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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.
- 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.
- 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.
- ItemCarotenoid cleavage dioxygenases (CCDs) of grape(Stellenbosch : Stellenbosch University, 2012-12) Dockrall, Samantha; Young, Philip R.; Vivier, Melane A.; Stellenbosch University. Faculty of AgriSciences. Dept. of Viticulture and Oenology. Institute for Wine Biotechnology.ENGLISH ABSTRACT: Plant carotenoid cleavage dioxygenases (CCD) are a family of enzymes that catalyse the oxidative cleavage of carotenoids and/or apocarotenoids. Carotenoids are synthesised in plastids (primarily chloroplasts and chromoplasts), where they are involved in light-harvesting and protecting the photosynthetic apparatus from photo-oxidation. The carotenoid-derived apocarotenoids fulfil a number of roles in plants such as phytohormones, pollinator attractants and flavour and aroma compounds. Due to the floral and fruity characteristics that apocarotenoids contribute to wine, these C13 compounds have received interest in grapevine (Vitis vinifera L.). The CCD gene family in Arabidopsis consists of nine members, all encoding for enzymes that catalyse the cleavage of carotenoids. The enzymes in this family include 9-cis-epoxydioxygenases (NCEDs) and four classes of CCD. NCEDs and CCD7 and CCD8 are involved with plant hormone synthesis, e.g. abscisic acid (ABA) through cleavage by NCED and strigolactone (SL) through the sequential cleavage of carotenoids by CCD7 and CCD8, respectively. SLs are a fairly new class of plant hormone which are involved in several aspects of plant growth and development. The most extensively characterised role of SLs is their involvement in the inhibition of shoot-branching. CCD1 and CCD4 cleave a variety of carotenoids to form pigments and aroma compounds. For example, CCD1 forms β-ionone and β-damascenone, which are important varietal flavours of wine, and CCD4 is involved in synthesis of the pigment and aroma compounds of saffron and annatto. CCD1 enzymes symmetrically cleave the 9,10 (9’,10’) double bonds of multiple carotenoids to produce a C14 dialdehyde and two C13 products. Additional CCD1 cleavage activity at 5,6 (5’,6’) double bonds of lycopene has been reported. Previous studies have shown that CCD1 isolated from V. vinifera (VvCCD1) was able to cleave multiple carotenoid substrates in vitro, namely zeaxanthin, lutein and β-carotene at 9,10 (9’,10’) double bonds and both the 5,6 (5’,6’) and 9,10 (9’,10’) double bonds of lycopene. None of the other VvCCDs, except VvCCD4a have been isolated (but no functionality was illustrated) and characterised yet. CCD4 enzymes also cleave carotenoids at the 9,10 (9’,10’) double bond positions. The presence of plastid-target peptides implies that the CCD4 enzymes have continuous access to carotenoids. Therefore it is suggested that CCD4s are responsible for carotenoid maintenance, where CCD1s contribute towards volatile production. To test this hypothesis VvCCD1, VvCCD4a and VvCCD4b were isolated from V. vinifera (cv Pinotage) cDNA and cloned into a pTWIN1 protein expression vector. Substrate specificity of each VvCCD was tested by co-transforming a carotenoid accumulating E. coli strain with a CCD expression vector. Carotenoids synthesized by the bacteria were identified and quantified by UPLC-analysis, while the concentration of the apocarotenoids, were measured in the headspace of the bacterial cultures using HS-SPME-GC-MS. Several optimisations were done to minimize the natural degradation of the carotenoids; to ensure that the apocarotenoid formation is predominantly due to the enzymatic cleavage by the VvCCDs and not due to oxidation or other non-enzymatic degradation. The HS-SPME-GC-MS analysis indicated that all isoforms cleaved phytoene, lycopene and ε-carotene. Additionally VvCCD1 cleaved a carotenoid involved in photosynthesis, namely β-carotene, while VvCCD4a cleaves neurosporene and VvCCD4b cleaves neurosporene and ζ-carotene, carotenoids not involved in photosynthesis. This study has illustrated that VvCCD1 cleave carotenoids necessary for photosynthesis and VvCCD4s cleave carotenoids which were not present in berry tissue, suggesting their role in carotenoid maintenance. Therefore in planta substrates for CCD1 could possibly be C27 apocarotenoids generated from enzymatic cleavage through CCD4 (role in carotenoid maintenance), CCD7 and/or photo-oxidation, which are then transported from the plastid to the cytosol or possibly C40 carotenoids that are released during senescence or when the plastid membrane is damaged, thus releasing important aroma compounds. Thus the identification of the in vivo substrates has contributed to the understanding the in planta functions of these enzymes
- ItemCell differentiation in response to nutrient availability : the repressor of meiosis, RME1, positively regulates invasive growth in Saccharomyces cerevisiae(Stellenbosch : Stellenbosch University, 2003-03) Hansson, Guy Robert, 1974-; Bauer, Florian; Pretorius, I. S.; Stellenbosch University. Faculty of AgriSciences. Dept. of Viticulture and Oenology. Institute for Wine Biotechnology.ENGLISH ABSTRACT: Yeasts, like most organisms, have to survive in highly variable and hostile environments. Survival therefore requires adaptation to the changing external conditions. On the molecular level, specific adaptation to specific environmental conditions requires the yeast to be able: (i) to sense all relevant environmental parameters; (ii) to relay the perceived signals to the interior of the cell via signal transduction networks; and (iii) to implement a specific molecular response by modifying enzyme activities and by regulating transcription of the appropriate genes. The availability of nutrients is one of the major trophic factors for all unicellular organisms, including yeast. Saccharomyces cerevisiae senses the nutritional composition of the media and implements a specific developmental choice in response to the level of essential nutrients. In conditions in which ample nutrients are available, S. cerevisiae will divide mitotically and populate the growth environment. If the nutrients are exhausted, diploid S. cerevisiae cells can undergo meiosis, which produces four ascospores encased in an ascus. These ascospores are robust and provide the yeast with a means to survive adverse environmental conditions. The ascospores can lie dormant for extended periods of time until the onset of favourable growth conditions, upon which the spores will germinate, mate and give rise to a new yeast population. However, S. cerevisiae has a third developmental option, referred to as pseudohyphal and invasive growth. In growth conditions in which nutrients are limited, but not exhausted, the yeast can undergo a morphological switch, altering its budding pattern and forming chains of elongated cells that can penetrate the growth substrate to forage for nutrients. The focus of this study was on elements of the signal transduction networks regulating invasive growth in S. cerevisiae. Some components of the signal transduction pathways are well characterised, while several transcription factors that are regulated via these pathways remain poorly studied. In this study, the RMEt gene was identified for its ability to enhance starch degradation and invasive growth when present on a multiple copy plasmid. Rme1 p had previously been identified as a repressor of meiosis and, for this reason, the literature review focuses on the regulation of the meiotic process. In particular, the review focuses on the factors governing entry into meiosis in response to nutrient starvation and ploidy. Also, the transcriptional regulation of the master initiator of meiosis, IMEt, and the action of Ime1 p are included in the review. The experimental part of the study entailed a genetic analysis of the role of Rme1 p in invasive growth and starch metabolism. Epistasis analysis was conducted of Rme1 p and elements of the MAP Kinase module, as well as of the transcription factors, Mss11p, Msn1p/Mss10p, Tec1p, Phd1p and F108p. Rme1p is known to bind to the promoter of CLN2, a G1-cyclin, and enhances its expression. Therefore, the cell cyclins CLN1 and CLN2 were included in the study. The study revealed that Rme1 p functions independently or downstream of the MAP Kinase cascade and does not require Cln1 p or Cln2p to induce invasive growth. FL011/MUC1 encodes a cell wall protein that is required for invasive growth. Like the above-mentioned factors, Rme1 p requires FL011 to induce invasive growth. We identified an Rme1 p binding site in the promoter of FL011. Overexpression of Rme1p was able to induce FL01t expression, despite deletions of mss11, msn1, ttos, tee1 and phd1. In the inverse experiment, these factors were able to induce FL011 expression in an rme1 deleted strain. This would indicate that Rme1 p does not function in a hierarchical signalling system with these factors, but could function in a more general role to modify transcription.
- ItemCell wall profiling of tobacco leaves and grapes in the context of Botrytis cinerea infection(Stellenbosch : Stellenbosch University, 2021-03) Weiller, Florent; Moore, John P.; Vivier, Melane A.; Stellenbosch University. Faculty of Agrisciences. Dept. of Viticulture and Oenology. Institute for Wine Biotechnology.ENGLISH ABSTRACT: The plant cell wall has been shown to be at the centre of plant-biotic stress interactions. In the case of a pathogen encounter (e.g. fungi), the cell wall acts as the second barrier after the cuticle to stop pathogen penetration and tissue colonisation. The plant cell wall matrix composition and architecture influences the nature of resistance and susceptible responses to fungal pathogens. Botrytis cinerea, the fungus responsible for grey mold disease, causes worldwide crop losses. Understanding factors that differentiate susceptible from resistant plants is essential to develop new plant protection strategies against B. cinerea. In this study, genetically engineered plants with known resistance phenotypes, compared to the untransformed controls (with susceptible phenotypes) were used to understand the leaf cell wall changes either afforded by the transgenes introduced and/or the Botrytis infection process. The approach to investigate cell wall changes during Botrytis infection was also expanded to grapevine berry fruit. The method of choice was Comprehensive Microarray Polymer Profiling (CoMPP) technology, a high-throughput method for tracking cell wall matrix polysaccharide and protein composition and it was combined with monosaccharide profiling and various imaging tools. In the first part of this study, the leaves of nine tobacco (Nicotiana tabacum) lines: four overexpressing the known defence gene, grapevine polygalacturonase-inhibiting protein 1 (VviPGIP1), four overexpressing another known defence gene, the tobacco cinnamyl alcohol dehydrogenase 14 (NtCAD14) and the wild type SR1 were screened for cell wall compositional differences due to genetic overexpression in the absence of infection. Total lignin and monolignols were assayed using Py-GC-MS, but results showed limited variations between the different plant lines. CoMPP and GC-MS analysis for cell wall composition and monosaccharide content showed variation in homogalacturonan (HG) methylesterification patterning between the various transgenic plant lines. Arabinogalactan proteins (AGPs) and extensins increased in the majority of the VviPGIP1 lines. These results suggest that PGIP overexpression probably influences pectinmethylesterase (PME) enzyme activity and affects glycoprotein organisation. Following these results, more in-depth analysis continued during infection of PGIP plants. Infection experiments were conducted using B. cinerea on leaves of VviPGIP1 tobacco lines, compared to the wild type as control. Lesion size differences were observed from 96 hours post inoculation (hpi) with reduced lesions in the transgenic lines compared to the wild type, confirming the known resistance responses of the transgenic plants to the fungus. Cell wall alterations were followed in the 72 hpi period, showing HG degradation with RG-I signal increase, whereas the cellulose-xyloglucan network was mostly unaffected. Extensins and AGPs accumulated at and around the lesions, while distal non-infected leaves showed matrix changes from 72 hpi, with reorganisation of the cellulose/xyloglucan network and in the homogalacturonan methylesterification patterning, indicative of a systemic response. A typical Botrytis infection with cell wall depectination exposed less hemicellulose polysaccharides. In parallel, the plant seemed to build a defensive response to the infection with accumulation of defence related proteins at the lesion and in distal leaves. Unlike the wild type, the transgenic plants response was efficient in restricting Botrytis progression from 72 hpi onwards. In the last part of this study berries, at three developmental stages (veraison, post-veraison and ripe), from four Vitis vinifera cultivars (Cabernet Sauvignon, Sauvignon Blanc, Dauphine and Barlinka grape berries), were infected with B. cinerea. Ripe grapes from all four cultivars developed symptoms and showed cell wall degradation with cultivar differences were noted, while very few successful B. cinerea infections on veraison and post-veraison grapes were observed. This is in line with the generalised view that grapevine berries display ontogenic resistance in the greener developmental stages, although there are known exceptions. Cabernet Sauvignon was the least susceptible cultivar to B. cinerea and displayed a delayed lesion development in our experimental conditions. The infected grapes from all the cultivars were characterised by altered HG methylesterification patterning, extensin reorganisation, as well as glucan accumulation as the infection progressed. This work has brought new insights to existing efforts to fully characterise the role of the grapevine PGIP1 gene in plant cell wall modifications, in the presence and absence of B. cinerea infection. It provides further proof that small changes in the cell wall matrix contribute to the possible priming of plants to resist and overcome infection. Moreover, the similarities and differences observed between tobacco leaves and grape berry cell walls during Botrytis infection will help to conduct targeted experiments and to complement the existing models on plant cell wall – B. cinerea interactions.
- ItemCharacterisation of grapevine berry samples with infrared spectroscopy methods and multivariate data analyses tools(Stellenbosch : Stellenbosch University, 2015-04) Musingarabwi, Davirai M.; Vivier, Melane A.; Nieuwoudt, Helene; Stellenbosch University. Faculty of Agrisciences. Dept. of Viticulture and Oenology. Institute for Wine Biotechnology.ENGLISH ABSTRACT: Grape quality is linked to the organoleptic properties of grapes, raisins and wine. Many advances have been made in understanding the grape components that are important in the quality of wines and other grape products. A better understanding of the compositional content of grapes entails knowing when and how the various components accumulate in the berry. Therefore, an appreciation of grape berry development is vitally important towards the understanding of how vineyard practices can be used to improve the quality of grapes and eventually, wines. The more established methods for grape berry quality assessment are based on gravimetric methods such as colorimetry, fluorescence and chromatography. These conventional methods are accurate at targeting particular components, but are typically multi-step, destructive, expensive, polluting procedures that might be technically challenging. Very often grape berries are evaluated for quality (only) at harvest. This remains a necessary exercise as it helps viticulturists and oenologists to estimate some targeted metabolite profiles that are known to greatly influence chemical and sensory profiles of wines. However, a more objective measurement of predicting grape berry quality would involve evaluation of the grapes throughout the entire development and maturation cycle right from the early fruit to the ripe fruit. To achieve this objective, the modern grape and wine industry needs rapid, reliable, simpler and cost effective methods to profile berry development. By the turn of the last millennium, developments in infrared instrumentation such as Fourier-transform infrared (FT NIR) and attenuated total reflectance Fourier-transform infrared spectroscopy (ATR FT-IR) in combination with chemometrics resulted in the development of rapid methods for evaluating the internal and external characteristics of fresh fruit, including grapes. The advancement and application of these rapid techniques to fingerprint grape compositional traits would be useful in monitoring grape berry quality. In this project an evaluation of grape berry development was investigated in a South African vineyard setting. To achieve this goal, Sauvignon blanc grape berry samples were collected and characterised at five defined stages of development: green, pre-véraison, véraison, post-véraison and ripe. Metabolically inactivated (frozen in liquid nitrogen and stored at -80oC) and fresh berries were analysed with FT-IR spectroscopy in the near infrared (NIR) and mid-infrared (MIR) ranges to provide spectral data. The spectral data were used to provide qualitative (developmental stage) and quantitative (metabolite concentration of key primary metabolites) information of the berries. High performance liquid chromatography (HPLC) was used to separate and quantify glucose, fructose, tartaric acid, malic acid and succinic acid which provided the reference data needed for quantitative analysis of the spectra. Unsupervised and supervised multivariate analyses were sequentially performed on various data blocks obtained by spectroscopy to construct qualitative and quantitative models that were used to characterise the berries. Successful treatment of data by principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA) gave statistically significant chemometric models that discriminated the berries according to their stages of development. The loadings from MIR models highlighted the important discriminant variables responsible for the observed developmental stage classification. The best calibration models to predict metabolite concentrations were obtained from MIR spectra for glucose, fructose, tartaric acid and malic acid. The results showed that both NIR and MIR spectra in combination with multivariate analysis could be reliably used to evaluate Sauvignon blanc grape berry quality throughout the fruit’s development cycle. Moreover, the methods used were fast and required minimal sample processing and no metabolite extractions with organic solvent. In addition, the individual major sugar and organic acids were accurately predicted at the five stages under investigation. This study provides further proof that IR technologies are robust and suitable to explore high-throughput and in-field application of grape compound profiling.
- 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.
- ItemCharacterisation, evaluation and use of non-Saccharomyces yeast strains isolated from vineyards and must(Stellenbosch : Stellenbosch University, 2004-03) Jolly, N. P. (Neil Paul); Pretorius, I. S.; Augustyn, O. P. H.; Stellenbosch University. Faculty of AgriSciences. Dept. of Viticulture and Oenology. Institute for Wine Biotechnology.ENGLISH ABSTRACT: Wine is the product of a complex biological and biochemical interaction between grapes and different microorganisms (fungi, yeasts, lactic acid bacteria and acetic acid bacteria, as well as the mycoviruses and bacteriophages affecting them) in which yeasts play the most important role regarding the alcoholic (primary) fermentation. These wine-associated yeasts can be divided into Saccharomyces and non-Saccharomyces yeasts. During fermentation, there is a sequence of dominance by the various non-Saccharomyces yeasts, followed by Saccharomyces cerevisiae, which then completes the fermentation. This is especially evident in spontaneously fermenting must, which has a low initial S. cerevisiae concentration. Some non- Saccharomyces yeasts can also be found throughout the fermentation. The non- Saccharomyces presence in the fermentation can affect wine quality, either positively or negatively. A positive contribution could be especially useful to improve wines produced from grape varieties with a neutral flavour profile due to non-optimal climatic conditions and/or soil types. As part of a comprehensive South African research programme, the specific objectives of this study were: the isolation of indigenous non-Saccharomyces yeasts from vineyards and musts; the identification of these isolates; the characterisation and evaluation of predominant species under winemaking conditions; and the development of a protocol for their use in enhancing wine quality. Initially, 720 isolates representing 24 different species, were isolated from grape (vineyard) and must samples taken over three vintages from four distinctly different wine producing regions. The isolates were characterised and grouped utilising biochemical profiles and DNA karyotyping, whereupon representative isolates were identified. The yeast species that had the highest incidence of predominance in the vineyard was Kloeckera apiculafa. However, some vineyard samples were characterised by low numbers or absence of this yeast, which is not according to generally accepted norms. Other species that also predominated in a few of the vineyard samples were Candida pulcherrima, Kluyveromyces thermofolerans, Rhodotorula sp. and Zygosaccharomyces bailii. Generally, there was a greater diversity of yeasts in the processed must than from the vineyard samples. Furthermore, while each sample showed a different yeast population, no pattern linking species to climatic zone was observed. Four species i.e. Candida collieulosa, Candida pulcherrima, Candida stel/ata and Kloeckera apiculata, were found to predominate in grape must samples. Representative strains consequently received further attention during laboratory and small-scale winemaking trials. A protocol was developed whereby individual species could be used in co-inoculated fermentations with S. cerevisiae in the small-scale production of wine. An improvement in wine quality was achieved and it was found that there was a link between specific species and grape cultivar. The ability of C. pulcherrima to improve Chenin blanc wine quality was investigated further. Results over three vintages showed that the wine produced by the co-inoculated fermentation was superior to that of a reference wine (produced by S. cerevisiae only). The improvement in wine quality was not linked to increased ester content nor were the standard chemical analyses adversely affected. The effects of pH and wine production parameters i.e. 802, fermentation temperature and use of di-ammonium phosphate (DAP), on this yeast followed the same pattern as that known for S. cerevisiae. This study was successfully completed and the developed protocol can be used for the improvement of Chenin blanc wine where additional aroma and quality is needed.
- ItemCharacterization of Chenin Blanc wines produced by natural fermentation and skin contact : focus on application of rapid sensory profiling methods(Stellenbosch : Stellenbosch University, 2014-12) Weightman, Jayne; Nieuwoudt, Helene; Setati, Mathabatha Evodia ; Stellenbosch University. Faculty of AgriSciences. Dept. of Institute for Wine Biotechnology.ENGLISH ABSTRACT: Producers of South African (SA) dry and semi-dry Chenin blanc table wines are currently experimenting with winemaking techniques to modulate the flavours of the predominantly fruity styles of this genre. An important stage during wine style development is sensory profiling paired with consumer acceptance testing, before wine is produced on industrial scale. With those aforementioned goals in mind, this study was conducted in partnership with two commercial SA wine cellars. The main focus of the study was an investigation into the treatment effects of two winemaking techniques, respectively grape skin contact and natural fermentation, on the sensory profiles of experimentally produced Chenin blanc wines. Results obtained with descriptive sensory analysis (DA) of the wines were compared to those obtained by two rapid sensory profiling methods, namely projective mapping (PM) and frequency of attribute citation (FC). A consumer preference study was also done on the wines. In order to understand the treatment effects better, the dominant non-Saccharomyces yeasts that were present during the natural fermentations were identified using polymerase chain reaction (PCR), while the major volatile chemical compounds were identified with chromatography and mass spectrometry. The sensory and chemical profiles of the naturally fermented wines were significantly different from those of the inoculated wines. PCR analysis identified some of the yeasts present during alcoholic fermentation. In comparison to the inoculated fermented wines, the naturally fermented wines were generally perceived to have more intense and riper tropical fruity aromas, with enhanced sweetness and reduced intensities of sourness, bitterness and astringency. The wines fermented on the skins (FoS) had lower ester and volatile thiol concentrations than the control wines (with no skin contact) and limited skin contact wines. Sensory attributes linked to the FoS wines included aromas of dried fruit, dried grass and a vegetative character, with an increased sour and bitter taste and astringent mouthfeel. In contrast, the wines that were produced with limited skin contact (12 hours) retained their tropical fruity aromas better than the FoS wines. Limited skin contact seemed to have had a less harsh effect on the taste and mouthfeel than the FoS wines. A consumer study was done to establish a Generation Y consumer group’s (18-35 years) preference for the different treated wines. Overall, the naturally fermented wines, which were described as having a strong tropical fruit character, were preferred. The FoS wines were generally disliked by the consumers. Results obtained from the three sensory analysis methods, respectively DA, PM and FC, were similar, thereby confirming the suitability of the rapid methods PM and FC, to extract qualitative information from the sensory profiling of white wine. The results of this study made a significant contribution towards validation of rapid sensory methods for wine evaluation, which are particularly valuable in the context of sustainability and technology transfer to research and industry alike. The knowledge gained on the chemical profiles of SA Chenin blanc is novel and this is one of the first reports on the volatile thiol content of SA Chenin blanc wine.
- ItemCoevolution of Saccharomyces cerevisiae and Lactobacillus plantarum : engineering interspecies cooperation(Stellenbosch : Stellenbosch University, 2018-03) Du Toit, Sandra Christine; Bauer, Florian; Rossouw, Debra; Du Toit, Maret; Stellenbosch University. Faculty of AgriSciences. Dept. of Viticulture and Oenology. Institute for Wine Biotechnology.ENGLISH ABSTRACT: Microbial interactions are ubiquitous in nature and play a vital role in economically important industrial processes like winemaking. Saccharomyces cerevisiae and Lactobacillus plantarum are important species responsible for the completion of alcoholic and malolactic fermentation (AF and MLF) respectively. Understanding how these species interact with each other and their environment is important to better manage successful completion of AF and MLF. However, the complexity of the wine matrix makes it nearly impossible to study these interactions in a natural environment and synthetic ecological systems can therefore be used to overcome these difficulties. This study was designed to establish a co-dependent, mutualistic relationship between S. cerevisiae and Lb. plantarum in order to gain insights into the cooperation between species, how pH, temperature, and inoculation dosages influences the interaction, and how the interaction evolves over time. The interaction, centered on the reciprocal exchange of amino acids, was established between the lysine auxotrophic strain S. cerevisiae THI4 and the isoleucine, alanine, valine, and methionine auxotrophic strain Lb. plantarum B038. Different combinations of amino acids were omitted from the chemically defined synthetic grape juice-like media in order to find an amino acid treatment which promoted the best growth for both microorganisms. B038 showed excellent growth when cocultured with THI4 for all the amino acid treatments, but THI4 struggled to grow under these conditions. The two treatments selected for further experiments were the Lys-Ile (lysine and isoleucine omitted) and Lys-Val (lysine and valine omitted) treatments since THI4 showed the best growth under these conditions. Lower temperature and pH conditions had a negative effect on the growth and malic acid consumption of B038, but when co-cultured with THI4 the yeast appeared to stimulate the growth of the bacteria under both selective and control conditions. THI4 continued to show poor growth performance and sugar consumption under these conditions. However, when THI4 and B038 were inoculated at cell densities with similar biomass, the growth of THI4 improved significantly. It was expected that THI4 and B038 would show poor growth when grown in the absence of their respective auxotrophic amino acids and support of their respective partner. This proved true for all the amino acid treatments except when B038 was grown in the absence of lysine and valine. B038’s ability to grow under these conditions was hypothesized to be linked to the uptake of glutamine and the production of γ-Aminobutyric acid (GABA), but further research is still required to investigate this. Over continuous rounds of fermentation, THI4 adapted to the imposed selective conditions by increasing its consumption of glucose while cell density remained the same. Whether this is linked to increased ethanol production still needs to be determined. No significant changes were observed in B038 after coevolving the strains. This study provides relevant insights into the industrially important interaction between S. cerevisiae and Lb. plantarum and also provides a basis for future work to create optimised yeast-bacteria pairings for both industrial applications in winemaking and to investigate the genetic changes involved in the establishment of cooperative interactions between species.
- ItemConstruction of recombinant Saccharomyces cerevisiae strains for starch utilisation(Stellenbosch : Stellenbosch University, 2002-12) Eksteen, Jeremy Michael; Pretorius, I. S.; Van Rensburg, P.; Stellenbosch University. Faculty of AgriSciences. Dept. of Viticulture and Oenology. Institute for Wine Biotechnology .ENGLISH ABSTRACT: Starch-containing agricultural crops are widely available as feedstocks for the production of fuel ethanol, potable spirits or beer, single-cell protein (animal feed) and high-fructose corn syrups (sweeteners). Starch-rich crops, such as maize, rye, barley and wheat, are usually used for the production of whisky. One of the first steps in the production of whisky is to boil the raw starch at temperatures exceeding 100°C. This gelatinisation step is performed to disrupt and solubilise the starch granules to make them more accessible for enzymatic hydrolysis. After this cooking process, the starch is liquefied by a-amylase and then saccharified by glucoamylase and a debranching enzyme. Lipomyces kononenkoae and Saccharomycopsis fibuligera secrete highly effective a-amylases and glucoamylases, making them two of the most efficient raw-starchdegrading yeasts known. However, L. kononenkoae and S. fibuligera cannot be used in existing industrial fermentations because of their low ethanol tolerance, slow growth rate, catabolite repression, poorly characterised genetics and lack of GRAS (Generally Regarded As Safe) status. This study is divided into two sections. The aim of the first section was to clone a gene (LKA2) encoding a novel starch-degrading enzyme, a second a-amylase (Lka2p) from L. kononenkoae. LKA2 was cloned into a multicopy plasmid, the yeast episomal plasmid, YEp352, under the control of the phosphoglycerate kinase promoter (PGK1 p) and terminator (PGKh) expression cassette. This recombinant plasmid was designated pJUL3 and transformed into a laboratory strain of S. cerevisiae, I1278b. Plate and liquid assays revealed that the recombinant yeast secreted active a-amylase into the medium. The optimum pH for Lka2p was pH 3.5 and the optimum temperature 60°C. The aim of the second part of the study was to construct recombinant strains of S. cerevisiae secreting a-amylase and/or glucoamylase. The individual genes were cloned into a yeast-integrating plasmid, Ylp5, under the control of the PGK1p-PGK1.,-expression cassette. Two indigenous yeasts were selected on the basis of their ability to utilise raw starch, L. kononenkoae and S. fibuligera, as gene donors. Eight constructs containing the L. kononenkoae a-amylase genes, LKA 1 and LKA2, and the S. fibuligera a-amylase (SFA 1) and glucoamylase (SFG1) genes were prepared: four single-cassette plasmids expressing the individual coding sequences under the control of the PGK1 p-PGK1.,- expression cassette, resulting in plPLKA 1, pIPLKA2, plPSFA 1 and pIPSFG1, respectively; two double-cassette plasm ids (expressing both LKA 1 and LKA2 under the control of the PGK1p-PGK1 .,-expression cassette, and SFA 1 and SFG1 under their respective native promoters and terminators), resulting in pIPLKA1/2 and pIPSFAG, respectively, and two single-cassette plasmids expressing SFA 1 and SFG1 with their native promoters and terminators, resulting in pSFA 1 and pSFG1, respectively. The respective constructs were transformed into a laboratory strain of S. cere visiae , L1278b. By homologous recombination, each plasmid was integrated into the yeast genome at the ura3 locus. S. cerevisiae L:1278b that had been transformed with plPLKA 1/2, LKA 1 and LKA2 under the control of the PGK1 rrPGK1,expression cassette resulted in the highest levels of a-amylase activity when assayed for amylolytic activity in a liquid medium. This recombinant strain resulted in the most efficient starch utilisation in batch fermentations, consuming 80% of starch and producing 6 gIL of ethanol after 156 hours of fermentation. The strain expressing SFG1 under the control of the PGK1rrPGK1,expression cassette gave the highest levels of glucoamylase activity.' These results confirmed that co-expression of a-amylase and/or glucoamylase synergistically enhance starch degradation. This study paves the way for the development of efficient starch-degrading strains of S. cerevisiae for the production of whisky, beer and biofuel ethanol.
- ItemConsumer sensory perception of South African Chenin blanc wine(Stellenbosch : Stellenbosch University, 2018-03) Mapheleba, Andiswa; Nieuwoudt, Helene; Muller, Nina; Pentz, Chris; Oertle, Ivan; Stellenbosch University. Faculty of AgriSciences. Dept. of Viticulture and Oenology. Institute for Wine Biotechnology.ENGLISH ABSTRACT: In the food and beverage industries, the understanding of consumer behaviour and the sensory characteristics of products are important to producers as they aid in the implementation of communication and marketing strategies. South African Chenin blanc is a white wine variety that is characterised by diverse sensory profiles, an attribute that is considered as a strength of the variety from a technical wine production perspective. Accordingly, the wine industry has become highly interested in gaining knowledge about the perceptions of consumers regarding Chenin blanc styles in particular. The main aim of this study was to investigate the sensory and overall perceptions of Chenin blanc wine among South African consumers. Sensory analysis was conducted on three different Chenin style wines, namely fresh, complex unwooded and complex wooded wines using descriptive analysis (DA) with a trained panel. Among consumers, free listing and CATA were carried out to explore their sensory perceptions through encouraging them to freely describe their tasting experience and the selection of the perceived of aroma attributes obtained from DA. Thereafter, an exploratory study with the aid of a survey questionnaire was conducted to obtain insights of the consumers’ consumption, purchase behaviour and general perceptions about Chenin blanc wine.. Industry professionals from different disciplines of the wine industry, participated in the study by providing their viewpoints on aspects regarding the position of Chenin blanc in the SA wine industry through a self-completed questionnaire. The sensory attributes that were mostly provided by the consumers in free listing were fruit, citrus, tropical, honey, wood, earthy, nutty and fresh. A significantly lower number of attributes was perceived by consumers with CATA. The important non-sensory attributes listed by the consumers included their emotions, context of usage (occasion) and pleasure. They generally displayed an inclination towards buying wines with simple sensory label descriptors. According to the industry professionals, wine labelling and initiatives by the SA wine industry should be simple and relatable. Furthermore, Chenin blanc would highly benefit from cultivar-specific shows, due to its wide wine style spectrum. This study contributed towards a better understanding of the perceptions of SA wine consumers about Chenin blanc wine of the two respondent groups to aid in the understanding of the market and the wine industry, as well as their prospective roles in the future of Chenin blanc in SA.
- ItemDefining the chemical features of wine perception(Stellenbosch : Stellenbosch University, 2018-03) Fairbairn, Samantha; Bauer, Florian; Da Silva Ferreira, A. C.; Stellenbosch University. Faculty of AgriSciences. Dept. of Viticulture and Oenology. Institute for Wine Biotechnology.ENGLISH ABSTRACT: All wines evoke a product recognition, regardless of quality and cultivar, but what is the origin of this feature? The prevalence of this wine concept suggests that its formation occurs independent of the varietal, and ageing-related aromas, and is therefore potentially a function of yeast metabolism. Yeast utilise the nutrients present in grape must to produce biomass, and metabolites which ultimately signify the conversion of grape juice to wine. Consequently, the nutrient composition is highly influential on the aromatic outcomes of alcoholic fermentation. Synthetic grape must is widely used to evaluate all facets of the fermentation process but there remains much to learn. In this study, the impact of two nutrients, namely, amino acids and anaerobic factors, were evaluated with regard to their impact on yeast growth and aroma production under fermentative conditions. This work also examines the extent to which yeast de novo metabolism, both primary and secondary metabolism, contributes to the formation of the wine-like feature. In a single amino acid context, a linear relationship was apparent between the amino acid concentration and the production of their associated volatile products. This relationship was evaluated in more complex amino acid mixtures and as expected, this linear relationship was lost. Nonetheless, a significant degree of responsiveness between the amino acid and its catabolites remained. The impact of sterol (plant or yeast derived) or unsaturated fatty acid treatments, individually, as well as in combinations, were compared for their contributions to biomass formation and aroma production. Sterols had a greater impact on biomass development, as the fermentations treated with only unsaturated fatty acids displayed a poorer response. Moreover, they differently impacted aroma production. The unsaturated fatty acid lowered the production of acetate esters, medium chain fatty acids and their esters, whereas sterol supplementation generally bolstered the production of all compounds measured. This work highlights the importance of anaerobic factor management during winemaking. Although these nutrients certainly impact wine aroma, this study also sought to examine the degree to which these nutrients contribute to wine (product) recognition. Using a novel fermentation-based approach, Saccharomyces cerevisiae converted a synthetic grape must into a wine-like product. These synthetic products underwent sensory evaluations to rate the product’s resemblance to wine as well as to describe the aroma. This sensory data was used as a decision-making tool to decide upon treatments to be studied in subsequent fermentations. Ultimately, a wine-like character was created by altering the anaerobic factor composition of a synthetic grape must. The use of this synthetic grape must would allow for the more meaningful sensory characterisation of these synthetic products, in addition to providing a wine-like matrix used to evaluate the sensory implications of wine odorants.
- ItemThe deletion and overexpression of two esterase genes, IAH1 and TIP1, in Saccharomyces cerevisiae to determine their effects on the aroma and flavour of wine and brandy(Stellenbosch : Stellenbosch University, 2002-12) Hignett, Jason Satch; Du Toit, M.; Pretorius, I. S.; Lambrechts, M. G.; Stellenbosch University. Faculty of AgriSciences. Dept. of Viticulture and Oenology. Institute for Wine Biotechnology .ENGLISH ABSTRACT: No single chemical constituent can be accredited with giving wine and brandy their overall aroma and flavour. The aroma and flavour of wine and brandy are rather attributed to a number of chemical constituents reacting together and it is these reactions that give the beverage its character. Certain chemicals within wine and brandy do, however, make larger contributions to the flavour. These include the esters, terpenes and volatile acids, although others also exist. Esters are a large group of volatile compounds with variable aroma and flavour characteristics, including banana-like (isoamyl acetate), apple-like (ethyl caproate) and chemical/solvent-like (ethyl acetate). Esters are produced as secondary metabolites during the conversion of sugar to ethanol and are formed when an alcohol binds with a fatty acid. Chemically, ester metabolism is well documented and understood; however, much work still needs to be done on a genetic level. The yeast strain used during fermentation is one of the most important factors contributing to the type and quantity of esters produced. This is due to differences in genetic makeup. The metabolism of esters is controlled largely on a genetic level, with numerous genes being involved. The alcohol acetyltransferase genes are involved in ester anabolism, whilst esterase genes are involved in ester catabolism. Esterases have a negative effect on the overall level of esters within an alcoholic beverage, as they are capable of reducing the number of esters and are thus capable of altering the beverage's aroma and flavour profile. The IAH1 and the TIP1 gene products are believed to encode for two such esterases. The objective of this study was to investigate the contribution of the IAH1 and TIP1 genes to the level of esters in both wine and brandy. This was accomplished by using two approaches. Firstly, the above genes were disrupted using a polymerise chain reaction (PCR)-generated disruption cassette homologous to either the IAH1 or the TIP1 gene. These cassettes were integrated into the industrial wine yeast, Saccharomyces cerevisiae strain VIN13. The integrations were verified by Southern blot analysis to produce yeasts VIN13-~IAH1 and VIN13-~TIP1; however, only a single copy of each was disrupted. Secondly, the IAH1 and the TIP1 genes were cloned from S. cerevisiae using PCR into plasmid pj between the phosphoglycerate kinase gene (PGK1) promoter and terminator, producing plasmids pJ-IOE1 and pJ-TOE1. The PGK1 promoter has previously been shown to constitutively express genes at high levels. These new constructs were then used as template for PCR to produce two overexpression cassettes, one for IAH1 and the other for TlP1. These cassettes were integrated into S. cerevisiae VIN13 and verified by Southern blot analysis to produce strains VIN13-IOE1 and VIN13-TOE1. The above yeast strains including VIN13 were used for the production of wines and base wines from Colombard must. Reverse-transcriptase (RT-PCR) confirmed that the VIN13-IOE1 and VIN13-TOE1 strains overexpressed the appropriate gene at a higher level than the control VIN13 strain. The VIN13-AIAH1 disrupted strain showed no difference in expression level to that of the control strain, whilst VIN13-ATIP1 showed lower levels of expression than that of the control strain. VIN13-IOE1 behaved as expected, with a decrease of between 30% and 60% in the total ester level in the wine and base wine respectively, a 30% decrease in the total acid level and no change in the higher alcohol level. The VIN13-AIAH1 strain showed no difference to the control wine, most likely as this strain still expressed the IAH1 gene at levels consistent with the control strain. VIN13-TOE1 behaved in an unexpected manner - instead of hydrolysing esters, it appeared to produce them. This increase in the total ester level was most noticeable during distillation, when a 20% increase took place. Another unexpected occurrence was a large decline in the total acid level, with acetic acid being the most significant contributor, decreasing by up to 78%. This is a very favourable finding, as acetic acid is a known spoilage molecule and is a cause of sluggish/stuck fermentations. VIN13-ATIP1 behaved in an opposite manner to VIN13-TOE1, with higher total acid levels and slightly decreased total ester levels, especially during distillation. Neither affected the total higher alcohol levels. Sensorially, the only significant difference in the wine samples was for the fruity flavour. A panel of judges distinguished that VIN13-TOE1 was fruitier than the other wines, with VIN13-ATIP1 being the least fruity. This study again proves the significant impact that a single gene can have on the chemical makeup of wine and brandy. The relatively simple genetic alteration of an organism can drastically change and improve not only the organoleptic properties of the organism, but its viability as well. These alterations can produce more favourable organisms with more desirable characteristics for the fermenting beverage industry to produce products of higher quality and better suitability.
- 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.
- ItemEffect of foliar Nitrogen and Sulphur spraying on white wine composition ( Vitis vinifera L.cv. Chenin Blanc and Sauvignon Blanc)(Stellenbosch : Stellenbosch University, 2018-12) Bruwer, Freda Aléta; Buica, Astrid; Stellenbosch University. Faculty of AgriSciences. Dept. Viticulture & Oenology & Institute for Wine Biotechnology.ENGLISH ABSTRACT: Chenin Blanc and Sauvignon Blanc, as the most planted wine cultivars in South Africa, are of great interest to researchers worldwide, due to its increased high wine quality. Wine quality is interlinked with wine aroma. Vine nitrogen fertilization influence the vine physiology and composition of the grapes, and enhanced aroma expression. By addressing Yeast Assimilable Nitrogen (YAN) deficiency with foliar fertilization, during the ripening season, to low nitrogen containing vines, the aroma potential of the wines can be potentially influenced. The main aim of this research study was to assess the influence of different foliar fertilization treatments on Chenin Blanc and Sauvignon Blanc vines planted in various locations in South Africa. For each season, two vineyards with a history of producing low nitrogen content grapes were used, one vineyard per cultivar. The vineyards received sulphur and nitrogen foliar treatments twice before véraison. During winemaking, the juices and wines underwent analysis for non-volatile and volatile content. The wines underwent maturation for three and nine months, and then sensorially and chemically analysed. In Chapter 2 the various wine compounds and classes of compounds present in Chenin Blanc and Sauvignon Blanc wines were analysed. The specific characteristics, aroma composition and its implications on the sensory perception of the cultivars were reviewed. The influence and contribution of different fertilization practices on the chemical compounds and resulting wine’s aromatic expression were investigated. The first part of the research study investigated the effect of foliar fertilization on the non-volatile content in the juices and wines. In Chapter 3, the nitrogen containing foliar fertilization applications increased the YAN levels. This increase is relevant not only for yeast metabolism, but also for the aromatic potential of a wine, as certain amino acids being precursors of aroma compounds. Glutathione were also influenced by the treatments for both years and both cultivars, but the trends were not as evident as with YAN. The second part of the study assessed the effect of various fertilization treatments on the volatile content of the juices and aged wines. Sensory analysis and chemical analysis were used to assess the wines after three and nine months of bottle maturation. Chapter 4 highlighted that sulphur containing foliar treatments influenced the volatile content of major volatiles and volatile thiols. The overall volatile content of the wines was very similar but identified a clear vintage and age effect during maturation. Sensory analysis classified the Chenin Blanc wine with ‘tropical’ and ‘fruity’ aromas, while Sauvignon Blanc wines had prominent ‘tropical’, ‘passion fruit’, and ‘grapefruit’ aromas. During bottle maturation, some notes and aroma characters were maintained but their frequency of citations changed. The results of this research study contributed to the knowledgebase on South African Chenin Blanc and Sauvignon Blanc wines, but also concluded that foliar fertilization can influence the non-volatile and volatile content of wines. South African winemakers and the industry can use this information to make decisions at the viticulture and winemaking level to produce wines with more desirable sensory attributes.
- ItemThe effect of grape temperature on the phenolic extraction and sensory perception of Méthode Cap Classique wines(Stellenbosch : Stellenbosch University, 2017-03) Mafata, Mpho; Van Jaarsveld, Francois; Du Toit, Wessel J.; Buica, Astrid; Stellenbosch University. Faculty of AgriScience. Dept. of Viticulture and Oenology. Institute for Wine Biotechnology.ENGLISH ABSTRACT: The first sparkling wine in South Africa was released in 1971. The South African Cap Classique Producers Association (CCPA), formed for the appreciation of Méthode Cap Classique (MCC) traditional style sparkling wines (TSW), was established in 1992 and has since contributed to the growth of these wines on a competitive footing with the international market. Generally, studies on TSW have focused primarily on the foam capability, volatile composition and autolytic character of the wines and very little on phenolic content of the wines. Phenolic compounds are important quality indicators of wine. Their composition in wine is determined by various factors including grape variety, terroir, viticultural practice, and oenological practices. In this project, MCC wines were made by the traditional method using Chardonnay and Pinot noir grapes harvested from two regions (Robertson and Darling) and stored at 0, 10, 25 and 30ºC, over two vintages (2014 and 2015). The phenolic concentration of the wine samples throughout the winemaking process was analysed by spectrophotometer and the aroma and taste of the final 9 month old sparkling wines performed. The study was aimed at investigating the effect of the grape storage temperature on the phenolic content and the sensory properties of MCCs through a quantitative phenolic analysis. The study found that MCCs made from grapes stored at lower temperatures (0 and 10ºC) had lower total phenolic content, colour intensity and total hydroxycinnamates than wines made from grapes stored at higher temperatures (25 and 30ºC) showing that there was greater phenolic extraction from grapes stored at 25 and 30ºC. The total phenolics, as measured by spectrophotometer, was below the range cited in literature for Champagne made from the same cultivars. The sensory evaluation of the MCCs comprised a sorting analysis similar to that used for beers. Separating the aroma and taste sorting of the MCCs, the study showed a grouping of the MCCs according to temperature treatments for both vintages. There were, however, clear vintage differences in terms of the attributes cited and the frequency of citations. Based on frequency of citation, 2014 MCCs made from grapes stored at 0 and 10°C were described by judges as being fruity, fresh and crisp whilst those made from grapes stored at 25 and 30°C were described as having oxidised fruit, volatile acidity and solvent-like aromas. The judges perceived less oxidation and VA (in terms of the frequency of citation) in the aroma of 2015 MCCs, although higher temperature treatments were still associated with less desirable attributes compared to lower temperature treatments. Judges were better able to separate the Darling wines according to treatments compared to the Robertson wines. This study has shown that the grape storage temperature has an effect on the phenolic extraction and the sensory perception of MCCs aged 9-months with no changes in the phenolic content observed throughout winemaking.