title: Impact of mixed Torulaspora delbrueckii-Saccharomyces cerevisiae culture on high-sugar fermentation.
abstract: Conventional wine yeasts produce high concentrations of volatile acidity, mainly acetic acid, during high-sugar fermentation. This alcoholic fermentation by-product is highly detrimental to wine quality and, in some cases, levels may even exceed legal limits. In this study, a non-conventional species, Torulaspora delbrueckii, was used, in pure cultures and mixed with Saccharomyces cerevisiae yeast, to ferment botrytized musts. Fermentation rate, biomass growth, and the formation of volatile acidity, acetaldehyde, and glycerol were considered. This study demonstrated that T. delbrueckii, often described as a low acetic producer under standard conditions, retained this quality even in a high-sugar medium. Unlike S. cerevisiae, this species did not respond to the hyper-osmotic medium by increasing acetic production as soon as it is inoculated into the must. Nevertheless, this yeast produced low ethanol and biomass yields, and the fermentation was sluggish. As a result, T. delbrueckii fermentations do not reach the required ethanol content (14%vol.), although this species can survive at this concentration. A mixed culture of T. delbrueckii and S. cerevisiae was the best combination for improving the analytical profile of sweet wine, particularly volatile acidity and acetaldehyde production. A mixed T. delbrueckii/S. cerevisiae culture at a 20:1 ratio produced 53% less in volatile acidity and 60% less acetaldehyde than a pure culture of S. cerevisiae. Inoculating S. cerevisiae after 5 days' fermentation by T. delbrueckii had less effect on volatile acidity and acetaldehyde production and resulted in stuck fermentation. These results contribute to a better understanding of the behaviour of non-Saccharomyces and their potential application in wine industry.
authors.affiliation: UMR 1219 oenologie, Université Bordeaux 2, INRA, ISVV, 351 cours de Libération, 33400 Talence, France. marina.bely@univ-pau.fr
authors.forename: Marina
authors.initials: M
authors.lastname: Bely
authors.forename: Philippe
authors.initials: P
authors.lastname: Stoeckle
authors.forename: Isabelle
authors.initials: I
authors.lastname: Masneuf-Pomarède
authors.forename: Denis
authors.initials: D
authors.lastname: Dubourdieu
mesh_terms: D000079:Acetaldehyde / Q000032:analysis / Q000378:metabolism; D018533:Biomass; D050260:Carbohydrate Metabolism; D002245:Carbon Dioxide / Q000032:analysis; D018920:Coculture Techniques; D000431:Ethanol / Q000032:analysis / Q000378:metabolism; D005285:Fermentation; D005516:Food Microbiology; D005990:Glycerol / Q000032:analysis / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D009994:Osmolar Concentration; D012441:Saccharomyces cerevisiae / Q000254:growth & development / Q000378:metabolism*; D004718:Saccharomycetales / Q000254:growth & development / Q000378:metabolism*; D013997:Time Factors; D014835:Volatilization; D014920:Wine / Q000382:microbiology*
chemical_list: D002245:Carbon Dioxide; D000431:Ethanol; D000079:Acetaldehyde; D005990:Glycerol