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Biochemistry of Alcoholic Fermentation and Metabolic Pathways of Wine Yeasts

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  • Université Bordeaux
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Abstract

IntroductionSugar degradation pathwaysRegulation of sugar-utilizing metabolic pathwaysMetabolism of nitrogen compoundsReferences

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... Fermentations were performed with four commercial S. cerevisiae strains with diverse aroma bouquet-producing potential and growth characteristics under identical experimental conditions to analyze the nitrogenous compounds that correlated with yeast cell growth and aroma production. In agreement with previous studies (10,29,38,39), these experimental results illustrate significant differences in volatile and nonvolatile production depending on the applied yeast strain. In most cases, the fermentations performed with the Opale strain had the highest maximum and final nonvolatile and volatile concentrations. ...
... Our results suggested, as shown in previous studies, that R2, which, compared with Opale, produces less fusel alcohols and isoacids throughout the fermentation, might more effectively regulate carbon flux (less efficient usage of nitrogen) over time. Moreover, this aspect could be related to nitrogen causing less excretion of excess carbon from core carbon cellular pathways (39). Contrary to VOC product formation, nutrient consumption behavior of nitrogen and sugar compounds was similar among the strains. ...
... Summary of major of VOCs found in wines along with their chemical attributes Ribéreau-Gayon et al.(39). b Swiegers and Pretorius(28). ...
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Genetic background and environmental conditions affect the production of sensory impact compounds by Saccharomyces cerevisiae. The relative importance of the strain-specific metabolic capabilities for the production of volatile organic compounds (VOCs) remains unclear. We investigated which amino acids contribute to VOC production and whether amino acid-VOC relations are conserved among yeast strains. Amino acid consumption and production of VOCs during grape juice fermentation was investigated using four commercial wine yeast strains: Elixir, Opale, R2, and Uvaferm. Principal component analysis of the VOC data demonstrated that Uvaferm correlated with ethyl acetate and ethyl hexanoate production, R2 negatively correlated with the acetate esters, and Opale positively correlated with fusel alcohols. Biomass formation was similar for all strains, pointing to metabolic differences in the utilization of nutrients to form VOCs. Partial least-squares linear regression showed that total aroma production is a function of nitrogen utilization (R2 = 0.87). We found that glycine, tyrosine, leucine, and lysine utilization were positively correlated with fusel alcohols and acetate esters. Mechanistic modeling of the yeast metabolic network via parsimonious flux balance analysis and flux enrichment analysis revealed enzymes with crucial roles, such as transaminases and decarboxylases. Our work provides insights in VOC production in wine yeasts.
... The basic steps of red wine production is shown in Scheme 1. Red winemaking is firstly based on the maceration, which is the process of soaking crushed grape skins, seeds, and, eventually, stems and whose management is one of the most critical aspects; indeed, it is fundamental to extract the colorful and tannic components into wine, but it should not be too prolonged because it could cause an excessive bitter and astringent taste in wine of some varieties, often not well appreciated by consumers (Ribereau-Gayon, Dubourdieu, Doneche, & Lonvaud, 2000;Pinelo, Arnous, & Meyer, 2006;Sokolowsky, Rosenberger, & Fischer, 2015). ...
... After the chosen maceration period, which can depends on the aging purpose of wine, the only partly fermented must is separated from skins and seeds by using a press and the alcoholic fermentation can be completed to almost eliminate sugar residue in the wine (Ribereau-Gayon et al., 2000). ...
... The last phase is the wine aging, that generally consists of different steps (Ribereau-Gayon et al., 2000) including maturation (oxidative aging) and bottling (reductive aging). Moreover, clarification processes and storage in oak barrels (which requires considerable time and financial investment), might be carried out; if the young wine has a lot of grape tannins, the aging in barrels and then in bottles aims to reduce the strength and bitterness of these tannins and rounds out the flavors of the resulting wine (Martín & Sun, 2013). ...
... The production of ATP is linked to the transport of electrons to an oxygen molecule by the cytochromic respiratory chain. This oxygen molecule is the final acceptor of the electrons [53][54][55][56]. ...
... This stage marks the end of the common trunk of glycolysis. The reactions of alcoholic fermentation, glyceropyruvic fermentation or respiration follow, depending on various conditions [56,68,69]. On the other hand, during glycerol assimilation by fungi, yeasts, (heterotrophic) algae or bacteria, by one mole of glycerol there will be the formation of 1 mole of DHAP [73,74] that will be subsequently converted into pyruvate with the reactions mentioned above. ...
... This reaction is catalyzed by the alcohol dehydrogenase using zinc as cofactor. Both final products of alcoholic fermentation, ethanol and carbon dioxide, are transported outside the cell by simple diffusion [54,56,68]. ...
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The majority of environmental problems arise from the use of conventional energy sources. The liability of such problems along with the reduction of fossil energy resources has led to the global need for alternative renewable energy sources. Using renewable biofuels as energy sources is of remarkable and continuously growing importance. Producing bioethanol through conversion of waste and residual biomass can be a viable and important perspective. In the first part of this review, general concepts, approaches and considerations concerning the utilization of the most important liquid biofuels, namely biodiesel and bioethanol, are presented. Unlike biodiesel (specifically first generation biodiesel), the production of bioethanol is exclusively based on the utilization of microbial technology and fermentation engineering. In the second part of this review, the biochemistry of ethanol production, with regards to the use of hexoses, pentoses or glycerol as carbon sources, is presented and critically discussed. Differences in the glycolytic pathways between the major ethanol-producing strains (Saccharomyces cerevisiae and Zymomonas mobilis) are presented. Regulation between respiration and fermentation in ethanol-producing yeasts, viz. effects "Pasteur", "Crabtree", "Kluyver" and "Custers", is discussed. Xylose and glycerol catabolism related with bioethanol production is also depicted and commented. The technology of the fermentation is presented along with a detailed illustration of the substrates used in the process and in pretreatment of lignocellulosic biomass, and the various fermentation configurations employed (separate hydrolysis and fermentation, simultaneous saccharification and fermentation, simultaneous saccharification and co-fermentation and consolidated bioprocessing). Finally, the production of bioethanol under non-aseptic conditions is presented and discussed.
... The rate of decrease in total soluble solids (as °Brix) during the must fermentation differed significantly (p<0.05) with yeast type as the fermentation time progressed, from an intial 20° Brix (Figure 2) The decrease in the sugar concentration during fermentation is mainly attributed to the breakdown by the yeasts and other sugar requiring organisms that may be present (Ribéreau-Gayon et al., 2006). At the end of 96 hours of fermentation there were no significant differences between the °Brix content of must inoculated with the yeast types, even though BYM showed the highest residual soluble solids of 5.2°Brix while LLV had the lowest residual °Brix of 4.9. ...
... Similar trends have been reported by Okunowo et al. (2005) and, Akinwale (1999 in different fruit substrates. Metabolites such as organic acids (acetic acid, formic acids, lactic acids), phenolic compounds, esters and carbon dioxide all play a role in lowering the pH and increasing the total acid content of the must over the course of the fermentation (Onwuka and Awam, 2001; Ribéreau-Gayon et al., 2006). Generally pH and acidity influence the taste of wines by imparting sour tastes to the product.Figure 3. pH as a function of fermentation time and different yeast strains Food Science and Quality Management www.iiste.org ...
... different from each other, even though both had a pale yellow color. Some of the factors that influence the colour development during fruit wine fermentation include concentration of sulphur dioxide and pH of the wine (which affect the extent to which pigment compounds are bleached), the anthocyanin content, the contribution of tannins extracted from the fruit pulp and skin, polymerisation reaction kinetics, enzymatic browning reactions that may occur and the oxidation of pigment compounds present in the substrate (Ribéreau-Gayon et al., 2006). The yeasts used in fermentation do not only have the ability to affect the fermentation rate and the nature and quantity of secondary products formed during alcoholic fermentation but also influence the aromatic characters of the wine (Ribéreau-Gayon et al., 2006). ...
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The goal of this study was to address the problem of large post harvest losses of mangoes by employing yeast fermentation technology to produce a more stable, value-added product in this case fruit wine. The design of the study involved determination of the fermentative capabilities of four commercial yeast types on musts obtained from an improved (Keitt) mango cultivar that is popularly cultivated in some parts of Ghana for export. The characteristics of the mango musts that were monitored included total soluble solids (TSS), pH and total acidity (TA), microbial populations (aerophilic mesophiles, yeasts and Acetic acid Bacteria), alcohol content and colour over the course of the fermentations. Descriptive and hedonic sensory evaluation was carried out on the ferments obtained from all treatments. Results showed that two of the yeast types namely; Red Star Pasteur and Red Star Montrachet displayed superior fermentation characteristics and produced mango wines that were acceptable by both descriptive and affective sensory panels.
... However, some yeast species seem to use the acetic acid present at the beginning of alcoholic fermentation, or even in grape musts, via acetyl-CoA in the lipid-producing pathway [8,20,21]. In wine-making conditions that lead to high levels of volatile acidity, acetic acid is not sufficiently degraded and remains at the end of fermentation. ...
... However, no impact was observed on yeast species distribution in different sampling points (must; must + wine at the beginning or end of fermentation, Figure 2) when compared with the refermentations processes from the other wineries ( Figure 3). This might be due to the SO 2 inhibition that is less pronounced for yeasts than for bacteria [21]. ...
... Cream and green colonies, indicative of the presence of Saccharomyces species, were predominant in all samples analyzed, showing the predominance of this species under refermentation conditions. Their high resistance to stress factors such as ethanol [11], low availability of oxygen [40], yeast killer activity [41] and SO 2 antioxidant and antimicrobial properties [21], may have contributed to the observed predominance. Notably species of Saccharomycodes ludwigii, Schizosaccharomyces pombe, Rhodutorula species, Metschnikowia pulcherrima, Hansenula anomala, Pichia membranefaciens and Brettanomyces intermedius also described as being detected in WL medium, were not found in the samples analyzed. ...
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The level of acetic acid, the main component of volatile acidity, is critical for wine quality. Winemakers have been using a refermentation process to lower the concentration of acetic acid of wines with high volatile acidity, which consists in mixing the acidic wine with freshly crushed grapes or marcs in a proportion of no more than 20-30% (v/v). Though this process implies low costs it harbors the risk of unexpected and detrimental effects on refermented wines. Thus, one challenge to find new solutions for the reduction of excessive volatile acidity is the selection of yeast from refermentation processes of acidic wines to use as starters in a controlled biological process. To this end we set up an isolation protocol with Wallerstein Laboratory Nutrient Agar (WL) to select yeast strains from refermentation processes of acidic wines carried at the winery scale. Among the isolates obtained, 135 were then randomly selected, based on the different colony color pattern and size, and tested for their ability to consume acetic acid in the presence of glucose. For this purpose we used a modified version of a Zygosaccharomyces bailii differential medium containing acetic acid and glucose. Characterization of the isolates obtained in this medium by fingerprinting with primer T3B confirmed three Saccharomyces strains and one non-Saccharomyces strain as predicted by WL and L-Lysine media. Our previous studies revealed that the yeast strains selected by this approach are adequate for the correction of acidic musts and wines with excessive levels of volatile acidity.
... At lab conditions, S. bacillaris strains showed the best growth behaviour when glucose and peptone concentrations were similar, evidencing the role of C/N ratio in modulating yeast growth. This ratio is usually unfavourable in grape musts where the nitrogen source is limited (Ribéreau-Gayon et al., 2006). Regarding nitrogen availability, at tested conditions S. bacillaris reduced the lag phase duration when low nitrogen was present. ...
... g/L). S. cerevisiae species possess a poor ability to degrade malic acid and this is dependent on the must concentration (Ribéreau-Gayon et al., 2006). In this condition 9% of malic acid reduction was observed in EC1118 single-strain fermentation. ...
Article
To obtain beverages with reduced alcohol content, the use of unripe grapes, with low sugar and high malic acid concentration, was recently explored. Due to the low sugar, ethanol and glycerol production is limited during fermentation affecting important sensory aspects such as the palate fullness of these beverages. The high acidity influences their organoleptic quality, as well. So far, only S. cerevisiae starter, used in conventional fermentations, have been tested in this condition, and no selection has been performed to identify alternative yeasts suitable for unripe grape fermentation. S. bacillaris is known for the low ethanol tolerance, high glycerol and moderate volatile acidity production. Therefore, this non- Saccharomyces yeast have been investigated to improve the quality of low-alcohol beverages. Seven S. bacillaris strains were tested in synthetic musts with different sugar and malic acid levels, mimicking natural ripe and unripe grape musts. In all the tested conditions, S. bacillaris produced higher glycerol than S. cerevisiae. In single-strain fermentation at low sugar and high malic acid no S. bacillaris strains was able to transform all the sugars, although the produced ethanol was lower than that at high sugar condition. Therefore, sequential fermentations with S. cerevisiae were evaluated at low sugar and high malic acid. In this condition all the sugars were consumed and a significant glycerol increase was found. These results were confirmed when sequential fermentations were run in natural unripe grape must. Moreover, an increase in malic acid degradation, with respect to EC1118 single-strain fermentation, was observed.
... For instance, total concentrations higher than 400 mg/L negatively contribute to the organoleptic quality of wines [39]. Except for 2-phenylethanol, which imparts a floral aroma [40], the rest of higher alcohols provide unpleasant sensory characteristics [39,40]. ...
... For instance, total concentrations higher than 400 mg/L negatively contribute to the organoleptic quality of wines [39]. Except for 2-phenylethanol, which imparts a floral aroma [40], the rest of higher alcohols provide unpleasant sensory characteristics [39,40]. ...
... From the sensory point of view, concentrations of higher alcohols higher than 400mg/L would contribute negatively to the organoleptic quality of wines (Rapp and Mandery, 1986). With exception of 2-phenylethanol which imparts a floral aroma (Ribereau-Gayon et al., 2006), whose perception threshold is 10mg/L (Rous et al., 1983), the rest of higher alcohols imparts unpleasant sensory characteristics (Rapp and Mandery, 1986;Ribereau-Gayon et al., 2006). The physiological function of higher-alcohol production by yeast is unclear. ...
... From the sensory point of view, concentrations of higher alcohols higher than 400mg/L would contribute negatively to the organoleptic quality of wines (Rapp and Mandery, 1986). With exception of 2-phenylethanol which imparts a floral aroma (Ribereau-Gayon et al., 2006), whose perception threshold is 10mg/L (Rous et al., 1983), the rest of higher alcohols imparts unpleasant sensory characteristics (Rapp and Mandery, 1986;Ribereau-Gayon et al., 2006). The physiological function of higher-alcohol production by yeast is unclear. ...
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The influence of aeration on the fermentative activity of Saccharomyces cerevisiae RIVE V 15-1-416 was studied in order to evaluate the synthesis of fermentation by-products. To achieve this, the strain was cultured in Erlenmeyer flasks and bioreactor containing sterilized and aroma removed apple juice. The chemical compounds produced during fermentations in shaken (200 min-1) and static (without agitation) flasks and bioreactor, all in batch mode, were determined by GC and HPLC. The results showed that agitation of the culture medium dimishes production of total higher alcohols (316.0±27.5mg/L) compared to static cultivation (557.8±28.1mg/L) and enhances slightly ethyl acetate production (75.0±6.5mg/L), whereas on the contrary, the production of acetic acid and glycerol (266.0±8.0mg/L and 2.9±0.2g/L) were higher compared to shaken cultivation (51.0±4.5mg/L and 0.11±0.05g/L) respectively. Batch cultivations carried out in bioreactor with constant air flow of 0.28vvm reported a specific growth rate (μ) of 0.13h-1 and maximum concentration of ethanol of 42.3g/L during aerobic fermentation. Aeration promotes cell growth, diminishes ethanol yield and, provokes acetic acid uptake and succinic acid synthesis whereas malic acid and ethanol were consumed after sugar depletion. The best results in terms of sensory acceptability of the fermented beverage were obtained when cultivated statically. Aeration control during fermentation with this strain can be used to control the synthesis of chemical compounds of sensory importance.
... Acetic acid is the principle component of volatile acidity in fermented beverages (Boulton et al., 1996;Ribéreau-Gayon et al., 2000). At high concentrations, acetic acid gives a negative sensory attribute (vinegarcharacter) to wine, with an acceptable concentration from 0.2 to 0.7 g l -1 . ...
... It is produced not only by spoilage bacteria (lactic acid bacteria and acetic bacteria) but is also formed by yeast during fermentation in the range of 0.1 to 0.3 g l -1 . The biochemical pathway for the formation of acetic acid by wine yeasts has not yet been clearly identifi ed (Boulton et al., 1996, Ribéreau-Gayon et al., 2000. The possible enzyme reactions in yeast that could lead to acetic acid formation are as follows: 1) reversible formation from acetyl Co-A and acetyl adenylate through acetyl Co-A synthetase; 2) cleavage of citrate by citrate lyase; 3) production from pyruvate by pyruvate dehydrogenase; 4) reversible formation from acetyl-phosphate by acetyl kinase and 5) oxidation of acetaldehyde by aldehyde dehydrogenase (Boulton et al., 1996). ...
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Wine aroma is composed of primary, or varietal, aromas that arise directly from the grapes; secondary, or fermentation aromas, aromas produced by yeasts during the alcoholic fermentation; and the tertiary, or maturation bouquet that results from chemical reactions during wine ageing. Organic acids, higher alcohols, low-volatile organic sulphur compounds and esters, with their fruity notes, are signifi cant sensorial components of wine and other fermented beverages and are the primary compounds that form a fermentation bouquet. At low levels, most of these compounds contribute to the perceived wine aroma, but at high levels, they can dominate the aroma, decreasing its complexity. The compounds are released during alcoholic fermentation in variable concentrations depending on the yeast strain, fermentation conditions, and nutrient concentration. The infl uence of nitrogen on alcoholic fermentation and aroma compound formation by yeast, and therefore its effect on wine quality, is discussed herein.
... MLF is a secondary fermentation that transforms the dicarboxylic L-malic acid in the monocarboxylic L-lactic acid, by lactic acid bacteria (LAB). This transformation causes acid reduction, flavour modification and also contributes to microbiological stability of red wine (Ribereau-Gayon et al., 2006). The use of a fast and cheap analytical device (Flores et al., 2013) able to measure the change in MLF progress, such as screen-printed carbon amperometric biosensor, represents a key point for quality wines production because an uncontrolled MLF can causes a risk of wine spoilage and off-flavours development. ...
... D-lactic acid in wine samples is due to heterolactic bacteria which convert sugars, that have not been totally transformed by alcoholic fermentation, in acetic acid and D-lactic acid. This alteration doesn't cause change in quality parameters of wine up to 0.4 g L -1 of D-lactic acid (Gayon et al., 2006). ...
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A lactate oxidase amperometric biosensor was developed and optimized for the malolactic fermentation monitoring during winemaking process. Lactate oxidase enzyme was immobilized on prussian blue modified screen-printed carbon electrode in order to reduce the electrochemical interferences due to the high content of electroactive compounds abundant in wine and must, such as polyphenols and ascorbic acid. The lactate oxidase biosensor developed showed high sensitivity (852 µA M-1) and a detection limit for lactic acid of 0.005 mM (0.45 mg L-1) The operational stability and the life time of the biosensors were also evaluated equal to 8 h and 30 days respectively. Finally the biosensor in flow injection system was used for lactic acid analysis during malolactic fermentation of a red wine and the results were compared with those registered by ion chromatography with good agreement with two sets of data.
... A content of listed aromatic compounds in wines range from a few ng l −1 to hundreds of mg l −1 (Andujar-Ortiz et al., 2009). The presence, abundance and various combinations of volatile compounds can be greatly affected by viticultural practices (variety, cultivation, grape thinning etc.), environmental conditions (climate, soil) and oenological measures (fermentation, yeasts, postfermentation treatments etc.) (Ribéreau Gayon et al., 2006; Welke et al., 2014). Not all volatile compounds present in wine contribute to aroma (Welke et al., 2014). ...
... Most of statistically different physico-chemical characteristics were found in wines from 2011 vintage. But differences between the 2011, 2012 and 2013 vintages are not extensive and most probably caused only by different climatic conditions (Ribéreau Gayon et al., 2006; Vodopivec, 1999). We can confirm that Teran PTP wines contain moderate levels of alcohol (12 vol %), are high in total dry extract and acidity levels, and have surprisingly low contents of both free and total sulphur dioxide in correlation with regulationꞌs demands (Pravilnik, 2004). ...
Article
Teran PTP is a protected wine with a recognized traditional denomination produced from a grapevine variety ‘Refošk’ in winegrowing district Kras in Slovenia (European Union, 2009; Pravilnik, 2008). The aromatic profile of 82 Teran PTP wines produced in years 2011, 2012 and 2013 was monitored. Intotal the content of 16 volatile compounds was determined. The volatile compounds from wine were extracted following the liquid-liquid extraction and determined with a GC-MS method. The odour activity values and relative odour contributions were calculated for each volatile compound identified. Among sensorial important volatiles the highest odour activity values were determined for ethyl octanoate, ethyl hexanoate, isoamyl acetate and ethyl butyrate. Other research papers also showed, that all red wines investigated except one contained ethyl octanoate, ethyl hexanoate, isoamyl acetate and ethyl butyrate above sensory thresholds.
... As we know, the production of ethanol from reduced sugars during alcoholic fermentation occurs along with the production of acetic acid, as well as glycerol. The higher initial content of sugar must increase the production of acetic acid as well as glycerol by yeast metabolism [50,51], even if the initial sugar ranges from 224-268 g/L, which is much lower than that in the musts for ice wine or botrytized wine production. Yeast increases its intracellular ambulation of glycerol to counterbalance the osmotic pressure induced by high sugar content. ...
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The environmental conditions of wine regions determine the flavor characteristics of wine. The characterization of the chemical composition and sensory profiles of young Marselan wines from five wine-producing regions in China was investigated by gas chromatography-mass spectrometry (MS), high-performance liquid chromatography–triple-quadrupole MS/MS and descriptive analysis. Young Marselan wines can be successful discriminated based on concentrations of volatile compounds, but not phenolic compounds, by orthogonal partial least squares discriminant analysis according to regions. Compared to Jiaodong Peninsula (JDP) and Bohai Bay (BHB) regions, there were relatively lower average concentrations of varietal volatiles (mainly including β-citronellol, geraniol, and (E)-β-damasenone) and several fermentation aroma compounds (including isoamyl acetate, octanoic acid, decanoic acid, ethyl decanoate, etc.) but higher levels of acetic acid in Xinjiang (XJ), Loess Plateau (LP), and Huaizhuo Basin (HZB) regions, which were related to their characteristic environmental conditions. Marselan wines from HZB, LP, and XJ regions were characterized by lower L values and higher a and Cab values. Marselan wines from XJ were discriminated from the wines from other regions due to their higher concentrations of several flavonols. Sensory analysis indicated that Marselan wines from HZB region were characterized by relatively low intensities of floral and fruity aromas compared to other regions.
... In response to ethanol exposure, yeasts incorporate this molecule into the membrane, which causes an increase in the membrane fluidity and an alteration in the lipid composition of membranes [22,23]. Sulfite (SO 3 2-) is usually added in the form of potassium metabisulfite (K 2 S 2 O 5 ) and it is used because it inhibits the presence of other undesirable microorganisms, although it also affects yeast cells [24]. ...
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During industrial processes, yeasts are exposed to harsh conditions, which eventually lead to adaptation of the strains. In the laboratory, it is possible to use experimental evolution to link the evolutionary biology response to these adaptation pressures for the industrial improvement of a specific yeast strain. In this work, we aimed to study the adaptation of a wine industrial yeast in stress conditions of the high ethanol concentrations present in stopped fermentations and secondary fermentations in the processes of champagne production. We used a commercial Saccharomyces cerevisiae × S. uvarum hybrid and assessed its adaptation in a modified synthetic must (M-SM) containing high ethanol, which also contained metabisulfite, a preservative that is used during wine fermentation as it converts to sulfite. After the adaptation process under these selected stressful environmental conditions, the tolerance of the adapted strain (H14A7-etoh) to sulfite and ethanol was investigated, revealing that the adapted hybrid is more resistant to sulfite compared to the original H14A7 strain, whereas ethanol tolerance improvement was slight. However, a trade-off in the adapted hybrid was found, as it had a lower capacity to ferment glucose and fructose in comparison with H14A7. Hybrid genomes are almost always unstable, and different signals of adaptation on H14A7-etoh genome were detected. Each subgenome present in the adapted strain had adapted differently. Chromosome aneuploidies were present in S. cerevisiae chromosome III and in S. uvarum chromosome VII–XVI, which had been duplicated. Moreover, S. uvarum chromosome I was not present in H14A7-etoh and a loss of heterozygosity (LOH) event arose on S. cerevisiae chromosome I. RNA-sequencing analysis showed differential gene expression between H14A7-etoh and H14A7, which can be easily correlated with the signals of adaptation that were found on the H14A7-etoh genome. Finally, we report alterations in the lipid composition of the membrane, consistent with conserved tolerance mechanisms.
... Due to the anaerobic conditions accompanying fermentation, acetic acid is formed mainly by oxidation of acetaldehyde with aldehyde dehydrogenase and NADP + as a cofactor. The resulting NADPH participates in lipid biosynthesis [34]. The above explains why these extracellular metabolites were found only in those experimental variants where ethanol biosynthesis was observed. ...
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Understanding the specific response of yeast cells to environmental stress factors is the starting point for selecting the conditions of adaptive culture in order to obtain a yeast line with increased resistance to a given stress factor. The aim of the study was to evaluate the specific cellular response of Saccharomyces cerevisiae strain Ethanol Red to stress caused by toxic by-products generated during the pretreatment of lignocellulose, such as levulinic acid, 5-hydroxymethylfurfural, furfural, ferulic acid, syringaldehyde and vanillin. The presence of 5-hydroxymethylfurfural at the highest analyzed concentration (5704.8 ± 249.3 mg/L) under aerobic conditions induced the overproduction of ergosterol and trehalose. On the other hand, under anaerobic conditions (during the alcoholic fermentation), a decrease in the biosynthesis of these environmental stress indicators was observed. The tested yeast strain was able to completely metabolize 5-hydroxymethylfurfural, furfural, syringaldehyde and vanillin, both under aerobic and anaerobic conditions. Yeast cells reacted to the presence of furan aldehydes by overproducing Hsp60 involved in the control of intracellular protein folding. The results may be helpful in optimizing the process parameters of second-generation ethanol production, in order to reduce the formation and toxic effects of fermentation inhibitors.
... After acetaldehyde, the glycolytic intermediate dihydroxyacetone phosphate is the second most important acceptor of reducing equivalents from NADH within fermenting yeasts. Nevertheless, besides ethanol and glycerol formation, the production of 2,3 butanediol, succinate or D-lactate, which are all originated from pyruvate, can act as useful redox valves during alcoholic fermentation (Camarasa, 2007;Camarasa et al., 2003;de Klerk, 2010;Ribéreau-Gayon et al., 2005). Both succinate and 2,3 butanediol are derivatives from pyruvate. ...
Article
In this study, we presented the first metabolome time course analysis performed among a set of S. uvarum, S. kudriavzevii and S. cerevisiae strains under winemaking conditions. Extracellular and intracellular metabolites, as well as physiological parameters of yeast cells, were monitored along the process to find evidence of different metabolic strategies among species to perform alcoholic fermentation. A thorough inspection of time trends revealed several differences in utilization or accumulation of fermentation by-products. We confirmed the ability of S. uvarum and S. kudriavzevii strains to produce higher amounts of glycerol, succinate or some fusel alcohols and their corresponding esters. We also reported differences in the yields of less common fermentative by-products involved in redox homeostasis, namely 2,3 butanediol and erythritol. 2,3 butanediol yield was higher in must ferment with cryophilic strains and erythritol, a pentose phosphate pathway derivative, was particularly overproduced by S. uvarum strains. Contrary to S. cerevisiae, a singular production-consumption rate of acetate was also observed in S. uvarum and S. kudriavzevii fermentations. Since acetate is a precursor for acetyl-CoA production which is involved in the biosynthesis of membrane lipids, cryophilc strains might take advantage of extracellular acetate to remodel cell membrane as ethanol content increased during fermentation.
... However, excess of NADH is still present as a result of the synthesis of organic acids and some other anabolic reactions required for cell growth. Therefore, there exists an alternative pathway to regenerate NAD + and to prevent redox imbalance in the cell, i.e., glyceropyruvic fermentation with glycerol as its final product (1 mol NADH per mol of glycerol) [33,184]. In better words, glycerol production serves as a sink for electrons under anaerobic conditions. ...
Article
Bioethanol, a prominent biofuel mostly produced industrially by the yeast Saccharomyces cerevisiae, has been among the main pillars of sustainable development in the transportation sector. However, there exist different factors negatively affecting ethanolic fermentation pathway including i.e., microbial contamination, ethanol stress, and byproducts production (CO2, biomass, and glycerol). Removal of these barriers are essential to achieve a more efficient and cleaner production of this eco-friendly commodity. Among various solutions, by reducing glycerol production, i.e., through redirecting carbon flux into bioethanol production pathway, yields beyond optimal values could be expected. The present article strives to review and discuss glycerol production in S. cerevisiae including its significance and metabolisms. Subsequently, over two decades of investigation (1997–2018) aimed at improving ethanol production by blocking glycerol production pathway in S. cerevisiae using metabolic engineering approaches have been presented and comprehensively elaborated. Various metabolic engineering strategies put forth to enhance ethanol production at the expense of glycerol production have been inclusively reviewed. More specifically, the effect of manipulation of the genes GPD, GLT, GLN, GDH, DAK, GCY, ADH, PDC, and GAPN invidually or in combination on decreasing glycerol and improving ethanol production have been reviewed. Overall, it could be concluded that glycerol production was hindered by the deletion of the most important genes in glycerol production, i.e., GPD genes, generally resulting in increased ethanol production. However, this strategy is also accompanied with reduced yeast growth rate or stopped growth owing to the crucial roles of glycerol, e.g., osmoregulation and redox balancing. Therefore, other strategies such as expression of foreign genes (Escherichia coli mhpF/Bacillus subtilis GAPN) and/or overexpression of yeast genes (GTL1, GLN1, GDH) should be considered simultaneously to compensate for the unfavorable impacts of GPD manipulations. The findings reviewed and critically discussed herein could shed light on the various aspects of yeast metabolic engineering to improve ethanol production and could be instrumental in directing future research efforts toward a more efficient and eco-friendly production of bioethanol as a cleaner alternative of its fossil-oriented counterpart
... Saccharomyces cerevisiae is the model microorganism most commonly used in the study of yeast and higher eukaryotic cell physiology [1]. A major substrate for its growth is sugars, which are degraded through an aerobic or anaerobic fermentation process with the production of CO 2 or alcohol and CO 2 , respectively [2]. Nowadays, the biotechnological research and industrial applications of S. cerevisiae have extended far beyond food and beverage production to medicine development, molecular biology and genetics, and environmental protection technologies [3]. ...
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Yeast β-glucan polysaccharide is a proven immunostimulant molecule for human and animal health. In recent years, interest in β-glucan industrial production has been increasing. The yeast cell wall is modified during the fermentation process for biomass production. The impact of environmental conditions on cell wall remodelling has not been extensively investigated. The aim of this research work was to study the impact of glucose and NaCl stress on β-glucan formation in the yeast cell wall during alcoholic fermentation and the assessment of the optimum fermentation phase at which the highest β-glucan yield is obtained. VIN 13 Saccharomyces cerevisiae (S. cerevisiae) strain was pre-cultured for 24 h with 0% and 6% NaCl and inoculated in a medium consisting of 200, 300, or 400 g/L glucose. During fermentation, 50 mL of fermented medium were taken periodically for the determination of Optical Density (OD), cell count, cell viability, cell dry weight, β-glucan concentration and β-glucan yield. Next, dry yeast cell biomass was treated with lytic enzyme and sonication. At the early stationary phase, the highest β-glucan concentration and yield was observed for non-NaCl pre-cultured cells grown in a medium containing 200 g/L glucose; these cells, when treated with enzyme and sonication, appeared to be the most resistant. Stationary is the optimum phase for cell harvesting for β-glucan isolation. NaCl and glucose stress impact negatively on β-glucan formation during alcoholic fermentation. The results of this work could comprise a model study for yeast β-glucan production on an industrial scale and offer new perspectives on yeast physiology for the development of antifungal drugs.
... Abnormally high concentrations of acetic acid in wines can be removed by refermentation. Yeasts are able to metabolize acetic acid during a refermentation process (Ribéreau-Gayon et al., 2000a). Acording to these authors and the works by Vilela-Moura et al. (2008, one third of acidic wine is mixed with two thirds of freshly crushed grapes or of the residual marc from the fermentation of a finished wine (remaining pulp, after draining the newly made wine), such that the VA of this mixture does not exceed 0.73 g/L of acetic acid. ...
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Despite good modern winemaking practices, microbial contaminations could occur. Therefore, quality wine production requires attention to possible sources of contamination during winemaking and aging. Spoilage microorganisms besides affecting wine healthiness can be dangerous for human consumption, by producing biogenic amines and precursors of ethyl carbamate. The main spoilage microorganisms include species and strains of yeasts, lactic acid bacteria and acetic acid bacteria. Defects include bitterness, off-flavors and sensorial visual faults such as film formation, turbidity, viscosity and sediments. Filamentous fungi may be responsible for depreciating wine quality by the production of mycotoxins. Strains selection for performing alcoholic and malolactic fermentations, gathering the best oenological characteristics, may be the first step for achieving wines with good quality. Also the ability of detoxifying mycotoxins, biogenic amines, must be an additional strain selection criterion for winemaking. Optimization of fining treatments, will also be necessary, to remove off-odour, mycotoxins or biogenic amines from wine.
... The wolfberry wines D2 and D1, and the actinidia kolomikta wine E3 exhibited the high histidine level as well. The rest of the fruit wines had its level below 2 mg L À1. Arginine experiences a fast consumption by microorganisms during wine fermentation, and its presence in wine mainly results from the autolysis of yeasts at the end of fermentation (Rib ereau Gayon et al., 2006a). The white grape wine B2 showed high level of arginine (330.12 mg L À1 ) compared to the other grape wines. ...
Article
Amino acids, biogenic amines and ammonium ion are the primary nitrogen sources in fruit wines. Compared to grape wines, our knowledge to their profile in wines made of other fruits is very lack. Fourteen wines made of nine kinds of fruits together with seven grape wines were selected to compare their nitrogen component profile. White grape wines possessed the highest level of total amino acids, followed by red grape wines and then the wines made of the other fruits. Red grape wines contained the highest level of biogenic amines, followed by white grape wines and the wines made of the other fruits. Ammonium ion was also found to be higher in the wines made of grapes. Principal component analysis revealed that the obvious separations existed among the wines made from different types of fruits, indicating that these nitrogen compounds could be served as the indicators to differentiate different types of fruit wines.
... The aforementioned conditions make must from unripe grapes extremely different from conventional musts. The species S. cerevisiae, known to be highly resistant to ethanol (Fleet, 2003) and scarce in transforming malic acid (Ribéreau-Gayon et al., 2006) is well adapted to this environment, but little is known about its ability to develop in unripe grape must. On the contrary, species with low fermentative activity and ethanol resistance, such as S. paradoxus, could be more suitable do develop in this environment. ...
Article
Among the viticultural techniques developed to obtain wine with reduced alcohol content, the use of unripe grapes with low sugar and high malic acid concentration, harvested at cluster thinning, was recently explored. So far, no studies have evaluated the fermentation performances of Saccharomyces in unripe grape musts, in terms of fermentation ability and reducing malic acid contents, to improve the quality of this low-alcohol beverage. In this work, we evaluated 24 S. cerevisiae strains isolated from Italian and Croatian vineyards with different fermentation aptitudes. Moreover, four S. paradoxus were considered, as previous works demonstrated that strains belonging to this species were able to degrade high malic acid amounts in standard musts. The industrial strain S. cerevisiae 71B was added as reference. Sugar and malic acid contents were modified in synthetic musts in order to understand the effect of their concentrations on alcoholic fermentation and malic acid degradation. S. cerevisiae fermentation performances improved when glucose concentration decreased and malic acid level increased. The conditions that simulate unripe grape must, i.e. low glucose and high malic acid content were found to enhance S. cerevisiae ability to degrade malic acid. On the contrary, S. paradoxus strains were able to degrade high amounts of malic acid only in conditions that resemble ripe grape must, i.e. high glucose and low malic acid concentration. In fermentation trials when low glucose concentrations were used, at high malic acid levels S. cerevisiae strains produced higher glycerol than at low malic acid condition. Malic acid degradation ability, tested on the best performing S. cerevisiae strains, was enhanced in fermentation trials when unripe grape must was used.
... It has been shown that several environmental and genetic factors may influence berry diameter, among these are drought stress, nutrient availability, light interception and temperature at various developmental stages [reviewed by Dai et al. (2011)], in addition to seed number (Gayon et al. 2006). A large part of berry diameter variation may be attributed to natural variability within a single bunch (Tarter and Keuter 2005), a single vine and between individual vines. ...
Article
To successfully use berry sorting in winemaking, it is crucial to understand the interaction of physical and chemical composition of berries. The aim of this study was to investigate the relationship between berry diameter and colour and aspects of wine composition, such as titratable acidity, aroma compounds and phenolic substances of Vitis vinifera L. cv. Riesling. In a first trial, berries were sorted into three berry diameter classes with equal TSS concentration and vinified by 70 mL scale fermentation. In a second trial, berries from each of two diameter classes with equal TSS concentration were sorted by berry colour to obtain samples of low a* value and high a* value berries for the respective diameter class, and vinified. In the first trial, wines from smaller berries had lower titratable acidity and a lower concentration of malic acid. In the second trial, wine obtained from berries with higher a* values showed a higher concentration of free C13-norisoprenoids as well as free and glycosylated monoterpenes. Wines from smaller berries in this trial showed a higher concentration of norisoprenoids and a lower pH. Berry diameter and colour are highly variable within single vineyards, vines and single bunches. Sorting by berry size or colour will lead to wines with a pronounced difference in aroma compounds, acidity and α-amino nitrogen. This study shows the relationship between berry diameter or colour and wine quality aspects such as acidity and aroma. Understanding this relationship will assist winemakers to conduct targeted berry sorting.
... Concentraciones de alcoholes superiores sobre 400 mg/L contribuyen negativamente a la calidad organoléptica, especialmente en vinos 65 . A excepción de 2-feniletanol el cual presenta aroma floral 66 , y cuyo valor umbral de percepción es 10 mg/L 67 , los demás alcoholes superiores imparten características sensoriales desagradables 65,66,68 . ...
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The influence of aireation on the fermentative activity of Kloeckera apiculata RIVE 9-2-1 was studied in order to evaluate the production of metabolites of the fermentation. To achieve this, the strain was cultured in Erlenmeyer flasks containing sterilized and aroma removed apple juice, and the chemical compounds produced during fermentation in shaken (200 min-1) and static (without agitation) cultivation were determined. The results showed that the agitation of the culture medium increases production of higher alcohols (till 591.0 mg/L) compared to static cultivation, whereas on the contrary, the production of acetic acid, ethyl acetate and glycerol (260.0 ± 11.0 mg/L, 196.0 ± 10.0 mg/L y 2.6±0.2 g/L) were higher compared to shaken cultivation (222.0 ± 8.0 mg/L, 96.0 ± 4.5 mg/L and 1.8 ± 0.2 g/L) respectively. Batch cultivations carried out in bioreactor with air flux of 25 l/h reported a growth rate (μ) of 0.17 h-1, production of ethanol (12.5 ± 2.0 g/L) and other compounds typically produced during alcoholic fermentation. The concentration of dissolved oxygen in the fermentation medium affects its metabolism thus; insufficient amounts of oxygen would provoke a respirofermentative metabolism. The best results in terms of organoleptic quality of the fermented beverage regarding to aroma, taste and flavour was obtained when fermented in static cultivation. The control of aeration during fermentation can be used to control the synthesis of chemical compounds of sensory impact in the production of fermented beverages.
... The maceration process should be modulated in a way that only useful grape constituents should be dissolved—those positively contributing to wine flavor and aroma. So, the extraction of these desirable substances should be maximal, if not total (Ribereau Gayon et al., 2006). The main objective of the present study is to evaluate the differences between rose biotype and dark violet biotype of Busuioacă de Bohotin variety on the physico-chemical and sensorial characteristics of the analysed wines. ...
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Busuioacă de Bohotin grapes were harvested at technological maturity in 2014, both biotypes (dark violet biotype and rose biotype) being from Huşi vineyard. The wines were obtained by applying four types of maceration processes: maceration-fermentation, microwave maceration, ultrasound maceration and cryomaceration, namely: Vo-control sample (no yeast and enzymes), V1-Maceration-fermentation, V2-Microwave maceration, V3-Ultrasound maceration and V4-Cryomaceration. The wine samples obtained were characterized from a physico-chemical and sensorial point of view, the main objective of the study being to compare the dark violet biotype and rose biotype of the Busuioacă de Bohotin variety. The physico-chemical analyses were done according to the Compendium of International Methods of Analysis of Wine and Musts (OIV, 2013).The sensory evaluation was conducted according the evaluation method originally proposed by the International Union of Oenologists (UIO). The obtained wines are dry wines with a reducing sugar content between 1.84 g/l (minimum) for dark violet biotype (V2 sample) and 2.18 g/l (maximum) for rose biotype (V1 sample). In terms of alcohol concentration, the highest values were recorded at the dark violet biotype with a maximum of 14.9 % vol. and a minimum of 13.91 % for rose biotype. Sensory analyses revealed that the highest intensity of flavours had the dark violet biotype of Busuioacă de Bohotin variety. It was observed that there were found major differences between the two biotypes of Busuioacă de Bohotin variety on physico-chemical and sensory characteristics, the highest value for all the characteristics being recorded by the dark violet biotype.
... Pinot Noir (Vitis vinifera L.) is known as a red grapevine cultivar with tight bunches, in which the mechanical pressure of adjacent berries may disrupt cuticle waxes and damage berry skins, thus making such areas liable to a higher incidence of microbial attack (Hed et al. 2009). In general, the grapevine pathogens of major economic importance are downy mildew (Plasmopara viticola), powdery mildew (Erysiphe necator) and the so-called bunch rot or grey mould (Botrytis cinerea) (Ribéreau-Gayon et al. 2006), with the latter being one of the most frequent problems in Pinot cultivars. Botrytis cinerea development, alone or associated with other microorganisms, can severely impact grape composition and consequently also that of wine. ...
Article
Background and AimsThe grapevine canopy microclimate, particularly temperature and relative humidity, is of crucial importance for predisposing grapes to lower or greater incidence of microbial infections. Because of global warming, the widely adopted leaf removal at veraison causes an increase in the temperature of the grape berry surface, leading to sunburn and deterioration of berry composition. Seeking a good alternative, a novel, pre-flowering leaf removal was studied and compared with post-flowering approaches using a multidisciplinary approach.Methods and ResultsThe effect of timing of leaf removal on the microbial ecology was studied in a Pinot Noir vineyard during two extremely different vintages. The effectiveness of leaf removal in suppressing Botrytis cinerea was compared with that of fungicide application. Bunch compactness and potential for cost and energy savings were calculated. The results showed that earlier leaf removal offers greater potential for successful control of microbial infections. Pre-flowering defoliation also led to lower bunch compactness (16–18%) accompanied by a substantial yield reduction (30% in 2010 and 24% in 2011).Conclusions In addition to improved microbial control, the lower yield from pre-flowering defoliation can eliminate the need for bunch thinning and consequently reduces total energy consumption; thus, the technique can be considered to have good potential for more sustainable and cost-effective management of the vineyard, saving 27% on costs and as much as 46% on energy.Significance of the StudyThe sustainability of a novel pre-flowering defoliation in Pinot Noir was evaluated by studying the microbial ecology of the vineyard and by calculating the potential savings from reduction in spraying and energy.
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This study optimized ethanol production from sweet sorghum stem juice (SSJ) by Saccharomyces cerevisiae NP01 under very high gravity (VHG) fermentation in 500-mL air locked flasks at 30 °C. Response surface methodology based on a Box-Behnken design was employed to optimize initial sugar (267 g/L), urea (3.24 g/L), and cell concentration (1.32 × 108 cells/mL) for maximization of ethanol concentration (PE), productivity (QP), and sugar consumption (%SC). The experimental values (PE, 119.29 g/L; QP, 2.49 g/L.h and %SC, 91.83%) under optimal conditions were close to the predicted values, verifying the optimization process. Aeration (2.5 vvm for 4 h) increased viable cell counts and decreased glycerol production (a by-product), but not fermentation efficiency. An osmoprotectant (40 mM potassium chloride combined with 10 mM potassium hydroxide, KCl/KOH) at 30 °C had no positive effect on ethanol fermentation efficiency. However, at 25 °C, the osmoprotectant increased PE from 106 to 116 g/L and ethanol yield from 0.46 to 0.49 g/g. At 35-37 °C, it prolonged cell viability, increasing PE by 5-12 g/L and %SC by 3-8% without affecting ethanol yield. However, at 39 °C, no positive impact occurred on ethanol fermentation efficiency. The findings from this study, particularly the optimized fermentation conditions and stress tolerance strategies, could guide the scale-up to an industrial level of bioethanol production from sweet sorghum stem juice or other feedstocks using VHG fermentation, contributing to the development of more efficient and sustainable biofuel production processes.
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Fossil fuels are a major contributor to climate change and environmental pollution, and as the demand for energy production increases, alternative sources are becoming more attractive. Bioethanol reduce reliance on fossil fuels and can be compatible with the existing fleet of internal combustion engines. Bioethanol is typically produced via microbial fermentation of fermentable sugars. Traditional feedstocks (first-generation) include cereal grains, sugar cane, and sugar beets. However, due to concerns regarding food sustainability, lignocellulosic (second-generation) and algal biomass (third-generation) feedstocks have been investigated. Technologies such as Simultaneous Saccharification and Fermentation (SSF), Separate enzymatic Hydrolysis and Fermentation (SHF) and Fed-batch Fermentation for bioethanol hold tremendous potential for the production of bioethanol. The aim of this review focuses on the technologies and factors affecting bioethanol production and its commercialization.
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Fermentation employing Saccharomyces cerevisiae has produced alcoholic beverages and bread for millennia. More recently, S. cerevisiae has been used to manufacture specific metabolites for the food, pharmaceutical, and cosmetic industries. Among the most important of these metabolites are compounds associated with desirable aromas and flavors, including higher alcohols and esters. Although the physiology of yeast has been well‐studied, its metabolic modulation leading to aroma production in relevant industrial scenarios such as winemaking is still unclear. Here we ask what are the underlying metabolic mechanisms that explain the conserved and varying behavior of different yeasts regarding aroma formation under enological conditions? We employed dynamic flux balance analysis (dFBA) to answer this key question using the latest genome‐scale metabolic model (GEM) of S. cerevisiae. The model revealed several conserved mechanisms among wine yeasts, for example, acetate ester formation is dependent on intracellular metabolic acetyl‐CoA/CoA levels, and the formation of ethyl esters facilitates the removal of toxic fatty acids from cells using CoA. Species‐specific mechanisms were also found, such as a preference for the shikimate pathway leading to more 2‐phenylethanol production in the Opale strain as well as strain behavior varying notably during the carbohydrate accumulation phase and carbohydrate accumulation inducing redox restrictions during a later cell growth phase for strain Uvaferm. In conclusion, our new metabolic model of yeast under enological conditions revealed key metabolic mechanisms in wine yeasts, which will aid future research strategies to optimize their behavior in industrial settings.
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Saccharomyces cerevisiae is a highly fermentative species able to complete the wine fermentation. However, the interaction with other non-Saccharomyces yeasts can determine the fermentation performance of S. cerevisiae. We have characterised three rare non-Saccharomyces yeasts (Cyberlindnera fabianii, Kazachstania unispora and Naganishia globosa), studying their impact on S. cerevisiae fitness and wine fermentation performance. Using a wide meta-taxonomic dataset of wine samples, analysed through ITS amplicon sequencing, we show that about a 65.07% of wine samples contains Naganishia spp., a 27.21% contains Kazachstania spp., and only a 4.41% contains Cyberlindnera spp; in all cases with average relative abundances lower than 1% of total fungal populations. Although the studied N. globosa strain showed a limited growth capacity in wine, both K. unispora and C. fabianii showed a similar growth phenotype to that of S. cerevisiae in different fermentation conditions, highlighting the outstanding growth rate values of K. unispora. In mixed fermentations with S. cerevisiae, the three yeast species affected co-culture growth parameters and wine chemical profile (volatile compounds, polysaccharides and proteins). K. unispora DN201 strain presents an outstanding capacity to compete with S. cerevisiae strains during the first stage of wine fermentation, causing stuck fermentations in both synthetic and natural grape musts.
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Wine has very rich and complex aromas but is paradoxically obtained from grape juice that has very little odor itself. This aromatic transformation is mainly due to the action of yeasts during the alcoholic fermentation. First, yeasts produce secondary metabolites that give to wines its basic “winy” characteristic. Second, some enzymatic activities may transform nonodorous compounds of certain grape varieties into varietal aromas, giving the specific characteristics of “cépage.” Depending on the yeast strain, the concentration of aromatic molecules is determined, modifying the organoleptic perception of wine. The enzymatic activities of yeast metabolism and their genetic control have been widely studied, allowing genetic selection approaches as well as molecular engineering for selecting more specialized commercial starters.
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Wine fermentation is an ancient biotechnological process mediated by different microorganisms such as yeast and bacteria. Understanding of the metabolic and physiological phenomena taking place during this process can be now attained at a genome scale with the help of metabolic models. In this chapter, we present a detailed protocol for modeling wine fermentation using genome-scale metabolic models. In particular, we illustrate how metabolic fluxes can be computed, optimized and interpreted, for both yeast and bacteria under winemaking conditions. We also show how nutritional requirements can be determined and simulated using these models in relevant test cases. This chapter introduces fundamental concepts and practical steps for applying flux balance analysis in wine fermentation, and as such, it is intended for a broad microbiology audience as well as for practitioners in the metabolic modeling field.Key wordsConstraint-based metabolic modelingGenome-scale network reconstructionWine fermentation Saccharomyces cerevisiae Oenococcus oeni Metabolic flux
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Economic, social, and political strength, development and activation depend upon the energy-related issues, demand, and the best solutions for the same. When the energy consumption patterns vary and the demand for the production increases the ways and means of energy do change with the pace of time and the fossil fuels were replaced by the diversified and focused on energy generation through nonrenewable sources. Bioethanol has been identified as the best alternate for the petroleum gasoline in the world, and it saves fossil fuels depletion and remedies of the greenhouse gases and employment opportunities. Residues of the food crops, grains, edible and nonedible seeds and vegetable oils may be the main feedstock for the biofuels in the world. Different feedstock with respect to the local and international trends of production of ethanol is mentioned and compared in this study. Impact of the production and the policy of bioethanol is worth discussed in the presentation. For the developing world, the food item being used for the production of bioethanol are discouraged and wastes or byproducts are preferred in this regard. Developing countries have shown their interest in the enhanced production of biofuels and many collaborative projects are in progress and policies, legislation is being formulated locally and international.
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The interaction between wine tannins and saliva proteins is responsible for wine astringency perception, producing a depletion of salivary proteins and changes on oral friction. In sensorial terms, astringency is described as a dryness and puckering sensation in the mouth, which is related to the "structure" or "body" of red wines. However, these last descriptors, as structure or body, are perceived during wine tasting and commonly related to wine viscosity. To address these differences on sensory response, we hypothesize that tannin-protein interactions could be a key factor involved in the viscosity of red wines/saliva mixtures, just as they are for astringency. We used a rheological method to study the impact of tannin-protein interaction on the viscosity of model wine-saliva systems. Mixtures of model saliva based on mucin and typical astringent compounds, as commercial tannins and gallic acid, were evaluated for their rheological behavior. The viscometric flow of the fluid mixtures was determined, and subsequently, the viscosity was evaluated at a shear rate of 60 s-1 . It was observed that red wines/saliva mixtures exhibit non-Newtonian flow and ascending tannin doses led to an increase in the apparent viscosity. Nephelometric analysis demonstrate that tannin-mucin aggregates were formed, which suggests that these complexes were potentially responsible for the viscosity increases, modifying the rheological behavior of these mixtures. Results from this work propose that tannin-protein interactions are also involved in the underlying mechanism of thickness perception of red wines and rheology could be a complementary instrumental technique for wine mouthfeel characterization. This article is protected by copyright. All rights reserved.
Chapter
Organoleptic characteristics of wine, aroma and flavour, are the most important characteristics that define the differences among the vast array of products throughout the world. Yeasts have a prominent role in determining the chemical composition of wine by several mechanisms: by producing enzymes that transform neutral grape compounds into flavour active compounds (pre-fermentative aroma), secondly by producing many hundreds of flavour active, secondary metabolites (fermentative and post-fermentative aroma) and lastly by extracting flavour components from grape solids and by autolytic degradation of dead yeast cells. These reactions vary with the yeast species and strains contributing to the fermentation. This review aims to present an overview on major achievements of yeast role in the formation of wine flavour. Firstly we illustrate the yeast metabolic activities involved in wine aroma production in function of wine styles as well as the main factors affecting flavour quality of wine. Furthermore, the influence of starter cultures (single or mixed) on wine flavour is discussed. Finally, novel methodologies to select wine yeasts in function of their influence on wine aroma are also summarized.
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The book integrates the fundamental factors that determine current and future impacts of biofuels production on water supply and demand in the context of climatic changes. The effects of biofuels production on ground water quality with increasing water scarcity are examined, and the utilization of water sources in the commercial scale production of biofuels are sketched, covering the complete route from growing of crops to biorefinery. Biofuel's chemical composition, characteristics and uses as fuel in terms of water consumption are also investigated. Overall, the diversity of biomass, various technological approaches and microbial contribution are reviewed. Learning objectives on this topic are presented by means of a series of tables and figures in order to guide both professionals and students. The present manuscript deals with biofuel and bioenergy courses and is therefore invaluable to students. The book provides thorough coverage of all industrial aspects of biofuels production, including impacts of climate change and water availability. It will play vital role for industry employees involved in product development, production management, quality management and helpful source to those studying for professional qualification. Academics involved in teaching elements of the subject and persons involved in an environment regulatory capacity would be able to take advantage from this book.
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Biofuel in particular, together with the rising demands for food, have the highest prospects for an increase in agricultural water withdrawals. The water-biofuel relationship is being recognized as backbone of the factors fundamental for the future sustainable supply of water and biofuel. A better understanding of the subject is essential to adopt superior technologies that may improve use of water for biofuel production in efficient way. This chapter presents prospective and future trends of the water-biofuel relationship and impacts of additional water usage in future increased biofuel production. The importance of technological innovation to save water and future impacts on water quantity and especially on water quality will be assessed in terms of safe keeping the environment. The obligation of reusing wastewater and application of undiluted wastewater to grow feedstock for biofuel to save freshwater resources will be analyzed.
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Fossil fuels applications are linked with current widely held environmental issues. The decline of these fuels resources with environmental penalties has compelled for substitutes and usage of renewable biofuel as energy sources; has gained a significant importance in last two decades. Production of biodiesel, biogas and bioethanol from various feedstock, several kinds of wastes, many types of biomass and agricultural residues, is ecological viable and sustainable option. The involvement of biofuel in worldwide transportation fuels seems to be revolving about 5% over the next decade. But, many studies put forward that biofuel may share up to a one fourth of transport fuel supplies by 2050. In the first part of the chapter, advantages and applications of mostly used biofuel is presented. The second part of the chapter keeps concepts about biodiesel. Biogas production and composition has been addressed in third portion. Finally, the production of bioethanol from different feedstock has been discussed. Instability of fossil fuels prices in last decade and environment concerns has increased biofuel production many folds. Such a fast growth has been resulted controversial and raised some concerns over potential water use in production of biofuel.
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Biofuel production process use fresh water collected mainly from surface water flows or from underground natural reservoirs for different activities and it became contaminated with organic and inorganic pollutants. Waste water quality returned to soil and to surface water flows is very poor. To produce one liter of ethanol, 10–17 L of water are consumed. Biofuel production plants are water intensive and there is an upward trend in water consumption. The chapter will describe agricultural and industrial activities involving current water consumption during biofuel production. Major steps of lifecycles for biofuel production pathways: bioethanol from sugarcane molasses and cellulosic feedstock, Biogas from distillery spent wash and Biodiesel from various sources will be evaluated regarding water consumption. The amount of irrigation water used in growth of biofuel feedstock and water consumption for biofuel production through various processing technologies will be analyzed. The vital importance of water management during the feedstock production and conversion stage of the biofuel’s lifecycle will also be discussed.
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Worldwide intensive demand of biofuel as a substitute to fossil fuels has sparked a debate about their advantages especially concerns about human health. Potential health impacts of biofuel are linked to biochemical and chemicals applied in biofuel production processes. Such caustic chemicals are highly hazardous for human health. Other impacts of biofuel come through water pollution; air pollution and use of agrochemicals and pesticides to raise the feedstock. Incomplete burning of sugarcane leaves or residues may results in toxic compounds formation and fine particulates are emitted into atmosphere. The chapter summarizes the basic health effects of biofuel from agriculture cultivation of feedstock to production processes.
Chapter
Groundwater is strategically significant due to its exceeding demand in agriculture, domestic and industrial uses. Global estimates show that approximately 4430 km³ of fresh water resources are abstracted annually for human consumption. Ground water may contain some unwanted matter with the microbes in its natural form but most of the impurities are being added through human activities. Problem of water pollution is more pronounced in localities where biofuel are produced. The generation of obscene wastewater in bulk is a great environmental apprehension. The chapter will discuss how wastewater generated from biofuel production is deteriorating the ground water quality. The treatment ways of the wastewater will also be discussed. Presence of organic and inorganic compounds in wastewaters release from biofuel production facilities making the ground water unfit for human consumption will be explore.
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This paper examines the origins of methanol in grape wine and the quantities typically found in it, as well as in other foods such as unpasteurised fruit juices. The toxicology of methanol and the associated regulatory limits established by competent authorities in various parts of the world are also considered. It is concluded that such limits are not driven by public health considerations and thus authorities are requested to consider the need for methanol analyses to be performed and reported on certificates of analysis as a condition of market entry for wine. Where methanol limits are still deemed to be necessary to achieve policy objectives, authorities are encouraged to establish them in the light of the levels of methanol typically found in grape wines produced by the full array of internationally permitted winemaking practices, and to consider harmonising their limits with those that have already been established by other governments or recommended by appropriate intergovernmental organisations.
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Within this study, bioethanol production from different lignocellulosic resources has been examined through physical, chemical, enzymatic/microbiological pretreatments and their combinations via different microorganisms. Different agricultural residues and aquatic plants have been used as raw material, and carbohydrate obtaining ratios have been analyzed for bioethanol production. There were three different kind of microorganism that used for the experimental sets (Saccharomyces cerevisiae, Pichia stipitis ve Clostridium thermocellum), and their ethanol yields have been compared. According to the results, C reactors has the lowest yield of carbohydrate conversion, while K reactors, which had physical, chemical (NaOH) and enzymatically (cellulase) pretreatments, has the highest yield. K reactors’ ethanol yield has been determined as 4 times higher than C reactors’. The most carbohydrate consumption and bioethanol production amount have been observed from Kbuğday reactor with 8.33 mg/ml, and 3.36 mg/ml, respectively. In Set III, any pretreatment methods have not been carried out for the raw materials but microorganism called C. thermocellum, and ethanol conversion yield has been compared with raw cellulose conversion yield. In Set III, the highest ethanol production amount has been obtained from the reactor which used corn silage with 0.25 mg/ml. The highest yields have been obtained in Set I with 49.77 % from Esümbül, and in Set II wit 50.40 % from Esilaj. according to consumed carbohydrate and produced bioethanol concentrations.
Article
The fermentative activity of Saccharomycodes ludwigii RIVE 16-1-5 was studied in order to evaluate its importance in fermentation processes. The results demonstrated that the strain ferments monosaccharides very well, and also sucrose and maltose. Its fermentative activity was not inhibited even at sodium metabisulphite concentrations of 200 mg/L in the culture medium. Furthermore, it was able to produce ethanol up to 6.88±0.1% (v/v). Agitation of the culture medium enhances the production of higher alcohols (843.7mg/L), but diminishes the production of glycerol (0.18±0.2 g/L) and acetic acid (56.0±8.5 mg/L). In addition, synthesis of ethyl acetate in shaken culture (130.0±8.0 mg/L) was higher compared to that in static culture (without agitation). During batch cultivation carried out under aerated conditions, the growth rate p reached a value of 0.11 h-1. The oxygen concentration in the medium would affect the yeast metabolism, thus insufficient amounts of oxygen would provoke a respiro-fermentative metabolism with production of ethanol, higher alcohols, esters and acetic acid. Aeration control during fermentation is an important tool to control the balance between the respiratory and fermentative activity. Finally, the best results of sensory quality related to aroma, flavor and smell were obtained in static culture.
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The changes of Nero di Troia wines submitted to micro-oxygenation or treatment with oak chips were studied. Oak chips favoured polymerization reactions (SPP, LPP, I HCl, polymeric phenols, and polymeric pigments, respectively +28, +67, +44, +60, and +73 % in comparison with the untreated wines, 12 months after racking). The polymerization reactions increased colour stability (colour intensity, and % of red and blue colour of the oak-treated wines were +11, +2, and +10 % compared to the control). At the end of ageing, the oak-treated wines had the highest concentrations of alcohols, carbonyl compounds, and lactones, while the highest contents of acids and esters were detected in the micro-oxygenated wines. The sensory profile of the oak-treated wines was characterized by the attenuation of floral, fruity, and vinous attributes. Concerning the phenolic profile, micro-oxygenated wines showed the highest concentrations of anthocyanins (+23 % respect to the untreated samples and +306 % respect to the oak-treated ones) and of flavan-3-ols (+24 % respect to the untreated samples and +95 % respect to the oak-treated ones). Micro-oxygenation reduced astringency and herbaceous character and intensified spicy and fruity flavours.
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