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As a consequence of alcoholic fermentation (AF) in wine, several compounds are released by yeasts, and some of them are linked to the general quality and mouthfeel perceptions in wine. However, others, such as succinic acid, act as inhibitors, mainly of malolactic fermentation. Succinic acid is produced by non-Saccharomyces and Saccharomyces yeasts during the initial stages of AF, and the presence of some amino acids such as γ-aminobutyric acid (GABA) and glutamic acid can increase the concentration of succinic acid. However, the influence of these amino acids on succinic acid production has been studied very little to date. In this work, we studied the production of succinic acid by different strains of non-Saccharomyces and Saccharomyces yeasts during AF in synthetic must, and the influence of the addition of GABA or glutamic acid or a combination of both. The results showed that succinic acid can be produced by non-Saccharomyces yeasts with values in the range of 0.2-0.4 g/L. Moreover, the addition of GABA or glutamic acid can increase the concentration of succinic acid produced by some strains to almost 100 mg/L more than the control, while other strains produce less. Consequently, higher succinic acid production by non-Saccharomyces yeast in coinoculated fermentations with S. cerevisiae strains could represent a risk of inhibiting Oenococcus oeni and therefore the MLF., (© 2023. The Author(s).)

Saccharomyces cerevisiae is a highly fermentative species able to complete the wine fermentation. However, the interaction with other non-Saccharomyces yeasts can determine the fermentation performance of S. cerevisiae. We have characterised three rare non-Saccharomyces yeasts (Cyberlindnera fabianii, Kazachstania unispora and Naganishia globosa), studying their impact on S. cerevisiae fitness and wine fermentation performance. Using a wide meta-taxonomic dataset of wine samples, analysed through ITS amplicon sequencing, we show that about a 65.07% of wine samples contains Naganishia spp., a 27.21% contains Kazachstania spp., and only a 4.41% contains Cyberlindnera spp; in all cases with average relative abundances lower than 1% of total fungal populations. Although the studied N. globosa strain showed a limited growth capacity in wine, both K. unispora and C. fabianii showed a similar growth phenotype to that of S. cerevisiae in different fermentation conditions, highlighting the outstanding growth rate values of K. unispora. In mixed fermentations with S. cerevisiae, the three yeast species affected co-culture growth parameters and wine chemical profile (volatile compounds, polysaccharides and proteins). K. unispora DN201 strain presents an outstanding capacity to compete with S. cerevisiae strains during the first stage of wine fermentation, causing stuck fermentations in both synthetic and natural grape musts., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Non-Saccharomyces yeasts have increasingly been used in vinification recently. This is particularly true of Torulaspora delbrueckii and Metschnikowia pulcherrima, which are inoculated before S. cerevisiae, to complete a sequential alcoholic fermentation. This paper aims to study the effects of these two non-Saccharomyces yeasts on malolactic fermentation (MLF) carried out by two strains of Oenococcus oeni, under cellar conditions. Oenological parameters, and volatile and phenolic compounds were analysed in wines. The wines were tasted, and the microorganisms identified. In general, non-Saccharomyces created more MLF friendly conditions, largely because of lower concentrations of SO 2 and medium chain fatty acids. The most favourable results were observed in wines inoculated with T. delbrueckii, that seemed to promote the development of O. oeni and improve MLF performance., (Copyright © 2020 Elsevier B.V. All rights reserved.)