Teresa Arroyo

Biotechnological potential of non-Saccharomyces yeasts isolated during spontaneous fermentations of Malvar (Vitis vinifera cv. L.)

Non-Saccharomyces yeast species assume an important role in wine flavor. Notwithstanding, the chemical basis for the flavor characteristics of wines from some grape varieties is not yet defined. The value of this work lies in the use of Malvar white grape, an autochthonous variety from Madrid (Spain) winegrowing region to conduct spontaneous fermentations. This is the first time that a comparative characterization of a wide range of non-Saccharomyces species and a comprehensive analysis of these yeast-derived volatiles has been carried out in this grape variety. β-glucosidase and pectinase (polygalacturonase) extracellular activities were tested on agar plates as primary selection criteria among the 504 non-Saccharomyces isolated from Malvar spontaneous fermentations during four consecutive harvests. Analysis of the wines obtained after fermentation using the selected yeast strains indicates that non-Saccharomyces yeasts isolated along the fermentative process seem that could have a positive impact, showing a high variability in the volatile compounds contributing to the organoleptic characteristics of Malvar wines. Torulaspora delbrueckii CLI 918 was defined as the yeast strain with potential interest for its contribution to the aromatic wine profile with flowery and fruity aromas and could be used in mixed starter cultures with Saccharomyces cerevisiae. However, Hanseniaspora guilliermondii increased the volatile acidity and ethyl acetate, but this species along with the genus Pichia and Candida seem to provide a high quantity of extracellular enzymes which may be beneficial in wine making.

Threshold detection of aromatic compounds in wine with an electronic nose and a human sensory panel.

An electronic nose (e-nose) based on thin film semiconductor sensors has been developed in order to compare the performance in threshold detection and concentration quantification with a trained human sensory panel in order to demonstrate the use of an e-nose to assess the enologists in an early detection of some chemical compounds in order to prevent wine defects. The panel had 25 members and was trained to detect concentration thresholds of some compounds of interest present in wine. Typical red wine compounds such as whiskeylactone and white wine compounds such as 3-methyl butanol were measured at different concentrations starting from the detection threshold found in literature (in the nanograms to milligrams per liter range). Pattern recognition methods (principal component analysis (PCA) and neural networks) were used to process the data. The results showed that the performance of the e-nose for threshold detection was much better than the human panel. The compounds were detected by the e-nose at concentrations up to 10 times lower than the panel. Moreover the e-nose was able to identify correctly each concentration level therefore quantitative applications are devised for this system.

Evaluation of Wine Aromatic Compounds by a Sensory Human Panel and an Electronic Nose

A comparative study between the perception and recognition thresholds of volatile components calculated for an electronic nose and a human sensory panel is presented. The electronic nose is home-developed for wine purposes and is based on thin film semiconductor sensors. The human sensory panel is formed by 25 tasters with previous experience in wine tasting. Both systems were trained in parallel to detect 17 volatile compounds involved in aromatic and off-flavor notes (grouped under 9 aromatic descriptors) from the threshold concentrations found in the literature (T) to increasing concentrations (T, 2T, and 4T). The results showed that the perception level of the human nose is superior in relation to the electronic nose, but the electronic nose gave better results in the recognition threshold of the some aroma. According to these results, it can be concluded that the electronic nose could be a useful complementary tool to sensory human panels.

Genetic diversity in commercial wineries: effects of the farming system and vinification management on wine yeasts

Aims:  Analysis of the diversity and distribution of wine yeasts isolated from organically and conventionally grown grapes, and during the subsequent fermentation with or without starter cultures in six different commercial wineries.

A long term field study of the effect of fungicides penconazole and sulfur on yeasts in the vineyard

This research deals with how two fungicide treatments against powdery mildew, penconazole as a systematic fungicide and sulfur as an inorganic broad-spectrum fungicide, affect the diversity and density of wine yeasts associated with grape berry surfaces and subsequent spontaneous fermentations. Unlike other studies in this area, this work aims to evaluate this effect on the population dynamics in the environment, the conditions of which are not reproducible in the laboratory. A long term (three year) sampling plan was thus devised. A minimum inhibitory concentration assay was also carried out in the laboratory in order to prove the influence of these antifungals on yeast populations. While both antifungal treatments (penconazole and sulfur) were similarly effective against powdery mildew, each had a very different effect on yeast populations. Penconazole showed the most negative effect on biodiversity in the vineyard and was the fungicide to which the isolated yeasts showed the greatest sensitivity. This study therefore evidences the suitability of treatment with sulfur, in both conventional and organic viticulture, to preserve the yeast population associated with grape berries, in particular the Saccharomyces cerevisiae species.

Sensory and Olfactometric Profiles of Red Wines after Natural and Forced Oxidation Processes

The aromatic profiles of different Spanish red wines undergoing natural and forced oxidation were examined using sensory, gas chromatography/olfactometry (GC/O), and quantitative analyses. A significant increase in oxidation descriptors such as cognac/brandy/sherry wine or old wine/matured wine was observed after wine oxidation, and wines also lost some of their herbal, fresh, fruity, and flowery notes. This change in the aroma profile was linked to an increase in compounds such as methional, (Z)-2-nonenal, (E)-2-octenal, furaneol, dodecanal, (Z)-whiskey lactone, and o-aminoacetophenone and a decrease of some volatiles with herbal, fruity, and flowery descriptors, such as (Z)-3-hexenol, ethyl hexanoate, and isoeugenol. Quantitative analyses confirmed the importance of aldehydes in the oxidation processes, especially in forced oxidations, where most of the aldehydes reached very high concentrations, such as methional (83.6 μg/L), phenylacetaldehyde (90.2 μg/L), furfural (183.7 μg/L), 5-hydroxymethylfurfural (89.9 μg/L), and 2-methylpropanal (197.7 μg/L).

A Wireless and Portable Electronic Nose to Differentiate Musts of Different Ripeness Degree and Grape Varieties

Two novel applications using a portable and wireless sensor system (e-nose) for the wine producing industry—The recognition and classification of musts coming from different grape ripening times and from different grape varieties—Are reported in this paper. These applications are very interesting because a lot of varieties of grapes produce musts with low and similar aromatic intensities so they are very difficult to distinguish using a sensory panel. Therefore the system could be used to monitor the ripening evolution of the different types of grapes and to assess some useful characteristics, such as the identification of the grape variety origin and to prediction of the wine quality. Ripening grade of collected samples have been also evaluated by classical analytical techniques, measuring physicochemical parameters, such as, pH, Brix, Total Acidity (TA) and Probable Grade Alcoholic (PGA). The measurements were carried out for two different harvests, using different red (Barbera, Petit Verdot, Tempranillo, and Touriga) and white (Malvar, Malvasía, Chenin Blanc, and Sauvignon Blanc) grape musts coming from the experimental cellar of the IMIDRA at Madrid. Principal Component Analysis (PCA) and Probabilistic Neural Networks (PNN) have been used to analyse the obtained data by e-nose. In addition, and the Canonical Correlation Analysis (CCA) method has been carried out to correlate the results obtained by both technologies.

Non-Saccharomyces Yeasts: Biotechnological Role for Wine Production

Non-Saccharomyces yeasts play a substantial role in the early stages of wine fermentation. With the increase in alcohol concentration, indigenous or commercial strains of Saccharomyces cerevisiae take over and complete the transformation of the grape must sugars into ethanol, CO2, and other secondary metabolites. The presence of nonSaccharomyces during the fermentation has an impact on the wine composition, and consequently, their contribution during the fermentation process cannot be ignored. The new challenges to enhance the appeal and value of wine elaborated by traditional technology are being achieved by selecting and using autochthonous non-Saccharomyces and Saccharomyces strains that may enhance regional identity of wines. Greater understanding of yeast biochemistry and physiology is enabling the selection and development of yeast strains that have defined specific influences on process efficiency and wine quality. The aim of this chapter was to show the different aspects of nonSaccharomyces species that may play a positive incidence in the biotechnological process to conduct to wine elaboration.

The phenotypic characterization of yeast strains to stresses inherent to wine fermentation in warm climates

Climate change is exerting an increasingly profound effect on grape composition, microbiology, chemistry and the sensory aspects of wine. Identification of autochthonous yeasts tolerant to stress could help to alleviate this effect.

Yeast Monitoring of Wine Mixed or Sequential Fermentations Made by Native Strains from D.O. “Vinos de Madrid” Using Real-Time Quantitative PCR

There is an increasing trend toward understanding the impact of non-Saccharomyces yeasts on the winemaking process. Although Saccharomyces cerevisiae is the predominant species at the end of fermentation, it has been recognized that the presence of non-Saccharomyces species during alcoholic fermentation can produce an improvement in the quality and complexity of the final wines. A previous work was developed for selecting the best combinations between S. cerevisiae and five non-Saccharomyces (Torulaspora delbrueckii, Schizosaccharomyces pombe, Candida stellata, Metschnikowia pulcherrima, and Lachancea thermotolorans) native yeast strains from D.O. “Vinos de Madrid” at the laboratory scale. The best inoculation strategies between S. cerevisiae and non-Saccharomyces strains were chosen to analyze, by real-time quantitative PCR (qPCR) combined with the use of specific primers, the dynamics of inoculated populations throughout the fermentation process at the pilot scale using the Malvar white grape variety. The efficiency of the qPCR system was verified independently of the samples matrix, founding the inoculated yeast species throughout alcoholic fermentation. Finally, we can validate the positive effect of selected co-cultures in the Malvar wine quality, highlighting the sequential cultures of T. delbrueckii CLI 918/S. cerevisiae CLI 889 and C. stellata CLI 920/S. cerevisiae CLI 889 and, mixed and sequential cultures of L. thermotolerans 9-6C combined with S. cerevisiae CLI 889.