Unravelling the microbial community structure and aroma profile of Agiorgitiko wine under different inoculation schemes

Abstract

Agiorgitiko (Vitis vinifera L. cv.) is the most widely cultivated indigenous red grape variety in Greece, known for the production of Protected Designation of Origin Nemea wines. The aim of the present study was to evaluate five different combinations of yeast starters, previously isolated from spontaneous alcoholic fermentation of the same grape variety, for their oenological potential in terms of fermentation predominance and capacity as well as aromatic contribution to Agiorgitiko wine production. Grapes from the Nemea region, crashed and pressed, were inoculated with different yeast species/strains in pure and mixed cultures.  In particular, wines were produced in duplicate with the addition of (A) Saccharomyces cerevisiae SFA1, (B) S. cerevisiae SFA2, (C) S. cerevisiae SFA3, (D) S. cerevisiae SFA3, Hanseniaspora opuntiae SFB1 and (E) S. cerevisiae SFA3, H. opuntiae SFB1, H. opuntiae SFB2 and Hanseniaspora uvarum SFC1. At specific time points during the alcoholic fermentation, amplicon-based metagenomics analysis was employed to unravel the microbial community structure at the genus level. In the end of the fermentation process oenological parameters including volatile acidity, residual sugars and ethanol were determined according to the OIV protocols while the volatile compounds produced were measured by GC/MS. Finally, all produced wines were evaluated  by quantitative descriptive analysis. As expected, Saccharomyces dominated the yeast/fungal microbiota of the A-C wine samples throughout fermentation, followed by Aspergillus, Cladosporium and Aureobasidium, mainly at the early fermentation stage. In D and E wine samples, although Hanseniaspora was the predominant genus in early fermentation, the relative abundance of Saccharomyces rapidly increased and dominated until the end of the fermentation. Compared to yeast/fungi, bacterial community was characterized by a quite higher diversity. Although similar genera were identified in all wine samples (A-E), e.g. Bacillus, Oenococcus, Lactococcus, Staphylococcus and Acinetobacter, their relative abundances varied depending on the sample and fermentation stage. As far as the volatile profile was concerned, the GC/MS analysis revealed that the use of different species/yeasts modified the flavor and aroma of the produced wines. More specifically, exceptional amounts of higher alcohols and medium-chain fatty acid esters (known for their floral and fruity contribution) were observed in the co-inoculated wines (D and E), resulting in a more distinct and intense aromas. According to sensory evaluation the co-inoculation with three different yeast species (wine sample E) significantly increased the aromatic typicity characterized by red fruits aromas. Understating the microbial community structure during the alcoholic fermentation could lead to higher quality wine product and constitute a strong tool to direct wine sensory traits

Acknowledgments

This research has been co-financed by the European Union and Greek national funds through the Operational Program Competitiveness, Entrepreneurship and Innovation, under the call “Greece – Israel Call for Proposals for Joint R&D Projects 2019” (project code: T10ΔΙΣ-00060).