Autochthonous yeasts and Oenococcus oeni strains: different inoculation time and wine safety and quality

The study of interactions among different microbial populations that take place in wine microbial communities is interesting for the understanding of their impact on wines' quality. The main interactions occur among yeast Saccharomyces cerevisiae, yeast non-Saccharomyces spp. and lactic acid bacteria. In last years, there is a special interest in the study of non-Saccharomyces yeasts as they are responsible for a substantial part of the aromatic complexity. Hanseniaspora uvarum has been proved to positively modify the wine chemical composition, especially contribute to the sensory characteristics of wines. In the light of the rising request for autochthonous starters tailored for given 'terroir', the objective of this work was to select the best inoculation time of 5 autochthonous of Oenococcus oeni strains in combination with 2 S. cerevisiae and one H. uvarum strains isolated from Apulian wines. Microvinifications were performed using must from Apulian grape varieties. Both, yeasts S. cerevisiae and H. uvarum, were co-inoculated and O. oeni strains were co-inoculated or sequentially inoculated during alcoholic fermentation, when ethanol content was 2%, 4%, 6%, 8%, 10% or 12% (v/v). Ethanol formation, malic acid consumption and cell viability were monitored during the vinifications. Results showed that ethanol level at the moment of bacterial inoculation was crucial for developing malolactic fermentation. The co-inoculation with S. cerevisiae and H. uvarum was the best strategy for maintaining highest O. oeni populations and therefore for carrying out MLF in red must. Significant differences in L-malic consumption were found depending on the O. oeni strain inoculated. Among the O. oeni strains, OT4 presented the highest malolactic activity, consuming completely the malic acid in all the ethanol concentrations studied. In the case of O. oeni OT4, we studied the expression of selected genes to better understand the interaction of this strain with the yeast biotypes used in this study This research was supported by the Apulian Region Project cod. QCBRAJ6 "Biotecnologie degli alimenti per l'innovazione e la competitività delle principali filiere regionali: estensione della conservabilità e aspetti funzionali - BIOTECA."