Abstract
The present study analyzes the lack of culturability of different non-Saccharomyces strains due to interaction with Saccharomyces cerevisiae during alcoholic fermentation. Interaction was followed in mixed fermentations with 1:1 inoculation of S. cerevisiae and ten non-Saccharomyces strains. Starmerella bacillaris, and Torulaspora delbrueckii indicated longer coexistence in mixed fermentations compared with Hanseniaspora uvarum and Metschnikowia pulcherrima. Strain differences in culturability and nutrient consumption (glucose, alanine, ammonium, arginine, or glutamine) were found within each species in mixed fermentation with S. cerevisiae. The interaction was further analyzed using cell-free supernatant from S. cerevisiae and synthetic media mimicking both single fermentations with S. cerevisiae and using mixed fermentations with the corresponding non-Saccharomyces species. Cell-free S. cerevisiae supernatants induced faster culturability loss than synthetic media corresponding to the same fermentation stage. This demonstrated that some metabolites produced by S. cerevisiae played the main role in the decreased culturability of the other non-Saccharomyces yeasts. However, changes in the concentrations of main metabolites had also an effect. Culturability differences were observed among species and strains in culture assays and thus showed distinct tolerance to S. cerevisiae metabolites and fermentation environment. Viability kit and recovery analyses on non-culturable cells verified the existence of viable but not-culturable status. These findings are discussed in the context of interaction between non-Saccharomyces and S. cerevisiae.
Highlights
Spontaneous wine fermentation is driven by a succession of different yeast species
We investigated the interaction between S. cerevisiae NSa and 10 non-Saccharomyces strains from different sources belonging to H. uvarum, S. bacillaris, M. pulcherrima, and T. delbrueckii to analyze the interactions in mixed fermentation between S. cerevisiae and each individual strain
The culturability loss of non-Saccharomyces strains during late stages of alcoholic fermentation has been well documented (Fleet, 2003)
Summary
A great variety of non-Saccharomyces yeast species originate from grape berries and survive during the early stages of fermentation, such as species from the genera Candida, Hanseniaspora, Lachancea, Metschnikowia, Pichia, and Torulaspora (Fleet, 2003). Some species such as Starmerella bacillaris and Hanseniaspora uvarum grow to a high density (105–107 cells/mL) and dominate other non-Saccharomyces species. As more non-conventional wine yeasts have been explored as wine starters in mixed fermentation with S. cerevisiae (Masneuf-Pomarede et al, 2016), studies on culturability loss of different non-Saccharomyces strains will help in understanding their final impact on wine quality
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