Lucia Oro

Antimicrobial activity of Metschnikowia pulcherrima on wine yeasts

In the present study, it was investigated the antagonistic behaviour of Metschnikowia pulcherrima, as biocontrol agent, against the main wine yeast species involved in the winemaking process.

Non-conventional Yeast Species for Lowering Ethanol Content of Wines.

Rising sugar content in grape must, and the concomitant increase in alcohol levels in wine, are some of the main challenges affecting the winemaking industry nowadays. Among the several alternative solutions currently under study, the use of non-conventional yeasts during fermentation holds good promise for contributing to relieve this problem. Non-Saccharomyces wine yeast species comprise a high number or species, so encompassing a wider physiological diversity than Saccharomyces cerevisiae. Indeed, the current oenological interest of these microorganisms was initially triggered by their potential positive contribution to the sensorial complexity of quality wines, through the production of aroma and other sensory-active compounds. This diversity also involves ethanol yield on sugar, one of the most invariant metabolic traits of S. cerevisiae. This review gathers recent research on non-Saccharomyces yeasts, aiming to produce wines with lower alcohol content than those from pure Saccharomyces starters. Critical aspects discussed include the selection of suitable yeast strains (considering there is a noticeable intra-species diversity for ethanol yield, as shown for other fermentation traits), identification of key environmental parameters influencing ethanol yields (including the use of controlled oxygenation conditions), and managing mixed fermentations, by either the sequential or simultaneous inoculation of S. cerevisiae and non-Saccharomyces starter cultures. The feasibility, at the industrial level, of using non-Saccharomyces yeasts for reducing alcohol levels in wine will require an improved understanding of the metabolism of these alternative yeast species, as well as of the interactions between different yeast starters during the fermentation of grape must.

Fermentative aptitude of non- Saccharomyces wine yeast for reduction in the ethanol content in wine

Abstract Over the last few decades, there has been a progressive increase in the ethanol content in wines due to global climate change and to the new wine styles that are associated with increased grape maturity. This increased ethanol content can have negative consequences on the sensory properties of the wines, human health, and economic aspects. Several microbiological approaches for decreasing the ethanol content have been suggested, such as strategies based on genetically modified yeasts, the adaptive evolution of yeasts, and the use of non-Saccharomyces yeast. In the present study, we investigated the interspecies and intraspecies variability of some non-Saccharomyces wine yeast species under anaerobic fermentation conditions. Across different grape juices and fermentation trials, Hanseniaspora uvarum, Zygosaccharomyces sapae, Zygosaccharomyces bailii, and Zygosaccharomyces bisporus promoted significant reductions in ethanol yield and fermentation efficiency in comparison with Saccharomyces cerevisiae. The diversion of alcoholic fermentation and the abundant formation of secondary compounds might explain the marked reduction in ethanol yield, as determined through the segregation of the majority of the strains according to their species attributes observed using principal component analysis. These data suggest that careful evaluation of interspecies and intraspecies biodiversity can be carried out to select yeast that produces low-ethanol yields.

Starmerella bombicola influences the metabolism of Saccharomyces cerevisiae at pyruvate decarboxylase and alcohol dehydrogenase level during mixed wine fermentation

BackgroundThe use of a multistarter fermentation process with Saccharomyces cerevisiae and non-Saccharomyces wine yeasts has been proposed to simulate natural must fermentation and to confer greater complexity and specificity to wine. In this context, the combined use of S. cerevisiae and immobilized Starmerella bombicola cells (formerly Candida stellata) was assayed to enhance glycerol concentration, reduce ethanol content and to improve the analytical composition of wine. In order to investigate yeast metabolic interaction during controlled mixed fermentation and to evaluate the influence of S. bombicola on S. cerevisiae, the gene expression and enzymatic activity of two key enzymes of the alcoholic fermentation pathway such as pyruvate decarboxylase (Pdc1) and alcohol dehydrogenase (Adh1) were studied.ResultsThe presence of S. bombicola immobilized cells in a mixed fermentation trial confirmed an increase in fermentation rate, a combined consumption of glucose and fructose, an increase in glycerol and a reduction in the production of ethanol as well as a modification in the fermentation of by products. The alcoholic fermentation of S. cerevisiae was also influenced by S. bombicola immobilized cells. Indeed, Pdc1 activity in mixed fermentation was lower than that exhibited in pure culture while Adh1 activity showed an opposite behavior. The expression of both PDC1 and ADH1 genes was highly induced at the initial phase of fermentation. The expression level of PDC1 at the end of fermentation was much higher in pure culture while ADH1 level was similar in both pure and mixed fermentations.ConclusionIn mixed fermentation, S. bombicola immobilized cells greatly affected the fermentation behavior of S. cerevisiae and the analytical composition of wine. The influence of S. bombicola on S. cerevisiae was not limited to a simple additive contribution. Indeed, its presence caused metabolic modifications during S. cerevisiae fermentation causing variation in the gene expression and enzymatic activity of alcohol deydrogenase and pyruvate decarboxilase.

Sequential Fermentation with Selected Immobilized Non-Saccharomyces Yeast for Reduction of Ethanol Content in Wine

The average ethanol content of wine has increased over the last two decades. This increase was due to consumer preference, and also to climate change that resulted in increased grape maturity at harvest. In the present study, to reduce ethanol content in wine, a microbiological approach was investigated, using immobilized selected strains of non-Saccharomyces yeasts namely Starmerella bombicola, Metschnikowia pulcherrima, Hanseniaspora osmophila, and Hanseniaspora uvarum to start fermentation, followed by inoculation of free Saccharomyces cerevisiae cells. The immobilization procedures, determining high reaction rates, led a feasible sequential inoculation management avoiding possible contamination under actual winemaking. Under these conditions, the immobilized cells metabolized almost 50% of the sugar in 3 days, while S. cerevisiae inoculation completed all of fermentation. The S. bombicola and M. pulcherrima initial fermentations showed the best reductions in the final ethanol content (1.6 and 1.4% v/v, respectively). Resulting wines did not have any negative fermentation products with the exception of H. uvarum sequential fermentation that showed significant amount of ethyl acetate. On the other hand, there were increases in desirable compounds such as glycerol and succinic acid for S. bombicola, geraniol for M. pulcherrima and isoamyl acetate and isoamyl alcohol for H. osmophila sequential fermentations. The overall results indicated that a promising ethanol reduction could be obtained using sequential fermentation of immobilized selected non-Saccharomyces strains. In this way, a suitable timing of second inoculation and an enhancement of analytical profile of wine were obtained.

Evaluation of damage induced by Kwkt and Pikt zymocins against Brettanomyces/ Dekkera spoilage yeast, as compared to sulphur dioxide

Over the last few decades, the use of zymocins as biological tools to counteract contamination by spoilage yeast in beverages and food has been widely studied. This study examined the damage induced by the Kwkt and Pikt, two zymocins produced by Kluyeromyces wickerhamii and Wickerhanomyces anomalus, respectively, with antimicrobial activity against Brettanomyces/Dekkera wine‐spoilage yeast.