaction (10,11). A mutant strain of bakers yeast with cold-sensitive metaboHsm shows increased stabiUty and has been marketed in Japan for use in doughs stored in the refrigerator (12). 

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