Elsevier

Analytica Chimica Acta

Volume 660, Issues 1–2, 15 February 2010, Pages 68-75
Analytica Chimica Acta

Volatile and sensory profile of organic red wines produced by different selected autochthonous and commercial Saccharomyces cerevisiae strains

https://doi.org/10.1016/j.aca.2009.09.040Get rights and content

Abstract

Organic wines were produced at pilot scale to select the best autochthonous and commercial yeast strains to obtain wines with high organoleptic qualities. We tested the behaviour of five S. cerevisiae yeast strains and determined their volatile composition and organoleptic characteristics by sensory analysis. A total of 51 volatile compounds were quantified in the wines produced. The concentration of most of the volatile compounds was significantly influenced depending on which yeast strain was inoculated. The differences observed in the volatile composition of the wines appear to be quantitative rather than qualitative. In general, acetals were the most abundant group of volatile compounds in all the samples studied, followed by alcohols without ethanol. The highest contents of volatile compounds were found in two of the wines produced by autochthonous yeast strains. The results obtained in the sensory analysis suggest that autochthonous yeast produced wines of higher organoleptic quality because this sample gave the highest value for the general impression attribute.

Introduction

Growing concern among consumers in developed countries regarding the health and the protection of the environment has increased the demand for organic food over the last decade (especially in Germany, the United Kingdom, Switzerland, New Zealand, Japan, and the United States). Among organic products, EU consumers have shown an increasing interest in organic wines. More and more new organically based wineries are being established and old traditional wineries are adding organic wine to their product lines [1].

Wine quality is influenced, in part, by the composition of the grape juice and by the microbial communities present during the fermentation process. Aroma is one of the main characteristics that determine a wine's quality and value. The aroma of wine is a unique mixture of volatile compounds originating from grapes (varietal aromas), secondary products formed during the wine fermentation (fermentative aromas) and aging (post-fermentative aromas) [2]. The volatile fraction of wine can be made up of more than 800 different compounds [3] with a wide concentration range varying from hundreds of mg L−1 to μg L−1 or ng L−1 levels [4]. This great variety of volatile compounds, with different polarities, volatilities and a wide range of concentrations, is responsible for the complexity of the wine's bouquet and ensures its specificity and character [5].

The particular importance of each compound to the final aroma is related to its odour perception threshold [4]. General approaches to identifying “important” or high impact odorants are based on odour activity values (OAVs) and the concentration/threshold ratio. Odorants with low OAVs, or low impact odorants (i.e. with typical values <1) are generally considered to be unimportant to the overall sensory perception [6].

However, Ryan et al. [6] hypothesise that compounds with low OAVs could play a critical role in characterizing the overall odour of a sample. Furthermore, other authors think that OAVs provide only a rough evaluation of the real contribution of each compound to the overall aroma. In fact, the volatility and the perception of aroma compounds are significantly affected by the basic chemical composition of the wine, which can both mask the odour impact of certain compounds present in concentrations above their detection thresholds and favour the detection of other molecules present in concentrations below theirs [7].

A vast number of volatile compounds are formed and modulated by yeast during alcoholic fermentation and significantly impact the flavour and overall quality of wines [8]. The volatile compounds synthesized by wine yeast include higher alcohols, medium- and long-chain volatile acids, acetate esters, ethyl esters and aldehydes among others [9], [10]. The capacity to form aroma depends not only on yeast species but also on the particular strain of the individual species [11]. Different strains of S. cerevisiae can produce significantly different flavour profiles when fermenting the same must. This is a consequence of both the differential ability of wine yeast strains to release varietal volatile compounds from grape precursors and the differential ability to synthesise de novo yeast-derived volatile compounds [12], [13], [14], [15]. Therefore, selecting the proper yeast strain can be critical for the development of the desired wine style [7]. For this reason, modern wine makers prefer to employ selected yeast strains. For the production of young wine, the wineries select yeast strains that produce both the high levels of the esters and acetates needed for the desirable fruity taste and the low levels of higher alcohols that contribute negatively to aroma [11]. Moreover, employing selected starter yeast cultures provides technological advantages such as guaranteeing that the must ferments in the correct way. On the other hand, the use of autochthonous yeast strains, besides promoting biodiversity, is rather preferable since they are better acclimated to the environmental conditions and assure the maintenance of the typical sensory properties of the wines of any given region.

The aim of this work is to select the best yeast strains among autochthonous and commercial to obtain organic wines with high organoleptic qualities.

Section snippets

Yeast strains and yeast implantation control

Five different strains of S. cerevisiae were tested; four autochthonous strains were compared with a commercial yeast strain frequently employed by the winery for the vinification of red wines. The commercial yeast was Excellence XR (XR) (Lamothe-Abiet, Bordeaux, France) and the autochthonous yeasts were coded as MY, NY, OY and AGY. The commercial yeast was selected in accordance with the winery's preferences and the autochthonous strains were isolated from the same cellar and the neighbouring

Yeast analysis and fermentation kinetics

Forty yeast strains were isolated from the fresh juice before yeast inoculation. According to PCR-RFLP of the 5.8S rDNA gene, 38 isolates corresponded to non-Saccharomyces strains, and the remainder to the Saccharomyces genus. Further analysis characterised the last strains as the commercial yeast Excellence XR, frequently used by the winery.

To determine the implantation of the inoculated yeast in each vat, samples at different fermentation stages were analyzed by mitochondrial DNA RFLP. Fig. 1

Conclusions

The concentrations of most of the volatile compounds were significantly influenced by the yeast strain. Furthermore, because the implantation percentage of the strain sown in each vat was 100%, we can say that each strain tested is responsible for the volatile profile of the resulting wine. The differences observed in the volatile composition of wines obtained from different yeast strains appear to be quantitative rather than qualitative.

The results obtained in the sensory analysis suggest that

Acknowledgement

The authors are grateful for the financial assistance of the Andalusian Government.

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