Enological functions of parietal yeast mannoproteins

Yeast cell wall mannan structural features, biological activities, and production strategies

Mannan and outer structural yeast cell wall polysaccharides have recently garnered attention for their health defense and cosmetic applications. In addition, many studies have confirmed that yeast cell wall mannans exhibit various biological activities, such as antioxidant, immune regulation, reducing hyperlipidemia, and gut health promotion. This paper elucidates yeast cell wall mannan structural features, biological activities, underlying molecular mechanisms, and biosynthesis. Moreover, mannan-overproducing strategies through yeast strain engineering are emphasized and discussed. This review will provide a scientific basis for yeast cell wall mannan research and industrial applications.

Optimal Extraction and Deproteinization Method for Mannoprotein Purification from Kluyveromyces marxianus

Background

Mannoproteins, mannose-glycosylated proteins, play an important role in biological processes and have various applications in industries. Several methods have been already used for the extraction of mannoproteins from yeast cell-wall. The aim of this study was to evaluate the extraction and deproteinization of mannan oligosaccharide from the Kluyveromyces (K.) marxianus mannoprotein.

Methods

To acquire crude mannan oligosaccharides, K. marxianus mannoproteins were deproteinized by the Sevage, trichloroacetic acid, and hydrochloric acid (HCL) methods. Total nitrogen, crude protein content, fat, carbohydrate and ash content were measured according to the monograph prepared by the meeting of the Joint FAO/WHO Expert Committee and standard. Mannan oligosaccharide loss, percentage of deproteinization, and chemical composition of the product were assessed to check the proficiency of different methods.

Results

Highly purified (95.4%) mannan oligosaccharide with the highest deproteinization (97.33 ± 0.4%) and mannan oligosaccharide loss (25.1 ± 0.6%) were obtained following HCl method.

Conclusion

HCl, was the most appropriate deproteinization method for the removal of impurities. This preliminary data will support future studies to design scale-up procedures.

Quality Characteristics of Reduced-Fat Emulsified Sausages Made with Yeast Mannoprotein Enzymatically Prepared with a β-1,6-glucanase

Mannoproteins, as yeast polysaccharides, have been utilized in food the industry as dietary fibers, emulsifying agents or fat replacers. Mannoprotein MP112, produced from yeast by enzymatic hydrolysis of myxobacterial β-1,6-glucanase GluM, exhibits excellent emulsifying properties in emulsion preparation. In this study, we aimed to examine the application of stable emulsion with the addition of mannoprotein MP112 (MP112 emulsion) to reduce the fat content of sausages. The addition of MP112 emulsion in emulsified sausages significantly reduced the fat content and increased the moisture and protein contents of emulsified sausages without the expense of their good sensory quality. Moreover, the textural properties of sausages were markedly improved with the higher hardness, chewiness and cohesiveness, especially in the 50-75% replacement ratio of MP112 emulsion. On the other hand, MP112 emulsion replacement of animal fat markedly improved the nutritional composition of emulsified sausages; they displayed a higher PUFA/SFA ratio and lower n-6/n-3 ratio due to their saturated fatty acids being replaced by poly-unsaturated fatty acids. Meanwhile, the oxidative stability of sausages was improved linearly, corresponding to the increased replacement ratio of MP112 emulsion. Our results show that mannoprotein-based emulsions could be used as potential fat alternatives in developing reduced-fat meat products.

Effect of Interspecific Yeast Hybrids for Secondary In-Bottle Alcoholic Fermentation of English Sparkling Wines

In sparkling winemaking, only a few yeast strains are regularly used for the secondary in-bottle alcoholic fermentation (SiBAF). Recently, advances in yeast development programs have yielded new breeds of interspecific wine yeast hybrids that ferment efficiently while producing novel flavors and aromas. In this work, the chemical and sensorial impacts of the use of interspecific yeast hybrids for SiBAF were studied using three commercial English base wines prepared for SiBAF using two commercial and four novel interspecific hybrids. After 12 months of lees aging, the chemical and macromolecular composition, phenolic profile, foaming, viscosity and sensory properties of the resulting 13 wines were assessed. Chemically, the yeast strains did not result in significant differences in the main wine parameters, while some differences in their macromolecular contents and sensory characteristics were noticeable. The foamability was mostly unaffected by the strain used; however, some effect on the foam stability was noticeable, likely due to the differences in polysaccharides released into the wines by the yeast strains. The wines exhibited different sensory characteristics in terms of aroma and bouquet, balance, finish, overall liking and preference, but these were mostly attributable to the differences in the base wines rather than the strain used for SiBAF. Novel interspecific yeast hybrids can be used for the elaboration of sparkling wines, as they provided wines with chemical characteristics, flavor and aroma attributes similar to those of commonly used commercial Saccharomyces cerevisiae strains.

Reliable Approach for Pure Yeast Cell Wall Protein Isolation from Saccharomyces cerevisiae Yeast Cells

Saccharomyces cerevisiae yeast is a fungus presenting a peripheral organelle called the cell wall. The cell wall protects the yeast cell from stress and provides means for communication with the surrounding environment. It has a complex molecular structure, composed of an internal part of cross-linked polysaccharides and an external part of mannoproteins. These latter are very interesting owing to their functional properties, dependent on their molecular features with massive mannosylations. Therefore, the molecular characterization of mannoproteins is a must relying on the optimal isolation and preparation of the cell wall fraction. Multiple methods are well reported for yeast cell wall isolation. The most applied one consists of yeast cell lysis by mechanical disruption. However, applying this classical approach to S288C yeast cells showed considerable contamination with noncell wall proteins, mainly comprising mitochondrial proteins. Herein, we tried to further purify the yeast cell wall preparation by two means: ultracentrifugation and Triton X-100 addition. While the first strategy showed limited outcomes in mitochondrial protein removal, the second strategy showed optimal results when Triton X-100 was added at 5%, allowing the identification of more mannoproteins and significantly enriching their amounts. This promising method could be reliably implemented on the lab scale for identification of mannoproteins and molecular characterization and industrial processes for "pure" cell wall isolation.

Structural characteristics of Saccharomyces cerevisiae mannoproteins: Impact of their polysaccharide part

While they have many properties of interest in enology, the structure-function relationships of mannoproteins and the part played by their polysaccharide moiety are not yet well understood. Mannoproteins (MP) extracted with β-glucanase from a laboratory yeast strain (WT), two of its mutants (Mnn2 with unbranched N-glycosylated chains and Mnn4 without mannosyl-phosphorylation), and an enological strain (Com) were purified and thoroughly characterized. The protein moiety of the four MPs had the same amino acid composition. Glycosyl-linkage and net charge analyses confirmed the expected differences in mutant strain MPs. MP-Com had the highest mannose/glucose ratio followed by MP-WT/MP-Mnn4, and MP-Mnn2 (13.5 > 5.6 ≈ 5.2 > 2.2). The molar mass dependencies of R_g, R_h, and [η], determined through HPSEC-MALLS-QELS-Viscosimetry, revealed specific conformational properties of mannoproteins related to their nature of highly branched copolymers with two branching levels. It also clearly showed structural differences between MP-Com, MP-WT/Mnn4, and MP Mnn2, and differences between two populations within the four mannoproteins.

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.

Genome sequencing, annotation and exploration of the SO2-tolerant non-conventional yeast Saccharomycodes ludwigii

BACKGROUND

Saccharomycodes ludwigii belongs to the poorly characterized Saccharomycodeacea family and is known by its ability to spoil wines, a trait mostly attributable to its high tolerance to sulfur dioxide (SO₂). To improve knowledge about Saccharomycodeacea our group determined whole-genome sequences of Hanseniaspora guilliermondii (UTAD222) and S. ludwigii (UTAD17), two members of this family. While in the case of H. guilliermondii the genomic information elucidated crucial aspects concerning the physiology of this species in the context of wine fermentation, the draft sequence obtained for S. ludwigii was distributed by more than 1000 contigs complicating extraction of biologically relevant information. In this work we describe the results obtained upon resequencing of S. ludwigii UTAD17 genome using PacBio as well as the insights gathered from the exploration of the annotation performed over the assembled genome.

RESULTS

Resequencing of S. ludwigii UTAD17 genome with PacBio resulted in 20 contigs totaling 13 Mb of assembled DNA and corresponding to 95% of the DNA harbored by this strain. Annotation of the assembled UTAD17 genome predicts 4644 protein-encoding genes. Comparative analysis of the predicted S. ludwigii ORFeome with those encoded by other Saccharomycodeacea led to the identification of 213 proteins only found in this species. Among these were six enzymes required for catabolism of N-acetylglucosamine, four cell wall β-mannosyltransferases, several flocculins and three acetoin reductases. Different from its sister Hanseniaspora species, neoglucogenesis, glyoxylate cycle and thiamine biosynthetic pathways are functional in S. ludwigii. Four efflux pumps similar to the Ssu1 sulfite exporter, as well as robust orthologues for 65% of the S. cerevisiae SO₂-tolerance genes, were identified in S. ludwigii genome.

CONCLUSIONS

This work provides the first genome-wide picture of a S. ludwigii strain representing a step forward for a better understanding of the physiology and genetics of this species and of the Saccharomycodeacea family. The release of this genomic sequence and of the information extracted from it can contribute to guide the design of better wine preservation strategies to counteract spoilage prompted by S. ludwigii. It will also accelerate the exploration of this species as a cell factory, specially in production of fermented beverages where the use of Non-Saccharomyces species (including spoilage species) is booming.

From the vineyard to the cellar: new insights of Starmerella bacillaris (synonym Candida zemplinina) technological properties and genomic perspective

A large diversity of yeasts can be involved in alcoholic fermentation; however, Starmerella bacillaris strains have gained great attention due to their relevant and particular characteristics. S. bacillaris is commonly known as an osmotolerant, acidogenic, psychrotolerant, and fructophilic yeast. Most strains of this species are high producers of glycerol and show low ethanol production rates, being highlighted as promising alternatives to the manufacture of low-alcohol beverages. The increased production of high alcohols, such as benzyl alcohol that has antifungal and antibacterial properties, highlights S. bacillaris potential as a biocontrol agent. After harvest, antifungal yeasts become part of the must microbiota and may also improve the fermentation process. Moreover, during the fermentation, S. bacillaris releases important molecules with biotechnological properties, such as mannoproteins and glutathione. Considering the potential biotechnological properties of S. bacillaris strains, this review presents an overview of recent trends concerning the application of S. bacillaris in fermented beverages. KEY POINTS: •S. bacillaris as an alternative to the production of low-alcohol beverages. •S. bacillaris strains present biocontrol potential. •Molecules released by S. bacillaris may be of great biotechnological interest.

Biological Properties of Yeast-based Mannoprotein for Prospective Biomedical Applications

BACKGROUND

Natural products constitute more than half of all biomolecules lately being used in clinical settings. Mannoprotein derived from the yeast cell wall has found full biotechnological applications.

OBJECTIVE

This study was intended to investigate the antioxidant, anticancer, and toxicological properties of Kluyveromyces marxianus mannoprotein (KM).

METHODS

The KM extract was obtained through a sequence of operations, including centrifugation for cell isolation, precipitation with potassium citrate/sodium metabisulfite, and recovery and purification. Its antioxidant, growth inhibition, macrophage mitogenic, and toxic activities were evaluated for its future use in the biomedical field.

RESULTS

Significant inhibitory effects of KM were obtained on reactive species. It showed antiproliferative activity against HeLa (human cervical adenocarcinoma) and MCF-7 (human breast cancer) cell lines with no toxic effects on HUVECs (human umbilical vein endothelial cells). The in vitro model of CHO-K1 (Chinese hamster ovary) cell lines did not show the cytotoxic and genotoxic of KM. Moreover, it enhanced macrophage activity in terms of nitric oxide (NO) production and viability. No sign of acute toxicity was found in BALB/c mice, and body weight remained unchanged in guinea pigs over three months.

CONCLUSION

Comprehensive biological evaluations in this study are expected to expand the potential of KM as a natural material.

Mannoproteins from inactivated whole cells of baker's and brewer's yeasts as functional food ingredients: Isolation and optimization

Because of the structural multiplicity of yeast mannoproteins, they have shown a great interest as food ingredients for a wide range of applications. The yields and the structural properties of mannoproteins varied depending on the isolation methods and their sources (baker's and brewer's Saccharomyces cerevisiae yeasts). Noncovalently bound mannoproteins (6.5 kDa) with a mannan/protein ratio of 0.63 and 2.78 were recovered upon the heat treatment of brewer's and baker's yeasts, respectively, whereas sodium dodecyl sulfate treatment led mainly to the release of nonglycosylated proteins. The highest yield of mannoproteins was achieved upon the enzymatic isolation with Zymolyase^® from Arthrobacter luteus. The recovered covalently bound mannoproteins were characterized by a higher mannan/protein ratio (13.1 to 42.7) and a wider molecular weight distribution (5 to 10 kDa; 10 to 100 kDa; 100 to 400 kDa). Predictive models were developed to understand and modulate the effects of isolation parameters on yield, the mannoproteins content, and the mannan/protein ratio. The enzyme concentration was the most significant parameter affecting the yield, whereas the reaction time was the most significant parameter affecting mannan/protein ratio. Comparison of predicted and experimental values validated the established predicted models for the isolation of well-defined mannoproteins from yeast for targeted food applications. PRACTICAL APPLICATION: The increasing demand for clean label health-promoting foods has fueled the development of highly functional ingredients that offer both techno-functionalities and health-promoting properties. This study reveals the efficiency of whole inactivated yeasts as sources of mannoproteins. Given the dependence of the techno-functional and health-promoting properties of mannoproteins on their molecular properties, the investigation of the effects of the yeast sources and the type of isolation methods on the structural properties of mannoproteins would allow the modulation of their properties. Furthermore, the developed predictive models for the enzymatic process are expected to enhance the isolation efficiency of mannoproteins with well-defined structures.

Fate of Anthocyanins and Proanthocyanidins during the Alcoholic Fermentation of Thermovinified Red Musts by Different Saccharomyces cerevisiae Strains

UV-visible spectrophotometry, size exclusion chromatography, and UHPLC-QqQ-MS were combined to evaluate the respective impacts of chemical changes and adsorption by yeasts on both proanthocyanidins (PA) and anthocyanins during the fermentation of a thermovinified red must by four yeast strains. Results evidenced a sharp decrease in anthocyanins (∼45%) and color intensity (∼50%), along with the formation of pyranoanthocyanins and flavanol-anthocyanin dimers related to yeast metabolism. However, the latter only accounted for 10% of anthocyanin losses. Comparison of spectrophotometry and phloroglucinolysis data underlined the involvement of PAs in chemical changes, related to yeast metabolites but also to direct reactions. Color losses during fermentation in this case study were mostly related to the formation of colorless compounds and to a decrease of copigmentation. Adsorption represented only a small proportion of pigment losses (∼5%) but a major part of those corresponding to total oligomeric/polymeric species, which were specifically involved. Only small differences could be evidenced between the four studied strains.

Biobased Materials from Microbial Biomass and Its Derivatives

There is a strong public concern about plastic waste, which promotes the development of new biobased materials. The benefit of using microbial biomass for new developments is that it is a completely renewable source of polymers, which is not limited to climate conditions or may cause deforestation, as biopolymers come from vegetal biomass. The present review is focused on the use of microbial biomass and its derivatives as sources of biopolymers to form new materials. Yeast and fungal biomass are low-cost and abundant sources of biopolymers with high promising properties for the development of biodegradable materials, while milk and water kefir grains, composed by kefiran and dextran, respectively, produce films with very good optical and mechanical properties. The reasons for considering microbial cellulose as an attractive biobased material are the conformational structure and enhanced properties compared to plant cellulose. Kombucha tea, a probiotic fermented sparkling beverage, produces a floating membrane that has been identified as bacterial cellulose as a side stream during this fermentation. The results shown in this review demonstrated the good performance of microbial biomass to form new materials, with enhanced functional properties for different applications.

Influence of Saccharomyces and non-Saccharomyces Yeasts in the Formation of Pyranoanthocyanins and Polymeric Pigments during Red Wine Making

Yeast are able to modulate many sensory parameters of wines during red must fermentation. The effect on color and on the formation of derived pigments during fermentation has been studied thoroughly since the 90s. Yeast can increase grape anthocyanin’s color by acidification by hyperchromic effect (increase of flavylium molecules). Recent studies with non-Saccharomyces species, as Lachancea thermotolerans, described the intense effect of some strains on anthocyanin’s color, and subsequent, stability, by strongly reducing wine’s pH during fermentation. Moreover, selected yeast strains of Saccharomyces have been shown to release metabolites such as pyruvic acid or acetaldehyde that promote the formation of vitisin A and B pyranoanthocyanins during must fermentation. Schizosaccharomyces pombe, because of its specific metabolism, can produce higher concentrations of pyruvate, which enhances the formation of vitisin A-type derivatives. The hydroxycinnamate decarboxylase activity that some Saccharomyces strains express during fermentation also promotes the formation of vinylphenolic derivatives. Some non-Saccharomyces species, such as S. pombe or P. guilliermondii can also improve the production of these derivatives compared to selected strains of Saccharomyces cerevisiae. Lastly, some yeasts are also able to modulate the formations of polymeric pigments between grape anthocyanins and flavonoids, such as catechins and procyanidins.

Development of Potential Yeast Protein Extracts for Red Wine Clarification and Stabilization

Recently, new technologies have been combined to improve quality and sensorial diversity of wine. Several fining agents were developed to induce flocculation and sedimentation of particulate matter in wine, enhancing its clarification, and stabilization. The fining agents most commonly used are animal proteins, such as milk casein or egg albumin. However, its use is being related to food intolerance. To overcome this issue, alternative sources should be explored for use in industrial processes. In previous studies performed by our consortium, the potential of yeast protein extracts (YPE) in white wine clarification, stabilization, and curative processes was identified. Thus, the main objective of the present work is to select YPE with the potential to develop fining agents for red wine, without health risk to consumers. Therefore, five yeast strains were selected from a diversified collection of oenological yeasts, in order to produce protein extracts. Along with the fining trials, a vinification assay was performed to evaluate the maceration effect of the obtained YPE. The previously selected yeast strains were also screened for the production of the usual enzymatic activities found in commercial maceration preparations, namely polygalacturonase, cellulase, protease, and ß-glucosidase activities, in order to evaluate its potential effect on wine. Our results indicate that YPE, particularly BCVII 1, BCVII 2, and BCVII 5 were able to promote a significant brilliance increase, along with a turbidity reduction and final color improvement. In the vinification assay, BCVII 2 stands out with better results for color intensity and phenolic compounds content improvement. In what refers to enzymatic activities, BCVII 2 shows advantage over the other YPEs, due to its protease and β-glucosidase activity. We demonstrate that the selected YPEs, with emphasis on BCVII 2, may represent an efficient alternative to the commonly used fining products.

Characterization of the composition and the techno-functional properties of mannoproteins from Saccharomyces cerevisiae yeast cell walls

Broad molecular weight (MW) distribution and variability of mannan to protein ratio of purified mannoproteins (MP), isolated from yeast cell walls upon the enzymatic treatment, revealed their multiplicity. The main fraction of high-MW Agrimos®-MP1 and YCW-b-MP1' contained mannoproteins with a mannan to protein ratio of 3.5 and 6.9, respectively. Low-MW YCW-b-MP2' was mainly comprised of mannan, with a ratio of 181, whereas low-MW Agrimos®-MP2 was characterized by a ratio of 12.2. The solubility of MP1/MP2 was higher than that of MP1'/MP2'. Mannoproteins showed similar or lower solubility than mannan, and they exhibited a Newtonian behaviour. Sonication was the appropriate method for the formation of mannoproteins-based emulsions. Contrary to MP1/MP1'-based emulsions, MP2/MP2'-based ones showed higher affinity towards soybean oil than glyceryl-trioleate. pH affected the emulsifying ability of MP1/MP1'. MP1/MP1' showed similar or slightly inferior emulsifying properties than lecithin. This study is expected to broaden the applications of mannoproteins as value-added ingredients.

A simple and reliable method for the quantitative evaluation of anthocyanin adsorption by wine yeasts

Yeast pigments adsorption can modify wine color intensity and is considered an important trait in wine yeasts. The existing methods for the evaluation of yeast adsorption are laborious, time consuming, need confirmation experiments, or are difficult to apply for a large number of strains generated in breeding programs. In this study, a new test is proposed to measure yeast pigments adsorption and wine color in a single experiment. The optimized method included the microfermentation of grape musts obtained by thermal extraction, digital determination of yeast biomass color, and spectrophotometric wine intensity evaluation. Results showed significant negative correlation between yeast pigments adsorption and wine color intensity. Pigments adsorption occurs from the middle to the end of fermentation, indicating cell wall changes and/or anthocyanins modifications over the process. Significant differences were observed on anthocyanins adsorption and wine intensity among yeast strains independent of the grape variety, and yeasts could be grouped as low, medium and high adsorption strains. The proposed method showed high reproducibility and allows the concomitant screening of hundreds of yeast strains in a short period of time.

A Novel Method for the Quantification of White Wine Mannoproteins by a Competitive Indirect Enzyme-Linked Lectin Sorbent Assay (CI-ELLSA)

Mannoproteins (MPs) are cell wall proteoglycans released in wine by yeast during fermentation and ageing on lees, a procedure used for the production of several wines to enrich them in these components with consequences from both a technological and sensory point of view. Given the significance that wine MPs have for wine quality, winemakers would welcome a simple and accurate method for their quantification, as this would allow them to have a better control of this aspect at different winemaking stages. This study develops and validates a novel, simple and accurate method for MPs quantification in white wines based on a competitive indirect enzyme-linked lectin sorbent assay (CI-ELLSA), using the highly mannosylated yeast invertase as the standard. The method utilizes the lectin concanavalin A (ConA) as the immobilized ligand for MPs, and peroxidase, an enzyme rich in mannose, as the competitor for ConA. After addition of the peroxidase substrate, the intensity of the signal produced by the activity of this enzyme (absorbance at 450 nm) is inversely proportional to the amount of mannosylated proteins in the sample. Results have been validated on several wine styles including still, sparkling and sweet wines.

Polysaccharides, oligosaccharides and nitrogenous compounds change during the ageing of Tempranillo and Verdejo sparkling wines

BACKGROUND

Verdejo and Tempranillo are traditional varieties for producing still wines; however, they could provide an alternative for the manufacturing of sparkling wines. Sparkling wines were elaborated by the traditional method, followed by ageing on lees for 9 months. A study on the changes that take place in polysaccharides, oligosaccharides and nitrogenous compounds during the ageing on lees of Tempranillo and Verdejo sparkling wines has been undertaken.

RESULTS

Mannoproteins and the glucose residue of oligosaccharides were the major carbohydrates detected in all vinification stages. Yeast polysaccharides and glucan-like structures of the oligosaccharides increased after 3 months of ageing. The evolution of yeast polysaccharides and the composition of PRAG-like structure were different among grape varieties. A decrease in amino acids and biogenic amines was observed during the ageing. The contents of polysaccharides, oligosaccharides and nitrogenous compound were significantly higher in Tempranillo than in Verdejo sparkling wines at the end of the ageing period.

CONCLUSION

Polysaccharides and oligosaccharides from yeast were more significant autolysis markers of sparkling wines than the nitrogenous compounds. Our data suggest a potential cultivar effect on the evolution of yeast polysaccharides and on the composition of PRAG, which may influence the physico-chemical and sensory properties of sparkling wines. © 2017 Society of Chemical Industry.

Alcohol, Tannins, and Mannoprotein and their Interactions Influence the Sensory Properties of Selected Commercial Merlot Wines: A Preliminary Study

The objective of this study was to assess the influence of the interaction among alcohol, tannins, and mannoproteins on the aroma, flavor, taste, and mouthfeel characteristics of selected commercial Merlot wines. Merlot wines (n = 61) were characterized for wine chemistry parameters, including pH, titratable acidity, alcohol, glucose, fructose, tannin profile, total proteins, and mannoprotein content. Agglomerative clustering of these physicochemical characteristics revealed 6 groups of wines. Two wines were selected from each group (n = 12) and profiled by a trained sensory evaluation panel. One wine from each group was evaluated using the electronic tongue (e-tongue). Sensory evaluation results showed complex effects among tannins, alcohol, and mannoproteins on the perception of most aromas, flavors, tastes, and mouthfeel attributes (P < 0.05). The e-tongue showed distinct differences among the taste attributes of the 6 groups of wines as indicated by a high discrimination index (DI = 95). Strong correlations (r(2) > 0.930) were reported between the e-tongue and sensory perception of sweet, sour, bitter, burning, astringent, and metallic. This study showed that interactions among wine matrix components influence the resulting sensory perceptions. The strong correlation between the e-tongue and trained panel evaluations indicated the e-tongue can complement sensory evaluations to improve wine quality assessment.

Production of Volatile and Sulfur Compounds by 10 Saccharomyces cerevisiae Strains Inoculated in Trebbiano Must

In wines, the presence of sulfur compounds is the resulting of several contributions among which yeast metabolism. The characterization of the starter Saccharomyces cerevisiae needs to be performed also taking into account this ability even if evaluated together with the overall metabolic profile. In this perspective, principal aim of this experimental research was the evaluation of the volatile profiles, throughout GC/MS technique coupled with solid phase micro extraction, of wines obtained throughout the fermentation of 10 strains of S. cerevisiae. In addition, the production of sulfur compounds was further evaluated by using a gas-chromatograph coupled with a Flame Photometric Detector. Specifically, the 10 strains were inoculated in Trebbiano musts and the fermentations were monitored for 19 days. In the produced wines, volatile and sulfur compounds as well as amino acid concentrations were investigated. Also the physico-chemical characteristics of the wines and their electronic nose profiles were evaluated.

Sedaxicenes: potential new antifungal ferrocene-based agents?

Novel bifunctional organometallic antifungal agents has been designed from an active organic core and added with a metallocene moiety. Their synthesis and promising mycotoxicity has been presented.

Hyperproduction of β-Glucanase Exg1 Promotes the Bioconversion of Mogrosides in Saccharomyces cerevisiae Mutants Defective in Mannoprotein Deposition

Bacteria and fungi can secrete extracellular enzymes to convert macromolecules into smaller units. Hyperproduction of extracellular enzymes is often associated with alterations in cell wall structure in fungi. Recently, we identified that Saccharomyces cerevisiae kre6Δ mutants can efficiently convert mogroside V into mogroside III E, which has antidiabetic properties. However, the underlying efficient bioconversion mechanism is unclear. In the present study, the mogroside (MG) bioconversion properties of several cell wall structure defective mutants were analyzed. We also compared the cell walls of these mutants by transmission electron microscopy, a zymolyase sensitivity test, and a mannoprotein release assay. We found zymolyase-sensitive mutants (including kre1Δ, las21Δ, gas1Δ, and kre6Δ), with defects in mannoprotein deposition, exhibit efficient MG conversion and excessive leakage of Exg1; such defects were not observed in wild-type cells, or mutants with abnormal levels of glucans in the cell wall. Thus, yeast mutants defective in mannoprotein deposition may be employed to convert glycosylated bioactive compounds.

An evaluation study of different methods for the production of β-D-glucan from yeast biomass

β-Glucan is a proven beneficial and valuable molecule for human and animal health systems. It can be incorporated as an ingredient in various functional foods and beverages. β-Glucan has been isolated from various biological sources, fungi, mushrooms, algae, plants, and bacteria. The yeast cell wall comprises a suitable target for the extraction and purification of β-glucan. Although there are various extraction techniques, significant differences are observed as the technique used affects the final yield and purity, molecular weight, biological activity, solubility, quality, and other biological and functional properties of the extracted β-glucan. The aim of this review is the evaluation of different extraction methods for the production of β-glucan from yeast biomass. Furthermore, the use of industrial spent yeast waste from breweries and the wine industry for biotechnological β-glucan production and the concept of green wineries and breweries are discussed.

Accumulation and metabolism of selenium by yeast cells

This paper examines the process of selenium bioaccumulation and selenium metabolism in yeast cells. Yeast cells can bind elements in ionic from the environment and permanently integrate them into their cellular structure. Up to now, Saccharomyces cerevisiae, Candida utilis, and Yarrowia lipolytica yeasts have been used primarily in biotechnological studies to evaluate binding of minerals. Yeast cells are able to bind selenium in the form of both organic and inorganic compounds. The process of bioaccumulation of selenium by microorganisms occurs through two mechanisms: extracellular binding by ligands of membrane assembly and intracellular accumulation associated with the transport of ions across the cytoplasmic membrane into the cell interior. During intracellular metabolism of selenium, oxidation, reduction, methylation, and selenoprotein synthesis processes are involved, as exemplified by detoxification processes that allow yeasts to survive under culture conditions involving the elevated selenium concentrations which were observed. Selenium yeasts represent probably the best absorbed form of this element. In turn, in terms of wide application, the inclusion of yeast with accumulated selenium may aid in lessening selenium deficiency in a diet.

Unveiling the potential of novel yeast protein extracts in white wines clarification and stabilization

Fining agents derived from animal and mineral sources are widely used to clarify and stabilize white wines. Nevertheless, health and environmental problems are being raised, concerning the allergenic and environmental impact of some of those fining products. In this study, our aim is to validate the potential of yeast protein extracts, obtained from an alternative and safe source, naturally present in wine: oenological yeasts. Three untreated white wines were used in this work in order to evaluate the impact of these novel yeast protein extracts (YPE) in terms of the wine clarification and stabilization improvement. Two separated fining trials were thus conducted at laboratory scale and the yeast alternatives were compared with reference fining agents, obtained from mineral, animal and vegetable origins. Our results indicate that YPE were capable to promote (i) brilliance/color improvement, (ii) turbidity reduction (76–89% comparing with the untreated wines), and (iii) production of compact and homogeneous lees (44% smaller volume than obtained with bentonite). Additionally, after submitting wines to natural and forced oxidations, YPE treatments revealed (iv) different forms of colloidal stabilization, by presenting comparable or superior effects when particularly compared to casein. Altogether, this study reveals that YPE represent a promising alternative for white wine fining, since they are resultant from a natural and more sustainable origin, at present not regarded as potential allergenic according to Regulation (EC) No. 1169/2011.

L-histidine inhibits biofilm formation and FLO11-associated phenotypes in Saccharomyces cerevisiae flor yeasts

Flor yeasts of Saccharomyces cerevisiae have an innate diversity of Flo11p which codes for a highly hydrophobic and anionic cell-wall glycoprotein with a fundamental role in biofilm formation. In this study, 380 nitrogen compounds were administered to three S. cerevisiae flor strains handling Flo11p alleles with different expression levels. S. cerevisiae strain S288c was used as the reference strain as it cannot produce Flo11p. The flor strains generally metabolized amino acids and dipeptides as the sole nitrogen source, although with some exceptions regarding L-histidine and histidine containing dipeptides. L-histidine completely inhibited growth and its effect on viability was inversely related to Flo11p expression. Accordingly, L-histidine did not affect the viability of the Δflo11 and S288c strains. Also, L-histidine dramatically decreased air-liquid biofilm formation and adhesion to polystyrene of the flor yeasts with no effect on the transcription level of the Flo11p gene. Moreover, L-histidine modified the chitin and glycans content on the cell-wall of flor yeasts. These findings reveal a novel biological activity of L-histidine in controlling the multicellular behavior of yeasts [corrected].

Metabolic and transcriptomic response of the wine yeast Saccharomyces cerevisiae strain EC1118 after an oxygen impulse under carbon-sufficient, nitrogen-limited fermentative conditions

During alcoholic fermentation, Saccharomyces cerevisiae is exposed to continuously changing environmental conditions, such as decreasing sugar and increasing ethanol concentrations. Oxygen, a critical nutrient to avoid stuck and sluggish fermentations, is only discretely available throughout the process after pump-over operation. In this work, we studied the physiological response of the wine yeast S. cerevisiae strain EC1118 to a sudden increase in dissolved oxygen, simulating pump-over operation. With this aim, an impulse of dissolved oxygen was added to carbon-sufficient, nitrogen-limited anaerobic continuous cultures. Results showed that genes related to mitochondrial respiration, ergosterol biosynthesis, and oxidative stress, among other metabolic pathways, were induced after the oxygen impulse. On the other hand, mannoprotein coding genes were repressed. The changes in the expression of these genes are coordinated responses that share common elements at the level of transcriptional regulation. Beneficial and detrimental effects of these physiological processes on wine quality highlight the dual role of oxygen in 'making or breaking wines'. These findings will facilitate the development of oxygen addition strategies to optimize yeast performance in industrial fermentations.

Changes in polysaccharide composition during sparkling wine making and aging

The evolution in polysaccharide composition and molecular weights during sparkling wine making and aging was studied for the first time in this work. Different autochthonous grape varieties from Spain (Verdejo, Viura, Malvası́a, Albarı́n, Godello, Garnacha and Prieto Picudo) were used to elaborate sparkling wines following the champenoise method. Principal component analysis showed differentiation of wines according to polysaccharide families. This differentiation was due to the process of aging on yeast lees, but not to the variety employed. The content of mannoproteins during aging was positively correlated (r = 0.792) with total polysaccharides from grapes. After six months of aging the highest content of mannoproteins and polysaccharides rich in arabinose and galactose was obtained. Also a shift to lower molecular weights was observed. The combination of these two characteristics could imply a better foam stability and thus sensory quality of sparkling wines.

Use of atomic force microscopy (AFM) to explore cell wall properties and response to stress in the yeast Saccharomyces cerevisiae

Over the past 20 years, the yeast cell wall has been thoroughly investigated by genetic and biochemical methods, leading to remarkable advances in the understanding of its biogenesis and molecular architecture as well as to the mechanisms by which this organelle is remodeled in response to environmental stresses. Being a dynamic structure that constitutes the frontier between the cell interior and its immediate surroundings, imaging cell surface, measuring mechanical properties of cell wall or probing cell surface proteins for localization or interaction with external biomolecules are among the most burning questions that biologists wished to address in order to better understand the structure-function relationships of yeast cell wall in adhesion, flocculation, aggregation, biofilm formation, interaction with antifungal drugs or toxins, as well as response to environmental stresses, such as temperature changes, osmotic pressure, shearing stress, etc. The atomic force microscopy (AFM) is nowadays the most qualified and developed technique that offers the possibilities to address these questions since it allows working directly on living cells to explore and manipulate cell surface properties at nanometer resolution and to analyze cell wall proteins at the single molecule level. In this minireview, we will summarize the most recent contributions made by AFM in the analysis of the biomechanical and biochemical properties of the yeast cell wall and illustrate the power of this tool to unravel unexpected effects caused by environmental stresses and antifungal agents on the surface of living yeast cells.