Fermentative volatilome modulation of Muscat Ottonel wines by using yeast starter cultures
Graphical abstract
Introduction
The wine aroma is a property that consumers highly value when choosing a product. Currently, an important percentage of wine consumers prefers high aromatic young wines with soft and fresh fruity odors. Therefore, it is of great importance for winemakers that the aroma of their wines can be characterized by objective methods with a scientific basis to improve the processes and the quality of final products. It is known that the content in volatile compounds of young wines is a result of the grape metabolism and the conversion of sugars, amino acids, sulfur compounds and other grape components by yeasts through its secondary metabolism (Mansurova, Ebert, Blank, & Ibañez, 2017). Consequently, the use of different aromatic grape varieties and suitable fermentative yeast strains lead to wines with significant aroma differences. Nevertheless, only few grape varieties have been studied while other widely cultivated varieties in some European countries with great potential to elaborate high quality wines remain unknown. This is the case of Muscat Ottonel (MO), an aromatic and relatively young grape cultivar, resistant to cold climates and little-distinguished member of the Muscat family. This variety is cultivated in Romania, Austria and Alsace. Some aspects of MO grapes concerning their contents in mono-terpenes and aroma precursors have been studied by Luan, Hampel, Mosandl, and Wust (2004) and Vararu, Moreno-Garcia, Cotea, and Moreno (2015). Furthermore, the maceration (Stoica, Muntean, Baduca, & Mitroi, 2015) and finning treatments effects on the contents of these compounds in wines were studied (Cabaroglu, Razungles, Baumes, & Gunata, 2003). Nevertheless, there is scarce and shortcoming literature about the effect of yeasts on MO wine volatiles (Vas, Blechschmidt, Kovacs, & Vekey, 1999; Vas, Koteleky, Farkas, Dobo, & Vekey, 1998).
Industrially, there are two models to conduct fermentations: i) spontaneous, allowing the growth of indigenous grape microbiota and ii) direct inoculum, using yeast starter cultures aimed to reach a high cell population in the fermenting must. The spontaneous fermentation is an old winemaking procedure that, in best conditions, contributes to the enhancement of typicity and sensorial complexity of the obtained wines. The main drawbacks are the uncontrolled variability in the wine quality, a low reproducibility year to year, a higher risk of sluggish and stuck fermentations and consequently, production of low-quality wines (Ciani et al., 2016). However, the use of starter cultures of selected yeast strains has become a common practice among winemakers. These fermentations diminish the negative effects of the uncontrolled microbiota allowing better control of alcoholic fermentation and therefore obtaining wines with most reproducible sensorial properties and enological characteristics. Some disadvantages reported, like the homogeneity in sensory properties of wines elaborated (Hranilovic et al., 2018; Padilla, Gil, & Manzanares, 2016), can be overcome by using different yeast strains.
Recent publications (Ebert, Halbfeld, & Blank, 2017; Mansurova et al., 2017) introduce the “volatilome” concept to describe the effect of Saccharomyces spp. on the content of volatile metabolites. This concept includes the most important factors influencing the wine aroma and provides a very objective evaluation criterion.
The identification and quantification of volatile compounds require the use of extraction/concentration procedures before their separation/detection by Gas Chromatography-Mass Spectrometry (GC-MS) techniques. The static or dynamic headspace (HS or DHS), purge and trap (P&T), solid-phase micro extraction (SPME), supercritical fluids extraction (SFE) or microwave-assisted extraction (MAE) are some techniques used for this purpose. Nevertheless, Stir-Bar-Sorptive Extraction (SBSE) technique, followed by a thermal desorption (TD) and GC-MS, is revealed as the most successfully analytical platform applied to the evaluation of grape and wine volatiles (Tredoux et al., 2008; Malherbe, Watts, Nieuwoudt, Bauer & du Toit, 2009; Pedroza, Zalacain, Lara, & Salinas, 2010; Arbulu et al., 2013; Vararu et al., 2015; Hirst & Richter, 2016; Martinez-Garcia, Garcia-Martinez, Puig-Pujol, Mauricio, & Moreno, 2017).
This study focus on the volatilome of Muscat Ottonel wines obtained by fermenting the same must with different yeast starter cultures and aims to establish objective criteria for the yeast selection, contributing to the innovation in wine industries and helping to the winemakers in the elaboration of new wine types according to consumer preferences.
Section snippets
Winemaking conditions and yeasts tested
Healthy grapes of Muscat Ottonel variety, from Iasi (Romania), were harvested at the industrial ripe stage, characterized by a sugar content of 226 ± 1 g/L, pH 4.1 ± 0.1 and total acidity of 6.7 ± 0.1 g/L (expressed as tartaric acid). Grapes were destemmed, crushed and pressed and the obtained must was supplied with 100 mg/L of potassium metabisulfite, homogenized and transferred to 27 glass vessels with 25 L capacity. Each vessel was filled with 17 L constituting nine lots of three vessels
General wine characteristic
Wines obtained by spontaneous fermentation (M0) showed the lowest ethanol yields as well as higher values in volatile acidity and concentration of non-fermented sugars compared to the remaining wines (Table 1). The higher glycerol content was registered in M5 followed by M4 and M0, while M1 exhibited the lowest content in this compound. Regarding the volatile acidity, wines from M7 and M8 yeasts displayed the lowest values compared to the remaining starter cultures tested revealing a different
Conclusions
Eight fermentations of Muscat Ottonel grapes were conducted by using eight different Saccharomyces cerevisiae yeast as starter cultures and one by the indigenous grape microbiota as a control. Ten key volatile metabolites were selected among the thirty-seven quantified, allowing to differentiate six wine groups, depending on strain used. However, six odorant series, which groups the Odor Activity Values of all volatiles, established only four wine groups and the organoleptic evaluation of the
Ethical approval
This article does not contain any studies with human participants performed by any of the authors.
CRediT authorship contribution statement
Florin Vararu: Formal analysis, Writing - original draft. Jaime Moreno-García: Formal analysis, Writing - original draft. Marius Niculaua: Resources. Valeriu V. Cotea: Conceptualization, Funding acquisition, Visualization. Manuel Mayén: Methodology, Writing - review & editing. Juan Moreno: Conceptualization, Writing - review & editing.
Declaration of competing interest
Compliance with ethical standards: Authors have no competing interest.
Acknowledgements
To Minami Ogawa, PhD student, for her assistance with English language editing.
Co-Funded by: University of Córdoba (Spain). Ref. XXIII PP Mod. 4.2 Synergies. European Social Fund, Human Resources Development Operational Program. Project POSDRU/159/1.5/S/132765.
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