Influence of the yeast strain on Monastrell wine colour

Two commercial yeast strains were assayed during the winemaking process of Monastrell grapes to determine their influence on colour and phenolic composition of the resulting wines during alcoholic fermentation and maturation. The results showed that in 2002, the wines did not present great differences but in 2003 higher colour intensity and phenolic compounds content were detected when one of the commercial strains was used. A discriminant statistical analysis clearly showed that different yeasts led to different wines as regard their chromatic characteristics.Industrial relevanceThe importance of yeast in winemaking is extensively known since they are responsible for the transformation of sugars into ethanol and for the formation of the most significant aroma compounds in wines. However, they may also participate in wine colour and this role is usually not taken into account in the wine industry. The choice of a yeast strain is an important factor since these microorganisms have the capacity to retain or adsorb phenolic compounds and, on the other hand, yeast may contribute to stabilizing wine colour, as a result of participating in the formation of vitisins during fermentation or liberating mannoproteins that have the capacity to bind to anthocyanins and tannins, protecting them from precipitation. Two commercial yeast strains were assayed during the winemaking process of Monastrell grapes to determine their influence on colour and phenolic composition of the resulting wines during alcoholic fermentation and maturation. The results showed that higher colour intensity and phenolic compounds content were detected when one of the commercial strains was used, both during fermentation and wine aging, and may be used as a tool during winemaking for obtaining stable and highly coloured wines.     

Effects of aging and heat treatment on whole yeast cells and yeast cell walls and on adsorption of ochratoxin A in a wine model system

A wine model was evaluated to determine the influence of aging on the ability of whole yeast cells (WY) and yeast cell walls (YCW) to remove ochratoxin A (OTA). Aging and autolysis were monitored for 214 h in the model wine. The original concentration of OTA in the model wine was 10 microg/liter, and WY and YCW were added at a final concentration of 1 g/liter. YCW mannoproteins were involved in the removal of OTA from the model wine through adsorption mechanisms. Aging affected the capacity of WY to remove OTA, but YCW removal capacity remained constant during aging. A previous heat treatment (85 degrees C for 10 min) of WY and YCW increased their removal capacity and increased the efficiency of the decontamination process.     

Removal of ochratoxin A by wine Saccharomyces cerevisiae strains

The aim of this work was to examine two wine strains of Saccharomyces cerevisiae (Syrena LOCK 0201 and Malaga LOCK 0173 strains) and thermally inactivated biomass of bakery yeast (BS strain) for their ability to remove ochratoxin A (OTA) from model YPG, white grape GM, and blackcurrant BM media. The media was initially contaminated by 1 μg/mL OTA. The influence of OTA on yeast growth parameters, kinetic of fermentation, and amount of ethanol, glycerol, and acids were determined. It was found that both yeast strains were able to decrease the toxin amount in YPG, GM, and BM media. Strain Malaga LOCK 0173 was able to remove 82.8 and 10.7 % ochratoxin A from grape and blackcurrant medium, respectively. In case of Syrena LOCK 0201 strain, the OTA reduction was higher: 85.1 % for grape and 65.2 % for blackcurrant media. From 54.1 to 64.4 % of initial ochratoxin A concentration was removed after the contaminated wine treatment by thermally inactivated baker’s yeast strain (BS) cells. The elongation of lag phase in contaminated YPG medium compared on toxin-free medium was noted. In white grape and blackcurrant medium, the differences between the final cell number, fermentation rate, moreover the ethanol, glycerol, and acids production in the medium with OTA and the control were not statistically significant. The results showed that the application of selected strains of yeasts in winemaking involving raw material contaminated with OTA might reduce the toxin contamination as well as the health risk related to human exposure to this toxin. Moreover, the application of heat-inactivated yeast’s biomass for toxin adsorption gives new possibilities in oenology.     

Surfome analysis of a wild-type wine Saccharomyces cerevisiae strain

The yeast Saccharomyces cerevisiae, besides being an eukaryotic cell model, plays a fundamental role in the production of fermented foods. In the winemaking industry, yeast cell walls may be involved in numerous processes and contribute substantially to the final chemical and sensorial profiles of wines. Nonetheless, apart from mannoproteins, little is known on the protein components of the yeast cell wall and their changes during the fermentation of must into wine. In this work, we performed a dynamic analysis of the cell surface proteome (surfome) of an autochthonous wine yeast strain (previously selected as a wine fermentation starter) by shaving intact cells with trypsin and identifying tryptic peptides by means of nLC-ESI-LIT-MS/MS. Out of the 42 identified proteins, 16 and 14 were found to be specifically expressed in wine yeast surfome at the beginning and at the end of fermentation, respectively. The molecular functions of these specifically expressed proteins might help in explaining their roles in the cell wall as a response to the alcoholic fermentation-related stresses. Additionally, we provided the identification of 20 new potential cell wall related proteins. Globally, our results might provide new useful data for the selection and characterization of yeast strains to be used in the winemaking industry.     

Wine phenolic profile altered by yeast: Mechanisms and influences

Grape phenolic compounds undergo various types of transformations during winemaking under the influences of yeasts, which further impacts the sensory attributes, thus the quality of wine. Understanding the roles of yeasts in phenolics transformation is important for controlling wine quality through fermentation culture selection. This literature review discusses the mechanisms of how yeasts alter the phenolic compounds during winemaking, summarizes the effects of Saccharomyces cerevisiae and non-Saccharomyces yeasts on the content and composition of phenolics in wine, and highlights the influences of mixed cultural fermentation on the phenolic profile of wine. Collectively, this paper aims to provide a deeper understanding on yeast–phenolics interactions and to identify the current literature gaps for future research.     

Release of macromolecules by Saccharomyces cerevisiae during ageing of French flor sherry wine "Vin jaune"

The French flor sherry wine "Vin jaune" spends 6 years and 3 months in the same barrel under a yeast velum. Because of temperature variations in the cellars, this velum sinks partially into the wine and a deposit of dead yeasts cells accumulates in the bottom of the barrels, favouring the formation of new velum. Growth and autolysis occur simultaneously. This study investigated the evolution of macromolecules released by yeasts during the ageing of "Vin jaune" in a model system closely simulating winemaking. It was observed that the release of macromolecules during the formation of the velums by living yeasts was low but greatly increased when the velums fell and yeast viability decreased. The release of macromolecules was then due to the autolysis of dead cells. Analysis of macromolecules during ageing revealed that they contained 73.3-78.5% neutral sugars and 6-7% proteins according to the ageing stage. Their amino acid composition did not change during ageing. A high content of serine and threonine commonly involved in O-glycosidic linkages present in yeast mannoproteins was observed. Throughout ageing, the mannose and glucose contents of macromolecules increased but the ratio of polymeric mannose to glucose decreased. Size exclusion chromatography showed that mannoproteins released in wine were partially hydrolysed by yeast beta-1,3-glucanases freed in wine.     

An invertase fragment responsible for improving the protein stability of dry white wines

The thermoprotective effect of yeast parietal mannoproteins improves the protein stability of white wines aged on their lees (sur lie). The substance responsible for this is an N‐glycosylated, 31.8 kDa mannoprotein that corresponds to a parietal invertase fragment of Saccharomyces cerevisiae. This mannoprotein is released into the wine during autolysis of the lees by the combined action of β‐glucanases from the cell wall and the yeast's vacuolar protease. This mannoprotein may be obtained industrially by extracting yeast mannoproteins using enzymatic digestion of the cell wall with commercially prepared β‐glucanases (Glucanex^TM ‐Novo‐Nordisk). A wine's susceptibility to protein breakdown may be considerably reduced by adding this mannoprotein extract. As a result, less bentonite is needed to stabilise the wine. © 1999 Society of Chemical Industry     

Antioxidant Properties of Sparkling Wines Produced with β-Glucanases and Commercial Yeast Preparations

The aim of this study was to evaluate the in vitro antioxidant potential of sparkling wines produced with β-glucanases, autolysated yeasts, yeast cell walls, and purified mannoproteins. Total antioxidant capacity (measured by 2,2-diphenyl-1-picrylhydrazyl [DPPH] radical-scavenging method and ferric reducing antioxidant power [FRAP] assay), and hydroxyl radical-scavenging activity (HRSA) were higher in the wine samples with coadjuvants (in relation to the control wine). The highest values of antioxidant activity were achieved with purified mannoproteins and, in lesser extent, with β-glucanases. Neutral polysaccharides and total proteins were highly and positively correlated with DPPH, FRAP, and HRSA assays. However, correlations between the levels of each different phenolic family and antioxidant and radical-scavenging activities were not found. β-Glucanase and commercial yeast preparations can be excellent coadjuvants to increase the antioxidant properties of sparkling wines. Practical Application: β-Glucanase and commercial yeast preparations can be excellent coadjuvants to increase the antioxidant properties of sparkling wines. The suggested improvement has significant implication for the production of high added value sparkling wines.     

A new methodology to determine cell wall mannoprotein content and release in wine yeasts

Representing around 40% of the cell wall dry weight, mannoproteins are complex macromolecules structurally composed of polymers of sugar, 98% being mannose, covalently linked to peptides. Along the last two decades, these compounds have gained ground as very relevant molecules in the field of winemaking, mainly due to their positive contributions in the development of appreciated organoleptic features and to their contribution in the chemical stabilization of wine. Several methodologies have been recently proposed to achieve the quantification of these compounds. However, these methodologies are laborious, time consuming and do not allow a global quantification of these macromolecules. In this paper, an easy, reliable and fast forward methodology for the quantification of mannoproteins in model must is proposed and evaluated. Its application in the quantification of mannoproteins content in yeast cell wall is also demonstrated.     

Effect of the addition of β-glucanases and commercial yeast preparations on the chemical and sensorial characteristics of traditional sparkling wine

Sparkling winemaking is an increasing industry in Castilla y León region of Spain. Several trials have been made to improve the techniques in order to offer better products to the market. This study focuses on the evaluation of the influence of different co-adjuvants in the sparkling winemaking process (β-glucanases, autolysated yeasts, yeasts cell walls and purified mannoproteins) by measuring different oenological parameters at 3, 6 and 9?months of ageing after the secondary fermentation. Both physicochemical and sensorial analyses are considered in order to reveal the incidence of these co-adjuvants in the final product. A consumers study has also been carried out with the aim of knowing the possible impact of the co-adjuvants in the market of the so elaborated sparkling wines. β-Glucanases seem to increase the ageing characteristics of the sparkling wines, while yeast derivatives (yeast cell walls and yeast autolysates) improve their fruity and flowery character.     

Interactions of phenolic and volatile compounds with yeast lees,commercial yeast derivatives and non toasted chips in model solutions and young red wines

Ageing of wines on lees, the use of commercial yeast derivative products and the addition of oak chips to wine permit the release of different compounds such as mannoproteins and polysaccharides into wines during yeast autolysis. These compounds released can interact with phenolic compounds and/or aromatic compounds, also modifying wine sensory perception. For that reason, the aim of this work was to evaluate the interaction of phenolic and volatile compounds of wines with yeast lees, non-toasted oak wood chips and different commercial yeast derivative preparations in model wine solutions and in a real red wine. The results found in this study have shown that most of the phenolic and volatile compounds studied are adsorbed by wood and bound by lees in model wine solutions. However, in the model wines in general, the commercial yeast derivative products studied only interacted with the volatile compounds but not with the phenolic compounds. The adsorption of the phenolic compounds occurred in the first 15 days of treatment, remaining constant for 2 months; however, in the case of volatile compounds, these compounds initially displayed a retention effect, but after 30–60 days, the release of the previously bound compounds was instigated. The adsorption effect on the phenolic and volatile compounds in the model wine solution was not always the same as in the red wine studied, which highlights the important presence of other wine compounds in these interactions.     

Distribution of phenolic yeasts and production of phenolic off-flavors in wine fermentation

The activity of wine yeasts to decarboxylate ferulic and p-coumaric acids is one of their biological properties related to the production of phenolic off-flavors (POF) in wine-making. We examined POF productivity in 116 strains of wine yeast, 74 strains of wild yeast (Saccharomyces cerevisiae) and 23 strains of non-Saccharomyces yeast, and found that a majority of these yeasts were POF-producing strains. The frequency distribution of POF-producing strains was 81 to 95% in wine yeasts, 85 to 97% in wild yeasts and 78 to 83% in non-Saccharomyces yeasts based on the POF test with addition of ferulic and p-coumaric acids to grape juice medium. The Rhodotorula, Candida, Cryptococcus, Pichia, Hansenula, and Brettanomyces strains had high or moderate POF productivity among the 20 non-Saccharomyces species. The decomposition rate of ferulic acid correlated with POF production and the critical concentration of phenolic acid (free form) in grape must was estimated to be more than 10 mg/l. Segregation of POF phenotype and Southern blot analysis of phenolic wine yeasts suggest that POF production is controlled by the POF gene (PAD1). The results showed the frequent distribution of phenolic yeasts in the wine-making environment. These suggest the importance of controlling POF production by using wine yeast strains of low POF productivity. The grapes must be prepared by a suitable process to prevent the increase in phenolic acid content.     

Reduction of Ochratoxin A Levels in White Wine by Yeast Treatments

This paper describes the abilities of 21 yeast strains isolated from six different wine‐grapes of Turkey to bind ochratoxin A (OTA). Viable (10⁸ CFU/mL) and heat‐treated yeast cells were incubated both in phosphate‐buffered saline (PBS) and white wine containing 10 ng OTA per mL for 4 h at 25°C. After centrifugation, the concentration of OTA was measured in the supernatant fraction using a high‐performance liquid chromatography system coupled with fluorescence detector. The adsorption abilities of OTA by viable yeast strains within 4 h ranged from 1.96 to 26.11% in PBS. On the other hand, a slight decrease was observed in the percentage of OTA removal by yeast strains in white wine when compared to their activity in PBS. The addition of yeasts at 10⁸ CFU/mL resulted in a reduction to a maximum of 21.40% in white wine, with respect to the control. Among the yeasts, Candida famata D7 was found to be the most efficient binder to OTA both in spiked white wine and PBS. In addition, dead yeast cells can potentially be used for removing OTA (a maximum of 30.45%) from white wine.     

Interactions between yeast, oxygen and polyphenols during alcoholic fermentations: Practical implications

During alcoholic fermentation, even when Saccharomyces cerevisiae cells have used the required oxygen for lipid synthesis, they can consume much more oxygen with no detrimental effect on the fermentation process. Under these conditions, most of the superfluous oxygen is consumed by yeasts by the partial functioning of several nonrespiratory oxygen consumption pathways, which are characterized by the production of reactive oxygen species (ROS). When excess oxygen is added to yeast cells, cell sterol content decreases, following the strong oxidation of intracellular sterols. During aging of fermented products in the presence of nonviable yeast lees (harvested at the end of alcoholic fermentation), the lees can consume oxygen for at least 3 years of the aging process. This oxygen consumption by yeast lees is related to moderate oxidation of yeast membrane lipids by the action of free radicals, strongly decreasing sterols in the yeast lees. The biochemical reactions involved in the oxygen consumption pathways during alcoholic fermentation may be the same as those responsible for oxygen consumption observed in yeast lees. Therefore, the cross-reactivity of complex plant polyphenols, tannins and yeast towards oxygen can easily occur during technological processes (alcoholic fermentation and wine aging). The micro-oxygenation of yeasts releases ROS during alcoholic fermentation and may favour the oxidation of wine phenolic compounds. As yeasts have much higher affinities for oxygen than plant polyphenols, viable yeast and yeast lees compete with phenolic compounds and then hinder the wine aging process. Also, the partial adsorption of plant polyphenols on yeast occurs during alcoholic fermentation, which modifies the overall reactivity of yeast and polyphenols towards oxygen.     

Oenological versatility of Schizosaccharomyces spp.

The biodiversity of non-Saccharomyces yeasts is currently a topic of great interest. The possibility of their use in winemaking has led to much research into the metabolic and structural properties of some of these yeasts, such as those belonging to Torulaspora, Pichia, Hanseniaspora and Hansenula. The present work reviews our knowledge of the genus Schizosaccharomyces, the use of which in winemaking has recently been discussed at the International Organisation of Vine and Wine. However, despite offering the advantage of malic dehydrogenase activity, plus a wall structure that ensures the autolytic release of mannoproteins and polysaccharides during ageing over lees, only one commercial strain of Schizosaccharomyces pombe is currently available.     

Colour correction in white wines by use of immobilized yeasts on κ-carragenate and alginate gels

Pale white wines of the sherry type were subjected to different colour correction treatments based on the use of gel beads consisting of variable proportions of yeasts immobilized on two different polysaccharides (κ-carragenate and alginate). All treatments were found to reduce colour in the control wine, the reduction increasing in a non-proportional way with the increase in yeasts concentration and the decrease in polysaccharide/yeasts ratio. On the same polysaccharide/yeast ratios, κ-carragenate gels proved more efficient than alginate gels. Except for some acids, the concentrations of phenolic compounds were reduced by all treatments (especially those involving κ-carragenate). Based on their colour-correcting ability, moderate retention of human healthy phenolic compounds and similarity to activated carbon in sensory terms, κ-carragenate gels containing a 2 g/L concentration of yeasts in a 2:2 polysaccharide/yeasts ratio represent an effective alternative to fining agents traditionally used in the production of white wines.     

A simple method for total quantification of mannoprotein content in real wine samples

Mannoproteins released by yeast cells throughout the winemaking process contribute in several ways to improve wine quality. For this reason, some winemaking practices have been developed in order to increase the mannoprotein content of wine. However, monitoring of mannoprotein content of wine during these processes, or even mannoprotein quantification in the final wines, is an analytical problem not easily solved so far. Here, we report a simple and accurate method for mannoprotein quantification in wines. The method involves isolation of wine polysaccharides by size exclusion chromatography, acid hydrolysis, elimination of acid by weak anionic exchange solid phase extraction, and analysis of monosaccharides by ion exclusion HPLC. Advantages over previously existing methods include low sample volumes, possibility of parallel processing for multiple samples, absence of precipitation steps, and clear distinction between mannoproteins and other wine polysaccharides.     

A systems biology perspective of wine fermentations

The yeast Saccharomyces cerevisiae is an important industrial microorganism. Nowadays, it is being used as a cell factory for the production of pharmaceuticals such as insulin, although this yeast has long been utilized in the bakery to raise dough, and in the production of alcoholic beverages, fermenting the sugars derived from rice, wheat, barley, corn and grape juice. S. cerevisiae has also been extensively used as a model eukaryotic system. In the last decade, genomic techniques have revealed important features of its molecular biology. For example, DNA array technologies are routinely used for determining gene expression levels in cells under different physiological conditions or environmental stimuli. Laboratory strains of S. cerevisiae are different from wine strains. For instance, laboratory yeasts are unable to completely transform all the sugar in the grape must into ethanol under winemaking conditions. In fact, standard culture conditions are usually very different from winemaking conditions, where multiple stresses occur simultaneously and sequentially throughout the fermentation. The response of wine yeasts to these stimuli differs in some aspects from laboratory strains, as suggested by the increasing number of studies in functional genomics being conducted on wine strains. In this paper we review the most recent applications of post-genomic techniques to understand yeast physiology in the wine industry. We also report recent advances in wine yeast strain improvement and propose a reference framework for integration of genomic information, bioinformatic tools and molecular biology techniques for cellular and metabolic engineering. Finally, we discuss the current state and future perspectives for using 'modern' biotechnology in the wine industry.     

Application of high‐power ultrasounds during red wine vinification

Wine colour is one of the main organoleptic characteristics influencing its quality. It is of special interest in red vinifications due to the economic resources that wineries have to invest for the extraction of the phenolic compounds responsible for wine colour, compounds that are mainly located inside the skin cell vacuoles, where the volatile compounds are also found. The transfer of phenolic compounds from grapes to must during vinification is closely related to the type of grapes and the winemaking technique. During traditional winemaking, grapes are crushed and skin macerated for several days, with pumps overs to facilitate the colour extraction. To increase this extraction, some chemical (maceration enzymes) or physical technologies (thermovinification, cryomaceration, flash‐expansion) can be applied. In this work, a new methodology has been tested. This methodology consists in the application of high‐power ultrasounds to crushed grapes to increase the extraction of phenolic compounds. Crushed grapes were treated with this non‐thermal technology and vinified, with 3, 6 and 8 days of skin maceration time, and the results were compared with a control vinification, where crushed grapes were not subjected to any treatment and were skin macerated during 8 days. The wine chromatic characteristics (determined spectrophotometrically) and the individual phenolic compounds (anthocyanins and tannins, determined by HPLC) were followed during the maceration period, at the end of alcoholic fermentation and after two months in bottle. Also, the wine volatile compounds were determined by GC‐MS. The wines made with ultrasound‐treated grapes showed differences with the control wine, especially regarding total phenol content and tannin content. The wines elaborated with sonicated grapes and with only three days of skin maceration time presented similar concentration of anthocyanins and twice the concentration of tannins than control wines elaborated with 8 days of skin maceration.     

Tailoring wine yeast for the new millennium: novel approaches to the ancient art of winemaking

Yeasts are predominant in the ancient and complex process of winemaking. In spontaneous fermentations, there is a progressive growth pattern of indigenous yeasts, with the final stages invariably being dominated by the alcohol-tolerant strains of Saccharomyces cerevisiae. This species is universally known as the 'wine yeast' and is widely preferred for initiating wine fermentations. The primary role of wine yeast is to catalyze the rapid, complete and efficient conversion of grape sugars to ethanol, carbon dioxide and other minor, but important, metabolites without the development of off-flavours. However, due to the demanding nature of modern winemaking practices and sophisticated wine markets, there is an ever-growing quest for specialized wine yeast strains possessing a wide range of optimized, improved or novel oenological properties. This review highlights the wealth of untapped indigenous yeasts with oenological potential, the complexity of wine yeasts' genetic features and the genetic techniques often used in strain development. The current status of genetically improved wine yeasts and potential targets for further strain development are outlined. In light of the limited knowledge of industrial wine yeasts' complex genomes and the daunting challenges to comply with strict statutory regulations and consumer demands regarding the future use of genetically modified strains, this review cautions against unrealistic expectations over the short term. However, the staggering potential advantages of improved wine yeasts to both the winemaker and consumer in the third millennium are pointed out.