Fungal Diversity Analysis of Grape Musts from Central Valley-Chile and Characterization of Potential New Starter Cultures.

Dinka Mandakovic,Jonathan Maldonado,Wladimir Mardones,Mauricio González,Rodrigo Pulgar,Francisco A Cubillos,Verónica Cambiazo

doi:10.3390/microorganisms8060956

Abstract

Autochthonous microorganisms are an important source of the distinctive metabolites that influence the chemical profile of wine. However, little is known about the diversity of fungal communities associated with grape musts, even though they are the source of local yeast strains with potential capacities to become starters during fermentation. By using internal transcribed spacer (ITS) amplicon sequencing, we identified the taxonomic structure of the yeast community in unfermented and fermented musts of a typical Vitis vinifera L. var. Sauvignon blanc from the Central Valley of Chile throughout two consecutive seasons of production. Unsurprisingly, Saccharomyces represented the most abundant fungal genus in unfermented and fermented musts, mainly due to the contribution of S. uvarum (42.7%) and S. cerevisiae (80%). Unfermented musts were highly variable between seasons and showed higher values of fungal diversity than fermented musts. Since microbial physiological characterization is primarily achieved in culture, we isolated nine species belonging to six genera of fungi from the unfermented must samples. All isolates were characterized for their potential capacities to be used as new starters in wine. Remarkably, only Metschnikowia pulcherrima could co-exist with a commercial Saccharomyces cerevisiae strain under fermentative conditions, representing a feasible candidate strain for wine production.

Highlights

During alcoholic fermentation of grape musts, sugars are transformed into ethanol and carbon dioxide by the actions of fermentative yeasts, mainly Saccharomyces cerevisiae
Saccharomyces strains showed the highest ethanol and synthetic wine must MS300 (SWM) μmax, clustering together for all estimated parameters (Supplementary Figure S2). These results demonstrate the dominance of Saccharomyces strains across wine-related phenotypes; it highlights that other non-conventional yeasts are able to tolerate high sugar and/or ethanol levels
Taking into account that the diversity of yeasts during grape must fermentation [21] or associated with grape berries in different Chilean valleys [20] have been described using mainly cultivation techniques and/or qPCR-based assays, here we performed a high-throughput sequencing (HTS) approach based on the internal transcribed spacer (ITS)-sequencing of all the eukaryotic microorganisms present in the unfermented and fermented musts in consecutive seasons

Summary

Introduction

During alcoholic fermentation of grape musts, sugars are transformed into ethanol and carbon dioxide by the actions of fermentative yeasts, mainly Saccharomyces cerevisiae. S. cerevisiae is the primary microorganism responsible to complete wine fermentation, at present, a re-evaluation of the role of non-conventional yeasts in winemaking and their use as selected starters in mixed fermentations with S. cerevisiae is being carried out [5]. In this context, non-conventional yeasts have the potential to positively contribute to the wine sensory profile through their distinctive production of secondary metabolites and fine-tune the ethanol and glycerol concentrations in wine [5,6]

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