Research Articles (Institute for Wine Biotechnology)
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- Item3-way networks : application of hypergraphs for modelling increased complexity in comparative genomics(PLoS, 2015-03) Weighill, Deborah A.; Jacobson, Daniel A.We present and develop the theory of 3-way networks, a type of hypergraph in which each edge models relationships between triplets of objects as opposed to pairs of objects as done by standard network models. We explore approaches of how to prune these 3-way networks, illustrate their utility in comparative genomics and demonstrate how they find relationships which would be missed by standard 2-way network models using a phylogenomic dataset of 211 bacterial genomes.
- ItemBioengineering beans for phosphate-deficient soils in southern Africa(Academy of Science for South Africa, 2003) Viktor, A.; Cordero-Otero, R.; Valentine, A.APPROXIMATELY EIGHT SPECIES OF SOUTHern African legumes are currently used as sustainable food crops. Biotechnology has the potential to improve the productivity of growing these plants by small-scale farmers who cannot afford sufficient phosphate fertilizer to optimize their nitrogen fixation and hence conversion to edible protein. The metabolic adaptations that enable legumes to fix atmospheric nitrogen are currently being investigated by our group for the purpose of genetic modification to enhance crop yields. Until now, attempts at modifying host plants or symbiotic bacteria have not significantly enhanced N2 fixation. We propose, instead, to bioengineer the key enzymes that control the mechanisms involved in protein formation. This may lead to enhanced seed protein content, which would be of advantage to poor communities that rely on this source of food. We postulate that misregulation of phosphoenolpyruvate carboxylase (PEPc) could be exploited by biotechnology to improve N2 fixation and protein content. We have found that, as distinct from their roots, legume nodules are under permanent phosphate stress, even during optimal phosphate supply to the host plant, implying that the development of phosphate stress may engage different forms of PEPc to ensure continued nodule functioning.
- ItemBiogenic amines in wine : understanding the headache(SASEV, 2008-09) Smit, A. Y.; Du Toit, W. J.; Du Toit, M.The presence of biogenic amines in wine is becoming increasingly important to consumers and producers alike, due to the potential threats of toxicity to humans and consequent trade implications. In the scientific field, biogenic amines have the potential to be applied as indicators of food spoilage and/or authenticity. Biogenic amines can be formed from their respective amino acid precursors by various microorganisms present in the wine, at any stage of production, ageing or storage. To understand the large number of factors that could influence the formation of biogenic amines, the chemical, biochemical, enzymatic and genetic properties relating to these compounds have to be considered. Analytical and molecular methods to detect biogenic amines in wine, as well as possibilities that could enable better control over their production levels in wine will also be explored in this review.
- ItemBiosynthesis of levan, a bacterial extracellular polysaccharide, in the yeast Saccharomyces cerevisiae(PLoS, 2013) Franken, Jaco; Brandt, Bianca A.; Tai, Siew L.; Bauer, FlorianLevans are fructose polymers synthesized by a broad range of micro-organisms and a limited number of plant species as non-structural storage carbohydrates. In microbes, these polymers contribute to the formation of the extracellular polysaccharide (EPS) matrix and play a role in microbial biofilm formation. Levans belong to a larger group of commercially important polymers, referred to as fructans, which are used as a source of prebiotic fibre. For levan, specifically, this market remains untapped, since no viable production strategy has been established. Synthesis of levan is catalysed by a group of enzymes, referred to as levansucrases, using sucrose as substrate. Heterologous expression of levansucrases has been notoriously difficult to achieve in Saccharomyces cerevisiae. As a strategy, this study used an invertase (Δsuc2) null mutant and two separate, engineered, sucrose accumulating yeast strains as hosts for the expression of the levansucrase M1FT, previously cloned from Leuconostoc mesenteroides. Intracellular sucrose accumulation was achieved either by expression of a sucrose synthase (Susy) from potato or the spinach sucrose transporter (SUT). The data indicate that in both Δsuc2 and the sucrose accumulating strains, the M1FT was able to catalyse fructose polymerisation. In the absence of the predicted M1FT secretion signal, intracellular levan accumulation was significantly enhanced for both sucrose accumulation strains, when grown on minimal media. Interestingly, co-expression of M1FT and SUT resulted in hyper-production and extracellular build-up of levan when grown in rich medium containing sucrose. This study presents the first report of levan production in S. cerevisiae and opens potential avenues for the production of levan using this well established industrial microbe. Furthermore, the work provides interesting perspectives when considering the heterologous expression of sugar polymerizing enzymes in yeast.
- ItemCarnitine requires choline to exert physiological effects in saccharomyces cerevisiae(Frontiers Media, 2018-07-02) Du Plessis, Michelle; Franken, Jaco; Bauer, Florian; De Biase, DanielaL-Carnitine is a key metabolite in the energy metabolism of eukaryotic cells, functioning as a shuttling molecule for activated acyl-residues between cellular compartments. In higher eukaryotes this function is essential, and defects in carnitine metabolism has severe effects on fatty acid and carbon metabolism. Carnitine supplementation has been associated with an array of mostly beneficial impacts in higher eukaryotic cells, including stress protection and regulation of redox metabolism in diseased cells. Some of these phenotypes have no obvious link to the carnitine shuttle, and suggest that carnitine has as yet unknown shuttle-independent functions. The existence of shuttle-independent functions has also been suggested in Saccharomyces cerevisiae, including a beneficial effect during hydrogen peroxide stress and a detrimental impact when carnitine is co-supplemented with the reducing agent dithiothreitol (DTT). Here we used these two distinct yeast phenotypes to screen for potential genetic factors that suppress the shuttle independent physiological effects of carnitine. Two deletion strains, Δcho2 and Δopi3, coding for enzymes that catalyze the sequential conversion of phosphatidylethanolamine to phosphatidylcholine were identified for suppressing the phenotypic effects of carnitine. Additional characterisation indicated that the suppression cannot be explained by differences in phospholipid homeostasis. The phenotypes could be reinstated by addition of extracellular choline, but show that the requirement for choline is not based on some overlapping function or the structural similarities of the two molecules. This is the first study to suggest a molecular link between a specific metabolite and carnitine-dependent, but shuttle-independent phenotypes in eukaryotes.
- ItemCharacterisation of non-saccharomyces yeasts using different methodologies and evaluation of their compatibility with malolactic fermentation(South African Society for Enology and Viticulture, 2017) Du Plessis, H. W.; Du Toit, M.; Hoff, J. W.; Hart, R. S.; Ndimba, B. K.; Jolly, N. P.Although Saccharomyces cerevisiae is the yeast species predominantly used for alcoholic fermentation, non-Saccharomyces yeast species are also important because they produce secondary metabolites that can contribute to the final flavour and taste of wines. In this study, 37 strains representing seven non-Saccharomyces species were characterised and evaluated for potential use in wine production, as well as for their effects on malolactic fermentation (MLF). Contour-clamped homogeneous electric field (CHEF) gel electrophoresis and matrix-assisted laser desorption ionisation using a time-of-flight mass spectrometer (MALDI-TOF MS) were used to verify species identity and to determine intra-species variation. Extracellular enzyme production, malic acid degradation and the fermentation kinetics of the yeasts were also investigated. CHEF karyotyping and MALDI-TOF MS were useful for identifying and typing Hanseniaspora uvarum, Lachancea thermotolerans, Candida zemplinina (synonym: Starmerella bacillaris) and Torulaspora delbrueckii strains. Only H. uvarum and Metschnikowia pulcherrima strains were found to have β-glucosidase activity. M. pulcherrima strains also had protease activity. Most of the strains showed limited malic acid degradation, and only Schizosaccharomyces pombe and the C. zemplinina strains showed mentionable degradation. In synthetic wine fermentations, C. stellata, C. zemplinina, H. uvarum, M. pulcherrima and Sc. pombe strains were shown to be slow to medium fermenters, whereas L. thermotolerans and T. delbrueckii strains were found to be medium to strong fermenters. The effect of the yeasts on MLF varied, but inhibition was strain dependent.
- ItemCharacterization of the Viable but Nonculturable (VBNC) State in Saccharomyces cerevisiae(Public Library of Science, 2013-10-29) Salma, Mohammad; Rousseaux, Sandrine; Sequeira-Le Grand, Anabelle; Divol, Benoit; Alexandre, HerveThe Viable But Non Culturable (VBNC) state has been thoroughly studied in bacteria. In contrast, it has received much less attention in other microorganisms. However, it has been suggested that various yeast species occurring in wine may enter in VBNC following sulfite stress.In order to provide conclusive evidences for the existence of a VBNC state in yeast, the ability of Saccharomyces cerevisiae to enter into a VBNC state by applying sulfite stress was investigated. Viable populations were monitored by flow cytometry while culturable populations were followed by plating on culture medium. Twenty-four hours after the application of the stress, the comparison between the culturable population and the viable population demonstrated the presence of viable cells that were non culturable. In addition, removal of the stress by increasing the pH of the medium at different time intervals into the VBNC state allowed the VBNC S. cerevisiae cells to “resuscitate”. The similarity between the cell cycle profiles of VBNC cells and cells exiting the VBNC state together with the generation rate of cells exiting VBNC state demonstrated the absence of cellular multiplication during the exit from the VBNC state. This provides evidence of a true VBNC state. To get further insight into the molecular mechanism pertaining to the VBNC state, we studied the involvement of the SSU1 gene, encoding a sulfite pump in S. cerevisiae. The physiological behavior of wild-type S. cerevisiae was compared to those of a recombinant strain overexpressing SSU1 and null Δssu1 mutant. Our results demonstrated that the SSU1 gene is only implicated in the first stages of sulfite resistance but not per se in the VBNC phenotype. Our study clearly demonstrated the existence of an SO2-induced VBNC state in S. cerevisiae and that the stress removal allows the “resuscitation” of VBNC cells during the VBNC state.
- ItemDeconstructing wine grape cell walls with enzymes during winemaking : new insights from glycan microarray technology(MDPI, 2019-01-04) Gao, Yu; Zietsman, Anscha J. J.; Vivier, Melane A.; Moore, John P.Enzyme-aid maceration is carried out in most modern winemaking industries with a range of positive impacts on wine production. However, inconsistencies in enzyme efficiency are an issue complicated by unclear targets (limited information available on berry cell wall architecture of different cultivars) and the complex wine environment (i.e., fermenting must). Recent studies have been performed to develop a clearer picture of grape cell wall structures, maceration effects, and interactions between important wine compounds and grape-derived polysaccharides. This review highlights critically important recent studies on grape berry cell wall changes during ripening, the importance of enzymes during maceration (skin contact phase) and deconstruction processes that occur during alcoholic fermentation. The novelty of the Comprehensive Microarray Polymer Profiling (CoMPP) technique using cell wall probes (e.g., antibodies) as a method for following cell wall derived polymers during different biological and biotechnological processes is discussed. Recent studies, using CoMPP together with classical analytical methods, confirmed the developmental pattern of berry cell wall changes (at the polymer level) during grape ripening. This innovative technique were also used to track enzyme-assisted depectination of grape skins during wine fermentation and determine how this influence the release of wine favourable compounds. Furthermore, polysaccharides (e.g., arabinogalactan proteins) present in the final wine could be identified. Overall, CoMPP provides a much more enriched series of datasets compared to traditional approaches. Novel insights and future studies investigating grape cell wall and polyphenol interactions, and the tailoring of enzyme cocktails for consistent, effective and “customized” winemaking is advanced and discussed.
- ItemDetermining the impact of industrial wine yeast strains on organic acid production under white and red wine-like fermentation conditions(South African Society for Enology and Viticulture, 2015) Chidi, B. S.; Rossouw, D.; Buica, A. S.; Bauer, FlorianOrganic acids are a major contributor to wine flavour and aroma. In the past, the scientific focus has mostly been on organic acids derived from grapes or on the transformation of malic acid to lactic acid by lactic acid bacteria, since these acids contribute significantly to the final total acidity of wine. However, the organic acid concentration and composition also change significantly during alcoholic fermentation, yet only limited information regarding the impact of different yeast strains on these changes has been published. Here we report on changes in organic acid (malic, tartaric, citric, succinic, acetic and pyruvic) composition during fermentation by five widely used industrial wine yeast strains in a synthetic grape must (MS300) reflecting two very different, but both wine-like, fermentation conditions. Samples were obtained from three physiological stages during fermentation, namely the exponential growth phase (day 2), early stationary phase (day 5) and late stationary phase (day 14). These different stages were selected to provide more information on acid evolution throughout fermentation, as well as on the impact of nutritional and environmental conditions during aerobic and anaerobic fermentation. Among other observations, some strains (such as VIN13 and 285) were shown to be generally higher producers of most acids in white and/ or red wine fermentation settings, while other strains (such as DV10) were generally lower acid producers. The data clearly demonstrate that different strains have different acid consumption and production patterns, and this presents a first step towards enabling winemakers to appropriately select strains for acid management during fermentation.
- ItemThe diversity and dynamics of indigenous yeast communities in grape must from vineyards employing different agronomic practices and their influence on wine fermentation(South African Society for Enology and Viticulture, 2015) Bagheri, Bahareh; Bauer, Florian; Setati, M. E.The current study evaluated the diversity of yeast species in Cabernet Sauvignon grape must derived from three neighbouring vineyards from a similar terroir but on which significantly different management practices are employed. The fermentation kinetics and yeast population dynamics were monitored from the beginning to the end of spontaneous fermentation. The grape musts were characterised by distinct yeast populations comprising oxidative, weakly fermentative and strongly fermentative yeasts. Different combinations of dominant non-Saccharomyces yeasts were observed in each must, with significantly different assortments of dominant species, including Starmerella bacillaris (synonym Candida zemplinina), Lachancea thermotolerans, Hanseniaspora uvarum, Candida parapsilosis and Wickerhamomyces anomalus. None of these yeast consortia appeared to affect the growth of Saccharomyces cerevisiae or inhibit the overall progress of fermentation. However, the percentage of fermentative yeasts was positively correlated with the fermentation rate. Glucose and fructose consumption rates suggested active participation of both glucophilic and fructophilic yeasts from the onset of fermentation. The data highlight two parameters, viz. initial cell concentration and yeast community composition, as important fermentation drivers and open the possibility to predict fermentation behaviour based on the initial composition of the yeast community.
- ItemEffect of different extraction methods on the quality and biochemical attributes of pomegranate juice and the application of Fourier transformed infrared spectroscopy in discriminating between different extraction methods(Frontiers Media, 2021-08-23) Arendse, Ebrahiema; Nieuwoudt, Helene; Fawole, Olaniyi Amos; Linus Opara, UmezuruikeThis study investigated the effects of extraction methods on the physicochemical, phytochemical, and antioxidant properties of pomegranate juice (cv. Wonderful). In addition, the application of attenuated total reflectance Fourier transformed mid-infrared (ATR-FT-MIR) spectroscopy and chemometrics were explored in order to discriminate between different extraction methods. Juice variants evaluated included juice extracted without crushing the seeds (arils only) using a juice extractor (JE), juice extracted by crushing the seeds using a blender (arils plus seed) (JB), and juice extracted from half fruit using a commercial hand press juicer (CH). Juice extracted from CH had higher total soluble solid (TSS) content (18.20%), TSS/TA ratio (15.83), and color properties (a* = 32.67, b* = 11.80, C* = 34.77) compared with extraction methods JE and JB. The juice extracted from JB showed the highest titratable acidity (2.17%), cloudiness (0.43), and lowest pH value (2.69). The total phenolics and anthocyanin content in the investigated juice ranged from 1.87 to 3.04 g gallic acid equivalent (GAE)/L and 37.74–43.67 mg cyanidin 3-glucoside equivalent/L of crude juice, respectively. Juice extracted from JB and CH was significantly higher in phenolic and anthocyanin compared with JE. Orthogonal partial least squares discriminant analysis (OPLS-DA) and principal component analysis (PCA) were used for classification. Classification accuracy of 100% was achieved between the three methods. The S-line plot revealed that the corresponding wavelength bands within the following regions 1,090, 1,250, 1,750, and 3,200 cm−1 were responsible for discrimination between the different extraction methods. Our results suggest that the main contributor to the discrimination between extraction methods were TSS, TSS/TA, color attributes, and anthocyanin content. Overall, this study has demonstrated that ATR-FT-MIR spectroscopy provides a powerful way to discriminate between juice extraction methods.
- ItemEnzymes in winemaking : harnessing natural catalysts for efficient biotransformations(South African Society for Enology and Viticulture, 2000) Van Rensburg, P.; Pretorius, I. S.Enzymes play a definitive role in the ancient and complex process of winemaking. From a scientific and technical point of view, wine can be seen as the product of enzymatic transformation of grape juice. From the pre-fermentation stage, through fermentation, post-fermentation and aging, enzymes are the major driving forces catalysing various biotransformation reactions. These biocatalysts originate not only from the grape itself but also from yeasts and other microbes (fungi and bacteria) associated with vineyards and wine cellars. Through better understanding of these enzymatic activities, winemakers have come to learn how to control the unwanted enzymes while optimising the desired activities. Today, winemakers reinforce and extend the action of these endogenous enzymes by the judicious application of an ever-increasing spectrum of commercial enzyme preparations. These enzyme preparations are applied to winemaking with the aims of improving the clarification and processing of wine, releasing varietal aromas from precursor compounds, reducing ethyl carbamate formation and lowering alcohol levels. This review article summarises the most important enzymes applied to winemaking, the nature and structure of their substrates, and the reactions catalysed by these enzymes. This paper also reviews the limitations of the endogenous enzymes derived from grapes and microbes present in must and wine, along with the effects of commercial enzyme preparations on process technology and the quality of the final product. Prospects of developing wine yeast strains expressing tailored enzymes are also highlighted.
- ItemFermentation-derived aroma compounds in varietal young wines from South Africa(SASEV, 2010-09) Louw, L.; Tredoux, A. G. J.; Van Rensburg, P.; Kidd, M.; Naes, T.; Nieuwoudt, HeleneThe volatile composition of 925 single cultivar young Sauvignon blanc, Chardonnay, Pinotage, Merlot, Shiraz and Cabernet Sauvignon wines of vintages 2005 to 2007, was determined using gas chromatography-flame ionisation detection. Compositional data were compared to published data on young wines from South Africa and other countries. South African young wines analysed in this study had a largely similar volatile composition to that reported in the literature. Significant between-vintage and between-cultivar differences were observed in the volatile composition of the wines investigated in this study. The concentration ranges of four compounds in red wines, hexanol, propanol, diethyl succinate and ethyl lactate, and four compounds in white wines, 2-phenylethanol, hexanoic acid, isoamyl acetate and propanol, were not influenced by vintage effects. This finding was interpreted as the first indication that typical concentration ranges for some aroma compounds can be established for South African young cultivar wines. A trend was observed in the white wines that the alcohols and their respective acetate esters, as well as fatty acids and their ethyl esters, were responsible for the vintage-related effects. Differences in volatile composition between Chardonnay and Sauvignon blanc wines could also largely be explained on the same basis. Classification models were established to discriminate between individual red wine cultivars and between the two white wine cultivars and correct classification rates of respectively, 79 % and 85 % were achieved.
- ItemGenetic improvement of grapevine : tailoring grape varieties for the third millennium(South African Society of Enology and Viticulture, 2000) Vivier, M. A.; Pretorius, I. S.The remarkable propagative aptitute of grapevine is one of the key factors contributing to its success as a cultivated species and to the spread of the domesticated grapevine, establishing it as one of the most important fruit species worldwide. Today there are some 8 million hectares of vineyards across the world. It is therefore titting that the successful implementation of the powerful technology of gene manipulation in grapevine is to a large extent reliant on this regenerative ability. Currently, several varieties of grapevines have been successfully genetically transformed, largely by employing somatic embryogenesis to generate highly regenerative target material. Especially attractive in the wine industry is the possibility of improving grapevine varieties by the addition of genes that confer useful traits, such as resistances against biotic and abiotic factors and manipulation of certain metabolic functions. In principle, gene transfer technology allows for the directed manipulation of a specific trait without altering the characteristic nature of the cultivar, permitting the improvement of the traditional cultivars while maintaining their established varietal characteristics. For the most part, targeted traits currently include disease resistance and improved berry quality. The promise of this technology is threatened by worldwide resistance to genetically modified organisms, and in the wine industry by complications surrounding the property rights and naming of transgenic vines. If it is not possible to maintain the varietal name when a transgenic vine has the same properties as the original well known variety, the significant advantages of gene technology over traditional breeding programmes are to a large extent lost. If these and other complications can be overcome, the integration of this powerful technology with traditional breeding programmes, and with other initiatives such as the study of the grapevine genome, will ensure a new era in the cultivation of this ancient species.
- ItemDie genetiese verbetering van wyndruifkultivars en wyngisrasse vir 'n markgerigte wynbedryf : nuwe benaderings tot die oeroue kuns van wynbereiding(AOSIS OpenJournals, 2003) Pretorius, I. S.The widening gap between wine production and wine consumption, the shift of consumer preferences away from basic commodity wine to top quality wine, and the gruelling competition brought about by economic globalisation call for a total revolution in the magical world of wine. In the process of transforming the wine industry from a production-driven industry to a market-orientated enterprise, there is an increasing dependence on, amongst others, biotechnological innovation to launch the wine industry with a quantum leap across the formidable market challenges of the 21st century. Market-orientated designer grape cultivars and wine yeast strains are currently being genetically programmed with surgical precision for the cost-competitive production of high quality grapes and wine with relatively minimal resource inputs and a low environmental impact. With regard to Grapevine Biotechnology, this entails the establishment of stress tolerant and disease resistant varieties of Vitis vinifera with increased productivity, efficiency, sustainability and environmental friendliness, especially regarding improved pest and disease control, water use efficiency and grape quality. With regard to Wine Yeast Biotechnology, the emphasis is on the development of Saccharomyces cerevisiae strains with improved fermentation, processing and biopreservation abilities, and capacities for an increase in the wholesomeness and sensory quality of wine. The successful commercialisation of transgenic grape cultivars and wine yeasts depends on a number of scientific, technical, safety, ethical, legal, economic and marketing factors, and it therefore will be unwise to entertain high expectations in the short term. However, in the light of the phenomenal potential advantages of tailor-made grape varieties and yeast strains, it would be equally self-destructive in the long term if this strategically important “life insurance policy” is not taken out by the wine industry. This overview highlights the most important examples of the way in which V. vinifera grape varieties and S. cerevisiae wine yeast strains are currently being designed with surgical precision on the basis of market demand for the cost-effective, sustainable and environmentally friendly production of healthy, top quality grapes and wine.
- ItemThe grapevine and wine microbiome : insights from high-throughput amplicon sequencing(Frontiers Media, 2017) Morgan, Horatio H.; Du Toit, Maret; Setati, Mathabatha E.From the time when microbial activity in wine fermentation was first demonstrated, the microbial ecology of the vineyard, grape, and wine has been extensively investigated using culture-based methods. However, the last 2 decades have been characterized by an important change in the approaches used for microbial examination, due to the introduction of DNA-based community fingerprinting methods such as DGGE, SSCP, T-RFLP, and ARISA. These approaches allowed for the exploration of microbial community structures without the need to cultivate, and have been extensively applied to decipher the microbial populations associated with the grapevine as well as the microbial dynamics throughout grape berry ripening and wine fermentation. These techniques are well-established for the rapid more sensitive profiling of microbial communities; however, they often do not provide direct taxonomic information and possess limited ability to detect the presence of rare taxa and taxa with low abundance. Consequently, the past 5 years have seen an upsurge in the application of high-throughput sequencing methods for the in-depth assessment of the grapevine and wine microbiome. Although a relatively new approach in wine sciences, these methods reveal a considerably greater diversity than previously reported, and identified several species that had not yet been reported. The aim of the current review is to highlight the contribution of high-throughput next generation sequencing and metagenomics approaches to vineyard microbial ecology especially unraveling the influence of vineyard management practices on microbial diversity.
- ItemIdentifying genes that impact on aroma profiles produced by Saccharomyces cerevisiae and the production of higher alcohols(Springer-Verslag, 2011-05) Styger, Gustav; Jacobson, Dan; Bauer, FlorianDuring alcoholic fermentation, many volatile aroma compounds are formed by Saccharomyces cerevisiae, including esters, fatty acids, and higher alcohols. While the metabolic network that leads to the formation of these compounds is reasonably well mapped, surprisingly little is known about specific enzymes involved in specific reactions, the regulation of the network, and the physiological roles of individual pathways within the network. Furthermore, different yeast strains tend to produce significantly different aroma profiles. These differences are of tremendous biotechnological interest, since producers of alcoholic beverages such as wine and beer are searching for means to diversify and improve their product range. Various factors such as the redox, energy, and nutritional balance of a cell have previously been suggested to directly or indirectly affect and regulate the network. To gain a better understanding of the regulations and physiological role of this network, we screened a subset of the EUROSCARF strain deletion library for genes that, when deleted, would impact most significantly on the aroma profile produced under fermentative conditions. The 10 genes whose deletion impacted most significantly on higher alcohol production were selected and further characterized to assess their mode of action within or on this metabolic network. This is the first description of a large-scale screening approach using aroma production as the primary selection criteria, and the data suggest that many of the identified genes indeed play central and direct roles within the aroma production network of S. cerevisiae.
- ItemThe impact of carbohydrate-active enzymes on mediating cell wall polysaccharide-tannin interactions in a wine-like matrix(Elsevier, 2019-12-14) Osete-Alcaraz, Andrea; Gomez-Plaza, Encarna; Martinez-Perez, Pilar; Weiller, Florent; Schuckel, Julia; Willats, William G. T.; Moore, John P.; Ros-Garcia, Jose M.; Bautista-Ortin, Ana B.Tannins are present in grape skins and seeds from where they are transferred into the must-wine matrix during the maceration stages of winemaking. However, tannin transfer is often incomplete. This could be due, among other reasons, to tannins becoming bound to grape cell wall polysaccharides, including soluble polymers, which are released during vinification and are present in high concentrations in the must/wine. The use of cell wall deconstructing enzymes offers the possibility of reducing these interactions, releasing more tannins into the final wine. The main aim of this study was to evaluate the optimal addition (individually, in combination or sequentially) of hydrolytic enzymes that would prevent tight polysaccharide-tannin associations. The use of comprehensive microarray polymer profiling (CoMPP) methodology provided key insights into how the enzyme treatments impacted the grape cell wall matrix and tannin binding. The results demonstrated that poly-galacturonase + pectin-lyase promoted the highest release of tannins into solution.
- ItemImpact of grape temperature at pressing on organic acids and oenological characteristics of Méthode Cap Classique wines(South African Society for Enology and Viticulture, 2018) Chidi, B. S.; Mafata, M.; Notshokovu, N. Z.; Van Jaarsveld, F.Maintaining the chemical composition of a wine is essential for the wine industry. Although the sugar-acid balance of a wine is of primary sensory importance, individual acids and oenological parameters are equally important. The main focus of this study was to investigate the impact of grape temperature at harvest, on the oenological volatile acidity (VA), titratable acidity (TA), pH and alcohol levels and organic acid (citric, malic, pyruvic and succinic) characteristics of Méthode Cap Classique (MCC) wines during winemaking, produced from grape cultivars obtained from two regions. Chardonnay and Pinot noir grapes were obtained from Robertson (warmer) and Elgin (cooler) regions and were subjected to different temperature treatments, i.e. 0, 10, 25 and 30oC before further processing, including pressing, primary fermentation, blending, tirage, secondary fermentation, riddling and disgorging. Grape temperature was mostly responsible for a significantly higher pH of Robertson (0 and 10ºC) and lower pH (0ºC) of Elgin post-tirage wines. Chardonnay base wines from both regions that were vinified from grapes at lower temperatures (0 and 10oC) were richer in malic- and succinic acid, while Pinot noir wines from both regions were characterised by higher malic-, citric- and pyruvic acid. Pyruvic acid was only detected after the secondary fermentations in wines from both regions. To our knowledge, this study is the first to investigate the influence of grape temperature on the oenological and organic acid characteristics of MCC wines in different regions, and throughout different production stages.
- ItemThe impact of single amino acids on growth and volatile aroma production by Saccharomyces cerevisiae strains(Frontiers Media, 2017) Fairbairn, Samantha; McKinnon, Alexander; Musarurwa, Hannibal T.; Ferreira, Antonio C.; Bauer, Florian; Lanciotti, RosalbaNitrogen availability and utilization by Saccharomyces cerevisiae significantly influence fermentation kinetics and the production of volatile compounds important for wine aroma. Amino acids are the most important nitrogen source and have been classified based on how well they support growth. This study evaluated the effect of single amino acids on growth kinetics and major volatile production of two phenotypically different commercial wine yeast strains in synthetic grape must. Four growth parameters, lag phase, maximum growth rate, total biomass formation and time to complete fermentation were evaluated. In contrast with previous findings, in fermentative conditions, phenylalanine and valine supported growth well and asparagine supported it poorly. The four parameters showed good correlations for most amino acid treatments, with some notable exceptions. Single amino acid treatments resulted in the predictable production of aromatic compounds, with a linear correlation between amino acid concentration and the concentration of aromatic compounds that are directly derived from these amino acids. With the increased complexity of nitrogen sources, linear correlations were lost and aroma production became unpredictable. However, even in complex medium minor changes in amino acid concentration continued to directly impact the formation of aromatic compounds, suggesting that the relative concentration of individual amino acids remains a predictor of aromatic outputs, independently of the complexity of metabolic interactions between carbon and nitrogen metabolism and between amino acid degradation and utilization pathways.
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