Department of Viticulture and Oenology

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3-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.
The 3Ps (Profit, Planet, and People) of sustainability amidst climate change : a South African grape and wine perspective
(MDPI, 2021-03-08) Gbejewoh, Omamuyovwi; Keesstra, Saskia; Blancquaert, Erna
Conventional agriculture has made the search for sustainability urgent, more so with regards to climate change. This has extended to the grape and wine industry, an important industry in South Africa in terms of labor employment and foreign exchange. This paper aims to review the current state of knowledge with regards to the three pillars of sustainability and with regards to climate change. In order to understand sustainability in South Africa, a historical context is needed, because the welfare of farm workers still retains vestiges of past Apartheid. Ecological responsibility and higher profits are the main reasons for sustainable practices. Additionally, water use, chemical use, and soil erosion are important environmental sustainability concerns. With regards to climate change, in terms of economic sustainability, there will be winners and losers and social sustainability issues will intensify as changes occur in farms. Table grape producers are relatively more profitable than wine grape producers. Furthermore, pest, disease, irrigation pressure will worsen as the climate warms. However, there are long- and short-term adaptation strategies such as changes in viticulture practices and grape cultivars, respectively, to stem the effects of climate change, but this may be stymied by cost and farmers’ perceptions of climate change.
The 3Ps (profit, planet, and people) of sustainability: a South African grape and wine perspective
(Stellenbosch : Stellenbosch University, 2021-12) Gbejewoh, Omamuyovwi; Blancquaert, Erna; Keesstra, S.; Hoffman, W. H.; Stellenbosch University. Faculty of AgriSciences. Dept. of Viticulture and Oenology.
ENGLISH ABSTRACT: Ever since the discovery of the environmental impacts of modern production in agriculture, sustainability and sustainable production has been at the forefront of efforts to reduce the external pressures on the system. The initial focus of the sustainability model was only on the environment and was later expanded to include the economic and social dimensions as evidenced in the millennium and sustainable development goals of the United Nations. Industrial agricultural production produces its fair share of greenhouse gas emissions. However, the grape and wine sectors were traditionally not considered environmentally demanding. Regardless of this increased interest in sustainability and sustainable production, the question remains: What does sustainability mean? How to measure and achieve it? It is still hotly debated which is open to various subjective interpretations. This project was aimed at studying the three pillars of sustainability equally and together in the grape and wine sector in South Africa. The objectives of the project were to: (i) evaluate what sustainability and its three pillars mean and how climate change is affecting these three pillars, (ii) determine context-specific indicators for the three pillars of sustainability and (iii) finally assess the feasibility of balancing the three pillars in a farm. The results of the first objective showed that sustainability is still highly subjective as all the respondents defined it differently and the environmental dimension still dominated their perceptions of sustainability in its importance, but they considered the social dimension the most difficult to achieve. In terms of climate change, extremes like drought, temperature and rainfall variations affected profits and the gains seen in other wine-producing countries are not present in South Africa. With regards to the environment, water demand was severely increasing irrigation pressure followed by increased reliance on chemicals for pest control. Spill-over effects of the economic dimension affected the social dimension in terms of limited work opportunities and stagnant wages for workers. The results of the second objective showed that economic indicators selected as relevant speak to the precarious situation of grape and wine farmers. The environmental indicators considered relevant were interesting given that actual practices were different given various regional environmental contexts. While the social dimension showed that respondents believe in improving the welfare of workers but are limited in what they can do to improve this dimension given the economic situation of many farms. The final objective showed that even though combined improved environmental and social practices reduced the profitability of farms, only improved social practices had the least effect. This showed that even significant improvement in the social dimension did not have to impact the bottom line of farms adversely. However, these results should be interpreted with caution as it involves simulating a complex system. Finally, as this study was exploratory, more research is needed in terms of more diverse participants (foreign retailers and consumers), more rounds of indicator selection and simulating the entire farm and not just the production process.
Die aanwending van distillasieprodukte by die gisting van mos
(Stellenbosch : Stellenbosch University, 1958-12) Zeeman, A. S. (Adriaan Siebrits); Theron, C. J.; De Waal, C. T.; Stellenbosch University. Faculty of AgriSciences. Dept. of Viticulture and Oenology and Institute for Wine Biotechnology.
ENGLISH ABSTRACT: no abstract available
Additions of glutathione or specific glutathione-rich dry inactivated yeast preparation (DYP) to sauvignon blanc must : effect on wine chemical and sensory composition
(South African Society for Enology and Viticulture, 2017) Gabrielli, M.; Aleixandre-Tudo, J. L.; Kilmartin, P. A.; Sieczkowski, N.; Du Toit, W. J.
Although the addition of pure glutathione (GSH) is not allowed under current regulations, the concentration of this compound can be increased in wine through the addition of glutathione-enriched dry yeast preparations (DYP). These preparations have been observed to have antioxidant properties and could thus influence wine aroma and sensory characteristics. The main aim of this study was to investigate the effect of DYP and GSH juice additions on the sensory and chemical composition of Sauvignon blanc wine. Four juice additions were performed and compared against a control treatment: 5.5 mg/L of GSH; 0.4 g/L of DYP; 80 mg/L of GSH; 0.4 g/L of DYP plus 80 mg/L of GSH. After three months of bottling, the volatile and sensorial composition was investigated. The addition of DYP preparations to must increased the concentration of certain wine volatile compounds, with increased attributes of riper tropical fruit aromas, which was not always observed with the GSH additions. The addition of DYP influenced the concentrations of some volatile compounds, which modified the white wine aroma. The release of compounds other than GSH by the yeast products is proposed as the reason for these changes. The results observed in this study can assist winemakers to modify the aroma profile of Sauvignon blanc wines.
Altered fermentation performances, growth, and metabolic footprints reveal competition for nutrients between yeast species inoculated in synthetic grape juice-like medium
(Frontiers Media, 2018) Rollero, Stephanie; Bloem, Audrey; Ortiz-Julien, Anne; Camarasa, Carole; Divol, Benoit
The sequential inoculation of non-Saccharomyces yeasts and Saccharomyces cerevisiae in grape juice is becoming an increasingly popular practice to diversify wine styles and/or to obtain more complex wines with a peculiar microbial footprint. One of the main interactions is competition for nutrients, especially nitrogen sources, that directly impacts not only fermentation performance but also the production of aroma compounds. In order to better understand the interactions taking place between non-Saccharomyces yeasts and S. cerevisiae during alcoholic fermentation, sequential inoculations of three yeast species (Pichia burtonii, Kluyveromyces marxianus, Zygoascus meyerae) with S. cerevisiae were performed individually in a synthetic medium. Different species-dependent interactions were evidenced. Indeed, the three sequential inoculations resulted in three different behaviors in terms of growth. P. burtonii and Z. meyerae declined after the inoculation of S. cerevisiae which promptly outcompeted the other two species. However, while the presence of P. burtonii did not impact the fermentation kinetics of S. cerevisiae, that of Z. meyerae rendered the overall kinetics very slow and with no clear exponential phase. K. marxianus and S. cerevisiae both declined and became undetectable before fermentation completion. The results also demonstrated that yeasts differed in their preference for nitrogen sources. Unlike Z. meyerae and P. burtonii, K. marxianus appeared to be a competitor for S. cerevisiae (as evidenced by the uptake of ammonium and amino acids), thereby explaining the resulting stuck fermentation. Nevertheless, the results suggested that competition for other nutrients (probably vitamins) occurred during the sequential inoculation of Z. meyerae with S. cerevisiae. The metabolic footprint of the non-Saccharomyces yeasts determined after 48 h of fermentation remained until the end of fermentation and combined with that of S. cerevisiae. For instance, fermentations performed with K. marxianus were characterized by the formation of phenylethanol and phenylethyl acetate, while those performed with P. burtonii or Z. meyerae displayed higher production of isoamyl alcohol and ethyl esters. When considering sequential inoculation of yeasts, the nutritional requirements of the yeasts used should be carefully considered and adjusted accordingly. Finally, our chemical data suggests that the organoleptic properties of the wine are altered in a species specific manner.
Amelioration of smoke taint in wine using commercially available and legally permissible additives
(Stellenbosch : Stellenbosch University, 2019-04) Langa, Nongcebo Portia; McKay, Marianne; Stellenbosch University. Faculty of Agrisciences. Dept. of Viticulture and Oenology.
ENGLISH ABSTRACT: The changes experienced in climate in many parts of the world have led to an increase in incidences of wildfire, and it has been predicted that these events will become more prevalent over time. All fires release volatile compounds into the atmosphere, and if they occur near vineyards where grapes are ripening, smoke taint may be detected in wines made from these grapes. Smoke taint is a critical issue for wine producing regions of the world as smoky and unpleasant flavours and aromas are perceived in affected wines, and this may have serious economic implications for producers. A number of researchers have tried to understand smoke taint, and their research has shown that volatile phenols (VP) are chemical compounds responsible. Additional research has revealed that although guaiacol, 4-ethylguaiacol, and 4-methylguiacol were originally identified as chemical markers of smoke taint, other VPs such cresols, eugenol, and phenol derivatives also play a role in causing smoky and ashy flavours. Strategies to eliminate the problem have ranged from washing the grapes and harvesting by hand, to minimising skin contact and choosing yeast and bacteria for minimal impact, and marketing wines for early release. These techniques work but do not eliminate an important underlying issue: glycoconjugates. Glycoconjugates or glycosides (VPs bound to sugars) are compounds that act as precursors of smoke taint produced as a detoxification by-product by vines. Glycosides can be hydrolysed by acid and enzymes, which means wines have the potential to increase available VPs in the wine, despite great care being taken to minimise VPs. This study expands on previous strategies that have been used to ameliorate smoke taint by using commercially available and legally permissible products in South Africa and exploring their effectivity at different dosage levels. Grapes in this study were harvested and deliberately smoked in crates using a bee-smoker, which produced smoke generated from fynbos (indigenous vegetation) and pine needles. Activated charcoal, oak extract, polymer powder were used in the first part of this study to try and ameliorate the taint during winemaking. GC-MS analysis of treated wines and controls revealed that only activated charcoal at elevated levels decreased VPs chemically. Sensory analysis of treated wines and controls by a trained panel using Descriptive Analysis showed that oak extract did increase levels of eugenol and consequently increased the ‘woody’ attribute, thus somewhat masking the smoke aroma. None of the treatments were able to remove the smoke aroma and flavour satisfactorily, primarily because of ashy flavour on the palate, likely due to in-mouth enzymes hydrolysing VP-glycosides. Building on the data and knowledge accumulated during the first part of the study, the second part of the study attempted to reduce levels of volatile phenol glycosides by using β-glucosidases before treatment application for removing free volatiles (“release-and-remove”). The treatments used after the enzyme hydrolysis were activated charcoal, polymer powder, yeast hulls, and mannoproteins. Chemically, GC-MS showed that there were sharp increases of VPs after the addition of enzymes, and some success in subsequent removal of the free volatiles. Further work is needed to determine the optimum levels of treatment. The data in this study showed potential for β-glucosidases to be used in the winemaking process, not only to release VPs (for later removal) but to increase the expression of fruity aromas in the wine. Enzymes may help to release other compounds that contribute to wine flavour, thus masking some of the smoke taint. This study contributes to the improved understanding of methods that can be used for the removal or treatment of smoke taint, but the need for further work was highlighted. The use of β-glucosidases followed by multiple finings could be an option for producers after a fire incident has occurred near a vineyard during ripening of grapes.
Analysis of antifungal resistance phenotypes in transgenic grapevines
(Stellenbosch : Stellenbosch University, 2012-12) Du Plessis, Kari; Vivier, Melane A.; Stellenbosch University. Faculty of AgriSciences. Dept. of Viticulture and Oenology. Institute for Wine Biotechnology.
ENGLISH ABSTRACT: The latest strategies in the protection of crops against microbial pathogens are rooted in harnessing the natural, highly complex defense mechanisms of plants through genetic engineering to ultimately reduce the application of chemical pesticides. This approach relies on an in-depth understanding of plant-pathogen interactions to develop reasonable strategies for plant improvement. Among the highly specialized defense mechanisms in the plant’s arsenal against pathogen attack, is the de novo production of proteinaceous antimicrobial peptides (AMPs) as part of the plant’s innate immunity. These AMPs are small, cysteine-rich peptides such as plant defensins that are known for their broad-spectrum of antifungal activity. These plant defensin peptides have been found to be present in most, if not all plant species and the defensin encoding genes are over-represented in plant genomes. Most of these defensins are generally the products of single genes, allowing the plant to deliver these molecules relatively rapidly and with minimal energetic expense to the plant. These factors contribute to establishing AMPs as excellent candidates for genetic engineering strategies in the pursuit of alternative crop protection mechanisms. The first antimicrobial peptide identified and isolated from grapevine, Vv-AMP1, was found to be developmentally regulated and exclusively expressed in berries from the onset of ripening. Recombinantly produced Vv-AMP1 showed strong antifungal activity against a wide range of plant pathogenic fungi at remarkably low peptide concentrations in vitro, however, no in planta defense phenotype could thus far be linked to this peptide. In this study, the antifungal activity of Vv-AMP1 constitutively overexpressed in its native host (Vitis vinifera) was evaluated against grapevine-specific necrotrophic and biotrophic fungi. Firstly, a hardened-off genetically characterised transgenic V. vinifera (cv. Sultana) population overexpressing Vv-AMP1 was generated and morphologically characterized. In order to evaluate the in planta functionality of Vv-AMP1 overexpressed in grapevine, this confirmed transgenic population was subjected to antifungal assays with the necrotrophic fungus, B. cinerea and the biotrophic powdery mildew fungus, Erysiphe necator. For the purpose of infection assays with a biotrophic fungus, a method for the cultivation and infection with E. necator was optimized to generate a reproducible pathosystem for this fungus on grapevine. Detached leaf assays according to the optimized method with E. necator revealed programmed cell death (PCD) associated resistance linked to overexpression of Vv-AMP1 that can be compared to that of the highly resistant grapevine species, Muscadinia rotundifolia. Contrastingly, whole-plant infection assays with B. cinerea revealed that Vv-AMP1 overexpression does not confer V. vinifera with elevated resistance against this necrotrophic fungus. An in silico analysis of the transcription of defensin-like (DEFL) genes previously identified in grapevine was included in this study. This analysis revealed putative co-expression of these DEFL genes and other genes in the grapevine genome driven by either tissue- or cultivar specific regulation or the plant’s response to biotic and abiotic stress stimuli. In conclusion, this study contributed to our knowledge regarding Vv-AMP1 and revealed an in planta defense phenotype for this defensin in grapevine. In silico analysis of the DEFL genes in grapevine further revealed conditions driving expression of these genes allowing for inferences to be made regarding the possible biological functions of DEFL peptides in grapevine.
Analysis of endo-polygalacturonase activity in a recombinant yeast containing a reconstituted PGU1 gene
(Stellenbosch : University of Stellenbosch, 2009-03) Van Wyk, Herine; Divol, Benoit; University of Stellenbosch. Faculty of Agrisciences. Dept. of Viticulture and Oenology. Institute for Wine Biotechnology.
The PGU1 gene encodes an endo-polygalacturonase, an enzyme that degrades pectin. Although the presence and function of this gene is well characterized in Saccharomyces cerevisiae, its regulation is very complex and not yet fully understood. Yeast producing a highly active polygalacturonase (PG) during alcoholic fermentation could potentially improve filtration and turbidity and also enhance extraction of certain aroma compounds. This could replace the addition of expensive commercial enzyme preparations that often contain unwanted enzymes. The first objective of this study was to evaluate PGU1 expression in recombinant strains of S. cerevisiae that originally lacked the PGU1 gene. A functional PGU1 gene and its promoter were successfully re-introduced into their native position in the genomes of five wine strains. Three of these strains recovered PG activity while two did not transcribe the gene and subsequently lacked activity. The three strains that recovered activity were used in microvinification experiments to determine the effect of PG-producing yeast on the aroma profile of the wine. No significant differences were observed in the volatile compounds production between the recombinants and their respective wild types, but some tendencies arose, especially for the monoterpene geraniol. The second objective of this study was to analyze the PGU1 gene and promoter from Saccharomyces paradoxus RO88 (a strain that exhibits high PG activity) and to compare it to those of S. cerevisiae S288C in order to identify differences that could potentially be responsible for the difference in their PG activities. Comparison of the gene sequences revealed several amino acid differences, one of which was in the peptide secretion signal. Analyses of the promoters also indicated some potentially important differences. Furthermore, S. cerevisiae strain VIN13, RO88 as well as two interspecies hybrids (all displaying varying PG activities) were compared under winemaking conditions. Clear differences were observed for the production of certain compounds. RO88 and the hybrids produced higher concentrations of certain volatile compounds, although they were not strong fermenters. Two recombinants, each containing a PGU1-overexpressing plasmid (one with the PGU1 gene from S. paradoxus and the other from S. cerevisiae), were also used in vinification to determine the effects of the different PGU1 gene on the aroma profile of the wine. Unfortunately, the plasmids were unstable and lost during the fermentation. Nevertheless, some tendencies were observed that indicated possible higher production of certain compounds by the recombinants compared to their wild types. This study identified that regulation of the PGU1 gene differs between strains with different genetic backgrounds. Certain differences were observed in the PGU1 gene and promoter sequences between S. cerevisiae and S. paradoxus that could potentially be the reason for the difference in their PG activities. From an oenological point of view, the presence of PGU1 in the genome of a fermenting strain tends to increase the aromatic potential of wine. These results provide a good platform for further studies on the PGU1 gene.
Analysis of Saccharomyces cerevisiae deletion mutants displaying a modified carbon flux under wine fermentative conditions
(Stellenbosch : University of Stellenbosch, 2009-03) Madlanga, Ncedile Hamilton; Bauer, Florian; Bosch, S.; University of Stellenbosch. Faculty of Agrisciences. Dept. of Viticulture and Oenology. Institute for Wine Biotechnology.
Saccharomyces cerevisiae has been used for millennia for the leavening of dough and in the production of alcoholic beverages such as beer and wine. More recently, it is being used as cell factories for the production of important pharmaceutical products. S. cerevisiae has also been extensively used as a model organism for studying many genetic and biochemical processes within the eukaryotic cell. Since the completion of a yeast genome sequence, many functional analysis projects have emerged with the aim of elucidating the functions of the unidentified genes revealed by the genome sequence. One of the most relevant approaches consisted in the construction of a collection of mutants deficient in all single genes, either in a haploid background for non-essential genes, or as heterozygous diploids for essential genes. This collection of strains can be subjected to phenotypic screens that might reveal the function of unknown genes or add to our understanding of already annotated genes. While this approach is promising, it also bears some limitations. For instance, many mutants have no overt phenotypes and some phenotypes do not obviously showcase the function of the encoded protein. In this study, S. cerevisiae strains with single deletions of genes involved in pyruvate metabolism were selected from the Euroscarf deletion library. Pyruvate is a central intermediate of glycolysis, and pyruvate metabolism largely defines the general distribution of carbon flux in the cell. These mutants were screened for modified fermentation kinetics or modified carbon flux under wine fermentative conditions, an environment that had not been previously used for the analysis of these mutants. A strain disrupted in the PDA1 gene, which encodes the E1α subunit of the pyruvate dehydrogenase showed a significant change in phenotype when grown in wine fermentative conditions. In particular, the mutant displayed a prolonged lag phase, but upon entering exponential growth, fermented significantly faster than the wild type strain and completed alcoholic fermentation in a shorter period of time. This phenotype could be of significant industrial interest. The mutant phenotype was further investigated through disruption of the gene in the same as well as in different genetic backgrounds, and through complementation of the PDA1 deletion with a plasmid-born wild type copy. The data show that the PDA1 gene disruption is not solely responsible for the observed phenotypes under wine fermentative conditions. We therefore propose that secondary mutations have contributed to the mutant phenotype. This study shows that phenotypes attributed to a specific gene in mutants of the Euroscarf library should always be confirmed before performing consequent experiments and drawing significant conclusions.
An anatomical and experimental study on changes induced by Meloidogyne hapla Chitwood, 1949 in Vitis roots
(Stellenbosch : Stellenbosch University, 1971) Joubert, D. J. (Daniel Jakobus); Orffer, C. J.; De Vos, M. P.; Stellenbosch University. Faculty of AgriSciences. Dept. of Viticulture and Oenology and Institute for Wine Biotechnology .
ENGLISH ABSTRACT: The object of this anatomical study was to collect scientific data on the effect of Metoidogyne hapta Chitwood, 1949, on the roots of the following grapevine cultivars viz: Vitis vinifePa L. cvs. Steen and White French and the root-stocks, Jacquez, 1202 C, 99 R, Salt.Creek and Dogridge. These cultivars differed widely in their resistance to M. hapta attacks. In the roots of Steen, White French, Jacquez and 1202 C the formation of multinucleate syncytia by the destruction of the walls of groups of cells often occurred. In Salt Creek, Dogridge and 99 R roots, syncytia were observed in the stele only. The formation o,f abnormal xylem as a result of nematodal activities was a common occurrence. In the roots of these latter three cultivars, M. hapta could not complete its life cycle. Salt Creek, Dogridge, 99 R and often Steen formed a wound periderm which prevented the nematodes from reaching the xylem. Histological changes were often induced in advance of the invading nematodes.
Anatomical responses to cytokinins of abscised grapevine shoot apices cultured in vitro
(South African Society for Enology and Viticulture, 1987) Goussard, P. G.
Responses of excised shoot apices of V. vinifera L. cv. Chenin blanc to different cytokinin treatments were studied at various intervals (days) after the start of in vitro culture, using light and scanning electron microscopy. Results clearly indicated that in vitro produced shoots were of axillary origin. Shoot clusters were produced by the enhanced release of axillary meristems from apical dominance, due to the application of 6-benzylaminopurine (BAP) singly as well as in combination with zeatin riboside (ZR). Axillary meristems on these axillary shoots were subsequently released from apical dominance, thus giving rise to shoot clusters of high densities. Shoot clusters induced by ZR alone were less dense, probably due to an initial delay in elongation of axillary meristems nearest to the main apical meristem of the shoot. However, elongation of axillary meristems lower down the axes proceeded strongly in the presence of ZR. Application of BAP resulted in more pronounced release of axillary meristems from apical dominance than with ZR.
Aspects of sucrose metabolism in transgenic tobacco
(Stellenbosch : Stellenbosch University, 2004-12) Champanis, Reinette; Vivier, Melane A.; Botha, F. C.; Pretorius, I. S.; Stellenbosch University. Faculty of AgriSciences. Dept. of Viticulture and Oenology. Institute for Wine Biotechnology.
ENGLISH ABSTRACT: In most plants the efficiency of sucrose production and the systemic distribution thereof are the major determinants of growth, development and yield. The factors governing sugar partitioning co-ordinate its distribution in response to intrinsic and environmental signals. These factors include sugar transporters and invertases as well as metabolites, including sucrose and glucose, which function as signalling molecules to modulate gene expression. The genetic transformation of plants and the subsequent development of transgenic lines with disturbed sugar metabolism have made an unprecedented impact on the study of sugar translocation and -partitioning. For instance, the transformation of plants with a yeast-derived invertase targeted to different subcellular compartments has led to the elucidation of several key aspects of sugar metabolism, including phloem loading mechanisms, the regulation of photosynthesis by sugars, the importance of sugar-metabolism compartmentation with regards to sucrose biosynthesis, storage and distribution, as well as the role of cell-wall invertase in phloem unloading and sink strength. In this study, a similar strategy of transgenic plant analysis was employed to expand our insight into the regulation of sugar partitioning. The yeast-invertase Suc2 gene, from Saccharomyces cere visiae , was overexpressed in either the cytosol, vacuole or apoplast of transgenic tobacco plants. These transgenic lines displayed varying increases in invertase activity, altered sugar levels and consequently disturbed sink-source interactions and sugar partitioning. Transgenic lines overproducing the yeast-derived invertase in either the vacuole (Vac-Inv) or apoplast (Apo-Inv) were utilised to analyse the effect of the altered sugar levels in sink and source organs on the expression of sugar transporters, as well as the endogenous cell wall invertase and inhibitors in these plants. Transcript levels of the sucrose transporter NtSUT1 and hexose transporter NtMST1 encoding genes increased significantly in the source leaves and roots of Vac-Inv lines, whereas increased NtMst1 transcript levels were also detected in the roots of Apo-Inv lines. The increased mRNA levels could be correlated to the altered invertase activities and sugar levels in these tissues. It is concluded that NtSUT1 and NtMST1 are differentially regulated by sucrose and/or hexose content on a transcriptional level. Furthermore, the regulatory effect of the altered sugar levels on transporter expression depended on the subcellular compartment in which the yeast invertase was expressed. It would seem that the subcellular compartmentation of sugar metabolism is also fundamental to the regulation of sugar partitioning. The transcription levels of the endogenous cell wall invertase (CWt) and cell wall invertase inhibitor (Cwi-Inh) genes were examined in the various tissues of Apo-Inv and Vac-Inv lines at both the vegetative and flowering growth stages. In comparison with the control lines, the various tissues of the Apo-Inv and Vac-Inv lines displayed altered Cwi and Cwi-Inh expression levels, depending on the sink-source status and growth stage. However, no obvious correlation between the Cwi and Cwi-Inh expression levels and soluble sugar content of these tissues was found. It is suggested that the post-transcriptional and post-translation control of these proteins by sugars might play an important role in their regulation. Analysis of the Cwi:Cwi-lnh mRNA ratio and growth observations of the various tissues of control as well as Apo-Inv and Vac-Inv lines indicated that this transcription ratio could be an accurate indicator of the sink strength of sink organs. In addition, the influence of sink-source interactions on sugar partitioning was investigated. Reciprocal grafting between Apo-Inv and control lines resulted in scions with an altered sucrose metabolism in either the sink or source organs. These scions were subjected to biomass distribution, soluble sugar quantification and C4C]- radiolabelling experiments. The latter revealed an unaltered state of sugar partitioning from the above-ground tissues of the Apo/GUS scions and a significant shift in sugar partitioning towards the roots of the GUS/Apo scions in comparison to the control GUS/GUS scions. Phenotypic changes, opposite to those observed in Apo-Inv lines expressing the heterologous invertase in both sink and source organs, could initially be observed in the GUS/Apo and Apo/GUS scions. However, no significant differences in phenotype or biomass distribution could be observed between the mature GUS/Apo, Apo/GUS and GUS/GUS scions seven weeks postgrafting. This inconsistency between phenotype and sugar partitioning might be explained by an increase in the respiration rate of the tissues as supported by the soluble sugar content. These results highlight the complexity and adaptability of sucrose metabolism and sugar partitioning. In addition, it confirms that sugar partitioning can be modulated by sink-source interactions and emphasise the importance of invertases in the regulation of sugar partitioning through its ability to alter sink strength. This study forms part of the rapidly expanding initiative to unravel the control mechanisms of sugar partitioning. The results obtained in this study confirmed again that the introduction and expression of a single heterologous gene in transgenic plants could provide significant insight into the regulation of this process. It was shown here that the expression of sugar transporters is closely regulated by sugar levels and therefore fulfils a vital function in sugar sensing and consequently the regulation of sugar partitioning. The data presented in this study also demonstrated the intricate and flexible nature of the relationship that exists between sugar metabolism, partitioning and growth phenomena.
Assessing the compatibility and aroma production of NT 202 Co-Inoculant with different wine yeasts and additives
(Stellenbosch : Stellenbosch University, 2013-03) Scholtz, Marene; Du Toit, Maret; Lerm, Elda; Stellenbosch University. Faculty of AgriSciences. Dept. of Viticulture and Oenology.
ENGLISH ABSTRACT: The influence of malolactic fermentation (MLF) in most red and some white wines is one of many factors that determine or influence wine quality, because it affects the flavour and sensory profile of wine. This process is a decarboxylation process conducted by lactic acid bacteria (LAB) such as Oenococcus, Lactobacillus, Pediococcus and Leuconostoc. Mostly Oenococcus oeni, but recently also Lactobacillus plantarum is used in commercial starter cultures and also the first mixed MLF starter culture (NT 202 Co-Inoculant) was commercialized in 2011. The reason for the predominant use of O. oeni and recently L. plantarum is due to their tolerance to the harsh wine environment. Malolactic fermentation leads to a decrease in acidity and an increase in pH that leaves the wine with a softer mouthfeel. Another reason to conduct MLF is the improvement of microbial stability by the removal of malic acid as carbon source. Research focus has recently shifted to the ability of LAB and MLF as well as the interaction of LAB with yeast to alter the wine aroma profile via the modification and/or production of certain aroma compounds. The main goal of this study was to assess the impact of yeast and nutrient addition on the ability of the NT 202 Co-Inoculant to conduct MLF during co-inoculation and to evaluate the aroma compound production in the final wine. The first aim was to evaluate the impact of different red and white wine yeast strains on the ability of the NT 202 Co-Inoculant to conduct MLF during co-inoculation in Chardonnay, Merlot and Shiraz. Malolactic fermentation was unsuccessful in the Chardonnay due to a low pH, but successful in Merlot and Shiraz. Based on the malic acid degradation ability of the NT 202 Co- Inoculant, the yeasts were grouped into three categories: inhibitory, neutral or stimulatory towards MLF. Co-inoculated MLF showed a clear decrease in total fermentation time while yeast strains such as WE 372 and Exotics showed positive compatibility with the NT 202 Co- Inoculant. The impact of the yeast-bacterial combinations on the aroma compound production in the final wine was evaluated. Co-inoculated MLF showed positive aroma changes in the red wines with a general increase in total esters (associated with fruity characters in wine) especially ethyl lactate and diethyl succinate that also contribute to the mouthfeel of the wine. Production of esters, volatile fatty acids and higher alcohols seemed to depend on the yeastand LAB strain used. The NT 202 Co-Inoculant contributed to the monoterpenes produced and MLF led to increased concentrations of diacetyl and acetoin, which are associated with buttery characters in wine. The second aim of this study was to evaluate the impact of wine additives (used during coinoculation) such as yeast- and bacterial nutrients, clarifying- and detoxifying agents on the ability of the NT 202 Co-Inoculant to conduct MLF and to assess their impact on the aroma compound production in the final wine. No negative or positive impact on the malic acid degradation of the NT 202 Co-Inoculant or the resulting aroma compound production was observed for the different wine additives used in this study. The results generated from this study showed that the selection of yeast strains is important as it will influence both the fermentation duration and final wine aroma.
Assessment of the possible interactions between soil and plant water status in a Vitis vinifera cv. Merlot vineyard
(Stellenbosch : Stellenbosch University, 2014-12) Van Zyl, Albertus J.; Strever, Albert E.; Stellenbosch University. Faculty of AgriSciences. Dept. of Viticulture and Oenology.
ENGLISH ABSTRACT: Irrigation scheduling decisions are based either on the direct measurement of soil water status (SWS) or on physiological measurements like plant water status (PWS). Soil based measurements are quick and easily automated, but the plant response for a particular quantity of soil moisture varies as a complex function of evaporative demand. A plant-based approach measures the plant stress response directly, but is an integration of environmental effects as well. In contrary to soil-based methods, plant based measurements can indicate when to irrigate, but not the quantity. Pre-dawn leaf water potential (ΨPD) is determined mostly by the soil moisture level, and can serve as a measure of static water stress in plants and an index of bulk soil water availability or even as an estimate of soil water potential at the root surface. Therefore it should be possible to establish a link between SWS and PWS, but it is largely unknown how stable the link in a heterogeneous vineyard would be, and how the grapevine vegetative and reproductive response relates to this link. Plant water status plays a large role in determining vigour and yield of the plant. The levels of PWS are influenced by irrigation, but it was mostly affected by the season and vine location in the vineyard. More negative plant water potentials reduced vigour, but had a less pronounced effect on yield, while also reducing overall wine quality. Vigour variability in the vineyard was largely attributed to soil heterogeneity, which seemed to have a strong effect on SWS. SWS measurements were calibrated according to the observed variability, increasing the accuracy of measurements significantly. Soil water content values were used to establish a link between SWS and PWS. This link was determined over time using nine plots, consisting of rain-fed and irrigated regimes, in variable vigour areas. A non-linear relationship was found between ΨPD and percentage extraction of plant available water for rain-fed plots. When irrigation was applied, no correlation could be found. In this study, for Merlot in the Stellenbosch region, PWS differences affected vigour, and to a lesser extent yield, as well as wine quality. More negative plant water potentials reduced vigour more in high vigour areas than in lower vigour areas, which in turn led to unbalanced vegetative: reproductive ratios. This disturbed vine balance may have had a bigger impact on wine quality than PWS levels. Therefore a well-managed and balanced vine is able to withstand more stress, with less detrimental effects. This study also highlights the danger of limiting the assessment of soil and plant water status conditions to point measurements in vineyards with high levels of vigour variability.
Authentication of Sauvignon blanc wine in terms of added flavourings
(Stellenbosch : University of Stellenbosch, 2011-03) Treurnicht, Jeanne; Nieuwoudt, Helene; Van Rensburg, P.; University of Stellenbosch. Faculty of AgriSciences. Dept. of Viticulture and Oenology. Institute for Wine Biotechnology.
ENGLISH ABSTRACT: The varietal character of Sauvignon blanc wine is mostly defined by the balance between tropical and green vegetative flavour nuances. Grape derived methoxypyrazines are the main aroma contributors towards green vegetative flavours. Methoxypyrazines are heat and light sensitive. Due to warm climatic conditions in South Africa, methoxypyrazine levels decrease during grape ripening. The addition of food flavourings to Sauvignon blanc wine, a practice known as spiking, has occurred in the past to improve the green character of the wines. Adding flavourings to wine and selling the wine as natural certified wine is illegal in South Africa. Currently, adulterated Sauvignon blanc wines are identified using gas chromatography–mass spectrometry (GC-MS) and liquid chromatography–mass spectrometry (LC-MS) methods to quantify methoxypyrazines and compare levels to an established database. Although of high sensitivity, GC-MS and LCMS methods are costly and time consuming, therefore not optimal for routine screening of wines. Hence the need for the development of a fast and cost effective method for routine screening of large amounts of wines to identify adulteration. Small scale vinification practices were used to prepare experimental Sauvignon blanc wine. Flavourings were added to Sauvignon blanc grape juice before fermentation, during the preparation of experimental spiked wines. Control wines, containing no flavouring, were also prepared. Commercial wines were spiked after fermentation and bottling. Each wine was only spiked with a single flavouring. The flavourings added were the juice of homogenised fresh green peppers and commercially available flavourings for wine. The following commercial flavourings were used: green pepper, asparagus, grassy and tropical. The above mentioned wines were analyzed using Fourier transform infrared (FT-IR) spectroscopy, GC-MS, LC-MS and descriptive sensory analysis. The FT-IR techniques used were Fourier transform mid infrared (FT-MIR) transmission, FT-MIR attenuated reflection and Fourier transform near infrared (FT-NIR) reflection spectroscopy. The data was interpreted using the following multivariate statistical techniques: principal component analysis (PCA), partial least squares discrimination (PLS-D) and conformity testing. Multivariate models constructed from FT-MIR and FT-NIR data were able to discriminate between spiked and control wines. Sensory analysis results clearly showed differences between non-spiked wines and spiked wines with 3-isobutyl-2-methoxypyrazine concentrations 10 times higher than naturally occurring in wine. Differences between control and spiked wines with concentrations of 3-isobutyl-2-methoxypyrazine similar to concentrations naturally occurring in wines could not be detected to prove adulteration conducting sensory analysis. However, differences between control and spiked wines with levels of 3-isobutyl-2-methoxypyrazine similar to levels naturally occurring in wines could be detected using FT-IR data in conjunction with multivariate statistics. This study showed that, FT-IR spectroscopy in conjunction with multivariate statistical methods can be a possibility for the screening and identification of wines suspected of adulteration in terms of added flavourings. Descriptive sensory analysis also proved to be a potentially useful tool. However screening and training of potential panel members are time consuming.
Bacterial diversity of Cabernet Sauvignon must from different locations and the dynamics during wine fermentation
(Stellenbosch : Stellenbosch University, 2022-04) Mathidza, Bill; Setati, Mathabatha Evodia; Du Plessis, Heinrich; Stellenbosch University. Faculty of AgriSciences. Dept. of Viticulture and Oenology.
ENGLISH ABSTRACT: Wine grapes harbour a microbiota that drives wine fermentations that may contribute to the chemical fingerprint of finished wines. The bacterial communities on grapes, in particular lactic acid bacteria (LAB) conduct malolactic fermentation (MLF), which modifies the acidity, flavour and microbial stability of wine. This study aimed to investigate the bacterial diversity on Vitis vinifera L. cv Cabernet Sauvignon in three vineyards (VIN-A, VIN-B and VIN-C), situated in different areas of the Stellenbosch wine district during 2019 and 2020 vintages. The Automated Ribosomal Intergenic Spacer Analysis (ARISA) was used to evaluate the community fingerprint of grape must. Bacterial population dynamics and diversity were determined in grape must and throughout the wine fermentation by cultivating bacteria on nutrient media and using Polymerase Chain Reaction and sequence analysis of the 16S region. Followed by the characterisation of a selection of Lactiplantibacillus plantarum and Oenococcus oeni isolates from the 2019 and 2020 vintages, which were subjected to Random Amplified Polymorphic DNA (RAPD) typing to generate genetic profiles, which were compared to determine their recurrence in the various vineyards. Chemical composition (pH, malic acid and sugar) of the grape must from each vineyard were different for both vintages. The fermentations differed between the vineyards, the wines from VIN- A was able to complete the MLF in 2019, while other vineyards presented stuck MLF. Using ARISA, 117 and 116 peaks were detected in 2019 and 2020, respectively. Each peak was considered as an operational taxonomic unit (OTU). The data showed some overlap of the OTUs in grape must from different vineyards. Thirteen bacterial OTUs in 2019 and 8 peaks in 2020 were detected in all three vineyards, whereas the majority of the OTUs were vineyard specific. Analysis of similarities (ANOSIM) of the OTU data showed notable differences in the bacterial communities between vintages. The viable counts of the grape must differed between the vintages. In 2019, the total bacterial population density in grape must ranged between 103 and 105 colony forming units per millilitres (CFU/mL), while in 2020, the bacterial population density ranged between 103 and 104 CFU/mL. A total of 360 bacterial isolates including both LAB and acetic acid bacteria (AAB) were obtained from grape must and different stages of fermentation from all vineyards during both vintages. The bacterial diversity differed between the vineyards and over the vintages. Five bacterial species were detected in grape must from VIN-B and VIN-C and 3 species in VIN-A in 2019, whereas 2020 presented higher bacterial diversity and 6, 11 and 6 different species were identified in VIN- A, VIN-B and VIN-C respectively. L. plantarum was found in grape must from all vineyards, accounting for more than 50% of the total population. O. oeni was detected in grape must of both 2019 and 2020 vintages from VIN-B and VIN-C, where it accounted for 4% of the total population in 2019. In general, the overlap of common species such as Apilactobacillus kunkeei and Acetobacter malorum was observed in wine from different vineyards. Minor unique species were isolated and clearly differed between the three vineyards. In addition, L. plantarum ISP20_9 and O. oeni ISO20_1 were the only isolates that were recurring in both 2019 and 2020 vintages. The L. plantarum and O. oeni strains showed different patterns of malic acid degradation within 7 days, indicating strain differences.
Basic in-mouth attribute evaluation : a comparison of two panels
(MDPI, 2018-12-21) Mihnea, Mihaela; Aleixandre-Tudo, Jose Luis; Kidd, Martin; Du Toit, Wessel
Astringency is often difficult to evaluate accurately in wine because of its complexity. This accuracy can improve through training sessions, but it can be time-consuming and expensive. A way to reduce these costs can be the use of wine experts, who are known to be reliable evaluators. Therefore, the aim of this work was to compare the sensory results and the panel performance obtained using trained panelists versus wine experts (winemakers). Judges evaluated twelve red wines for in-mouth basic perception (sweet, sour, bitter, astringent, and burning sensation) following the same tasting protocol and with the samples being presented in two different tasting modalities. Panels’ performance and relationship between the chemical composition and the sensory perception were investigated. Both panels showed similar consistency and repeatability, and they were able to accurately measure the astringency of the wines. However, the significant correlations between sensory scores and chemical composition varied with the panel and the tasting modality. From our results, we could see that winemakers tended to discriminate better between the samples when the differences were very small.
Berry size variation of vitis vinifera l. Cv. Syrah : morphological dimensions, berry composition and wine quality
(South African Society for Enology and Viticulture, 2015) Melo, M. S.; Schultz, H. R.; Volschenk, C. G.; Hunter, J. J.
Berry size has always been a quality factor in wine production. In this study, Syrah grapes from a single vineyard were classified into different size groups according to diameter: small (< 13 mm), medium (13 < diameter < 14 mm) and large (> 14 mm). Smaller berries were present in the highest and larger berries in the lowest numbers. Size distributions were similar in both seasons (2010/2011 and 2011/2012). Berry physical characteristics (mass, volume and skin area) increased with size, showing the same tendency in both years. Positive correlations between berry mass, volume and skin area were found, whereas these variables were negatively related with berry number/kg grapes. Berry volume was negatively correlated with dry skin weight. Skin surface area/berry volume seems to be an indicator of the “dilution” effect associated with increasing size, as larger berries presented the lowest values. In 2012 the grapes were harvested at a higher soluble solid level than in the previous year; large-sized berries presented the lowest levels in both years. The whole-berry analysis of total anthocyanins showed a decrease in concentration and increase in content per berry, from smaller to larger berries. Small berries and the control (naturally occurring berry size mixture) showed a higher extractability of anthocyanins and phenolic compounds than the medium and large berries. Sensorially, wines from medium berries were more consistent over the two years, scoring higher than the rest. Berry sizes were related to wine style differences, and knowing the population of berry sizes in the vineyard close to harvest would offer a possibility to predict wine styles.
Berry tannin structure and phenolics evolution in cv. Cabernet Sauvignon (Vitis vinifera L.) : effect of light and temperature
(Stellenbosch : Stellenbosch University, 2015-12) Blancquaert, Erna; Deloire, A. J.; Oberholster, A.; Ricardo da Silva, J. M.; Stellenbosch University. Faculty of Agrisciences. Dept. of Viticulture and Oenology.
ENGLISH ABSTRACT: This study investigated grape flavonoid (proanthocyandins, flavonols and anthocyanins) accumulation and composition in grape seeds and skins from Cabernet Sauvignon (Vitis vinifera L.) under altered light intensities and temperatures, within the bunch zone in the Stellenbosch Wine of Origin District. Furthermore, the study examined the link between wine sensory properties and the harvest date. This study was conducted in 2010/2011 and 2011/2012 and comprised of two main treatments with altered bunch microclimates in both seasons: no lateral shoot or leaf removal in the bunch zone (STD) and leaf removal in the bunch zone (LRW). The leaves were removed just after flowering on the western side of the canopy at the fruiting zone level (±35–40 cm above the cordon). Furthermore, to study the effect of change in light quality and quantity on fruit growth and composition, supplementary treatments were applied. In 2010/2011, a UV-B reducing sheet was added on the western side of the canopy to the STD (STD-UV-B) and LRW (LRW-UV-B) treatments. During the 2011/2012 season two types of UV-B reducing sheets were installed on both sides of the canopy to exclude the effect that the row direction can have on grape development. The latter resulted in the following treatments: LR (-UV-B, 2xOp50) and LR (-UV-B, 2xUHI). The accumulated thermal time varied between the treatments and within a season. The 2010/2011 season had a higher accumulated thermal time than the 2011/2012 season. There was a significant difference in the photosynthetic active radiation (PAR) (p≤0.001) among the treatments indicating that the applied treatment were successful in creating variation in the amount of sunlight intercepted in the bunch zone. There were no significant differences in berry weights in 2010/2011, but a significant difference were observed in 2011/2012 (p≤0.001). Light and temperature had little effect on grape seed flavan-3-ol monomer and dimer concentration and content. Seed development after flowering potentially influenced light quality and quantity which impacted the seed number and affected flavan-3-ol concentration and content. Grape skin flavan-3-ol concentration and content differed significantly among the treatments in 2010/2011, but not in 2011/2012. Generally, the seasonal impact was larger than those of the different treatments on flavonoid concentration and content during ripening resulting in significant differences among the treatments at harvest in the 2010/2011 season. However, treatment did not have a significant effect on either concentration or composition of a compound. Grape seed and skin (terminal and extension subunit) composition were influenced by the seasonal impact, rather than the treatment in both seasons. Moreover, the structural characteristics such as the percentage galloylation (%G), percentage prodelphinidins (%P), mean degree of polymerization (mDP) and average molecular mass (avMM) were influenced by seasonal variation. The accumulation of flavonols was higher in the exposed treatments and low in treatments with UV-B reducing sheets. This indicates that flavonol synthesis is highly dependent on UV-B radiation. The accumulation of anthocyanins commenced at véraison and had two distinct patterns of accumulation in the respective seasons. The 2010/2011 season was characterised by a higher anthocyanin concentration and content compared to the cooler 2011/2012 season. Grapes were harvested sequentially based on the sugar loading model at the fresh fruit stage (four treatments) and pre-mature (control treatment only) in 2010/2011. In the 2011/2012 season four treatments were harvested at the mature fruit stage. Identified aromas in the respective wines corresponded to the sugar loading model profile. Wine tannin, anthocyanin and flavonol concentrations were the highest in the LRW treatment in 2011/2012. Mouthfeel properties (adhesiveness, coarse, puckery – in and after expectoration) were rated higher in the treatments which were exposed to high light intensities in both seasons. This research denotes the complex nature of flavonoid biosynthesis and composition. Therefore further research is needed to elucidate impact of the functioning of individual genes in the phenylproanoid and flavonoid pathways which have an influence on the final concentration, content and composition of flavonoids at harvest.

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