Browsing by Author "Pretorius, I. S."
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- ItemCarnitine biosynthesis in Neurospora crassa: Identification of a cDNA coding for ε-N-trimethyllysine hydroxylase and its functional expression in Saccharomyces cerevisiae(2002) Swiegers, J. H.; Vaz, F.M.; Pretorius, I. S.; Wanders, R. J. A; Bauer, FlorianThe biosynthesis of L-carnitine in eukaryotic organisms was first elucidated in the ascomycete Neurospora crassa. The first step of the pathway is catalysed by ε-N-trimethyllysine hydroxylase (TMLH), which converts ε-N-trimethyllysine into β-hydroxy-N-ε-trimethyllysine in a reaction dependent on α-ketoglutarate, Fe2+ and oxygen. Here we report on the cloning of the N. crassa TMLH cDNA and its functional expression in Saccharomyces cerevisiae. The TMLH cDNA contains an open reading frame of 1413 base pairs encoding a predicted polypeptide of 471 amino acids. The Michaelis-Menten constants of the heterologously expressed enzyme were determined for ε-N-trimethyllysine, α-ketoglutarate, Fe2+ and correspond to 0.33 mM, 133 μM and 46 μM, respectively. © 2002 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.
- ItemCarnitine-dependent metabolic activities in Saccharomyces cerevisiae: Three carnitine acetyltransferases are essential in a carnitine-dependent strain(2001) Swiegers, J. H.; Dippenaar, N.; Pretorius, I. S.; Bauer, FlorianL-Carnitine is required for the transfer of activated acyl-groups across intracellular membranes in eukaryotic organisms. In Saccharomyces cerevisiae, peroxisomal membranes are impermeable to acetyl-CoA, which is produced in the peroxisome when cells are grown on fatty acids as carbon source. In a reversible reaction catalysed by carnitine acetyltransferases (CATs), activated acetyl groups are transferred to carnitine to form acetylcarnitine which can be shuttled across membranes. Here we describe a mutant selection strategy that specifically selects for mutants affected in carnitine-dependent metabolic activities. Complementation of three of these mutants resulted in the cloning of three CAT encoding genes: CAT2, coding for the carnitine acetyltransferase associated with the peroxisomes and the mitochondria; YAT1, coding for the carnitine acetyltransferase, which is presumably associated with the outer mitochondrial membrane, and YER024w (YAT2), which encodes a third, previously unidentified carnitine acetyltransferase. The data also show that (a) L-carnitine and all three CATs are essential for growth on non-fermentable carbon sources in a strain with a disrupted CIT2 gene; (b) Yat2p contributes significantly to total CAT activity when cells are grown on ethanol; and that (c) the carnitine-dependent transfer of activated acetyl groups plays a more important role in cellular processes than previously realised. Copyright © 2001 John Wiley & Sons, Ltd.
- ItemCellular Differentiation in Response to Nutrient Availability: The Repressor of Meiosis, Rme1p, Positively Regulates Invasive Growth in Saccharomyces cerevisiae.(GENETICS, 428 EAST PRESTON ST, BALTIMORE, USA, MD, 21202, 2003) Van Dyk, D.; Hansson, G. R.; Pretorius, I. S.; Bauer, Florian
- ItemCharacteristics of Flo11-dependent flocculation in Saccharomyces cerevisiae(2005) Bayly, J. C.; Douglas, L. M.; Pretorius, I. S.; Bauer, Florian; Dranginis, A. M.The FLO11-encoded flocculin is required for a variety of important phenotypes in Saccharomyces cerevisiae, including flocculation, adhesion to agar and plastic, invasive growth, pseudohyphae formation and biofilm development. We present evidence that Flo11p belongs to the Flo1-type class of flocculins rather than to the NewFlo class. Both Flo1-type and NewFlo yeast flocculation are inhibited by mannose. NewFlo flocculation, however, is also inhibited by several other carbohydrates including glucose, maltose and sucrose. These differences have in at least one case been shown to reflect differences in the structure of the carbohydrate-binding site of the flocculins. We report that Flo11p-dependent flocculation is inhibited by mannose, but not by glucose, maltose or sucrose. Furthermore, Flo11p contains a peptide sequence highly similar to one that has been shown to characterise Flo1-type flocculins. Further characterisation of the properties of Flo11p-dependent flocculation revealed that it is dependent on calcium, occurs only at cell densities greater than 1 × 108 ml-1, and only occurs at acidic pH. © 2005 Federation of European Microbiological Societies. Published by Elsevier B.V. All rights reserved.
- ItemControlled expression of the dominant flocculation genes FLO1, FLO5, and FLO11 in Saccharomyces cerevisiae(2008) Govender, P.; Domingo, J. L.; Bester, M. C.; Pretorius, I. S.; Bauer, FlorianIn many industrial fermentation processes, the Saccharomyces cerevisiae yeast should ideally meet two partially conflicting demands. During fermentation, a high suspended yeast count is required to maintain a satisfactory rate of fermentation, while at completion, efficient settling is desired to enhance product clarification and recovery. In most fermentation industries, currently used starter cultures do not satisfy this ideal, probably because nonflocculent yeast strains were selected to avoid fermentation problems. In this paper, we assess molecular strategies to optimize the flocculation behavior of S. cerevisiae. For this purpose, the chromosomal copies of three dominant flocculation genes, FLO1, FLO5, and FLO11, of the haploid nonflocculent, noninvasive, and non-flor-forming S. cerevisiae FY23 strain were placed under the transcriptional control of the promoters of the ADH2 and HSP30 genes. All six promoter-gene combinations resulted in specific flocculation behaviors in terms of timing and intensity. The strategy resulted in stable expression patterns providing a platform for the direct comparison and assessment of the specific impact of the expression of individual dominant FLO genes with regard to cell wall characteristics, such as hydrophobicity, biofilm formation, and substrate adhesion properties. The data also clearly demonstrate that the flocculation behavior of yeast strains can be tightly controlled and fine-tuned to satisfy specific industrial requirements. Copyright © 2008, American Society for Microbiology. All Rights Reserved.
- ItemConverting plant biomass to fuels and commodity chemicals in South Africa : a third chapter?(Academy of Science for South Africa, 2003) Lynd, L. R.; Von Blottnltz, H.; Tait, B.; De Boer, J.; Pretorius, I. S.; Rumbold, K.; Van Zyl, W. H.THERE HAVE BEEN TWO DISTINCT CHAPTERS in the history of converting cellulosic biomass to fuels and commodity chemicals in South Africa. The first chapter, from the late 1970s to the early 1990s, involved some of the most active research and development efforts of their kind anywhere in the world. Thereafter, during the second chapter, there has been very little activity in the field in South Africa while there has been an unprecedented awakening to the potential of biomass conversion elsewhere. This paper considers the rationale and possible benefits of a potential third chapter based on a revitalized effort on biomass conversion in South Africa. Such an enterprise would build on the country's large biomass production potential, strong technical capability in yeast biotechnology, a well-developed research and development infrastructure in biological processing, and expertise derived from the largest non-petroleum hydrocarbon processing industry in the world. Substantial societal benefits could be realized that address critically important national needs, including the utilization of sustainable resources, industrial development, and improved balance of payments. Moreover, establishing a modern biomass processing industry in South Africa appears to represent one of the largest potential sources of rural employment identified to date. We propose steps to realizing these benefits.
- ItemCorrelation between glucose/fructose discrepancy and hexokinase kinetic properties in different Saccharomyces cerevisiae wine yeast strains(2008) Berthels, N. J.; Cordero Otero, R. R.; Bauer, Florian; Pretorius, I. S.; Thevelein, J. M.Grape juice contains about equal amounts of glucose and fructose, but wine strains of Saccharomyces cerevisiae ferment glucose slightly faster than fructose, leading to fructose concentrations that exceed glucose concentrations in the fermenting must. A high fructose/glucose ratio may contribute to sluggish and stuck fermentations, a major problem in the global wine industry. We evaluated wine yeast strains with different glucose and fructose consumption rates to show that a lower glucose preference correlates with a higher fructose/glucose phosphorylation ratio in cell extracts and a lower K m for both sugars. Hxk1 has a threefold higher V max with fructose than with glucose, whereas Hxk2 has only a slightly higher V max with glucose than with fructose. Overexpression of HXK1 in a laboratory strain of S. cerevisiae (W303-1A) accelerated fructose consumption more than glucose consumption, but overexpression in a wine yeast strain (VIN13) reduced fructose consumption less than glucose consumption. Results with laboratory strains expressing a single kinase showed that total hexokinase activity is inversely correlated with the glucose/fructose (G/F) discrepancy. The latter has been defined as the difference between the rate of glucose and fructose fermentation. We conclude that the G/F discrepancy in wine yeast strains correlates with the kinetic properties of hexokinase-mediated sugar phosphorylation. A higher fructose/glucose phosphorylation ratio and a lower K m might serve as markers in selection and breeding of wine yeast strains with a lower tendency for sluggish fructose fermentation. © 2007 Springer-Verlag.
- ItemDiscrepancy in glucose and fructose utilisation during fermentation by Saccharomyces cerevisiae wine yeast strains(2004) Berthels, N. J.; Cordero Otero, R. R.; Bauer, Florian; Thevelein, J. M.; Pretorius, I. S.While unfermented grape must contains approximately equal amounts of the two hexoses glucose and fructose, wine producers worldwide often have to contend with high residual fructose levels (>2 gl-1) that may account for undesirable sweetness in finished dry wine. Here, we investigate the fermentation kinetics of glucose and fructose and the influence of certain environmental parameters on hexose utilisation by wine yeast. Seventeen Saccharomyces cerevisiae strains, including commercial wine yeast strains, were evaluated in laboratory-scale wine fermentations using natural Colombard grape must that contained similar amounts of glucose and fructose (approximately 110 gl-1 each). All strains showed preference for glucose, but to varying degrees. The discrepancy between glucose and fructose utilisation increased during the course of fermentation in a strain-dependent manner. We ranked the S. cerevisiae strains according to their rate of increase in GF discrepancy and we showed that this rate of increase is not correlated with the fermentation capacity of the strains. We also investigated the effect of ethanol and nitrogen addition on hexose utilisation during wine fermentation in both natural and synthetic grape must. Addition of ethanol had a stronger inhibitory effect on fructose than on glucose utilisation. Supplementation of must with assimilable nitrogen stimulated fructose utilisation more than glucose utilisation. These results show that the discrepancy between glucose and fructose utilisation during fermentation is not a fixed parameter but is dependent on the inherent properties of the yeast strain and on the external conditions. © 2004 Published by Elsevier B.V. on behalf of the Federation of European Microbiological Societies.
- ItemDivergent regulation of the evolutionarily closely related promoters of the Saccharomyces cerevisiae STA2 and MUC1 genes(1999) Gagiano, M.; Van Dyk, D.; Bauer, Florian; Lambrechts, M. G.; Pretorius, I. S.The 5' upstream regions of the Saccharomyces cerevisiae glucoamylase- encoding genes STA1 to -3 and of the MUC1 (or FLO11) gene, which is critical for pseudohyphal development, invasive growth, and flocculation, are almost identical, and the genes are coregulated to a large extent. Besides representing the largest yeast promoters identified to date, these regions are of particular interest from both a functional and an evolutionary point of view. Transcription of the genes indeed seems to be dependent on numerous transcription factors which integrate the information of a complex network of signaling pathways, while the very limited sequence differences between them should allow the study of promoter evolution on a molecular level. To investigate the transcriptional regulation, we compared the transcription levels conferred by the STA2 and MUC1 promoters under various growth conditions. Our data show that transcription of both genes responded similarly to most environmental signals but also indicated significant divergence in some aspects. We identified distinct areas within the promoters that show specific responses to the activating effect of Flo8p, Msn1p (or Mss10p, Fup1p, or Phd2p), and Mss11p as well as to carbon catabolite repression. We also identified the STA10 repressive effect as the absence of Flo8p, a transcriptional activator of flocculation genes in S. cerevisiae.
- ItemEnzymes in winemaking : harnessing natural catalysts for efficient biotransformations(South African Society for Enology and Viticulture, 2000) Van Rensburg, P.; Pretorius, I. S.Enzymes play a definitive role in the ancient and complex process of winemaking. From a scientific and technical point of view, wine can be seen as the product of enzymatic transformation of grape juice. From the pre-fermentation stage, through fermentation, post-fermentation and aging, enzymes are the major driving forces catalysing various biotransformation reactions. These biocatalysts originate not only from the grape itself but also from yeasts and other microbes (fungi and bacteria) associated with vineyards and wine cellars. Through better understanding of these enzymatic activities, winemakers have come to learn how to control the unwanted enzymes while optimising the desired activities. Today, winemakers reinforce and extend the action of these endogenous enzymes by the judicious application of an ever-increasing spectrum of commercial enzyme preparations. These enzyme preparations are applied to winemaking with the aims of improving the clarification and processing of wine, releasing varietal aromas from precursor compounds, reducing ethyl carbamate formation and lowering alcohol levels. This review article summarises the most important enzymes applied to winemaking, the nature and structure of their substrates, and the reactions catalysed by these enzymes. This paper also reviews the limitations of the endogenous enzymes derived from grapes and microbes present in must and wine, along with the effects of commercial enzyme preparations on process technology and the quality of the final product. Prospects of developing wine yeast strains expressing tailored enzymes are also highlighted.
- ItemEvaluation of principal component analysis as a tool to design calibration sets for glycerol quantification in wine with Fourier transform infrared spectroscopy.(2007) Nieuwoudt, Helene; Prior, B. A.; Pretorius, I. S.; Manley, M.; Bauer, Florian
- ItemFlocculation, pseudohyphal development and invasive growth in commercial wine yeast strains(South African Society for Enology and Viticulture, 1998) Carstens, Elsa; Lambrechts, M. G.; Pretorius, I. S.Flocculation of Saccharomyces cerevisiae cells at the end of alcoholic fermentation is an important phenomenon in winemaking, especially in the production of bottle-fermented sparkling wine. Most wine yeast strains do not flocculate during the fermentation process and it is unknown whether they contain the necessary genes to flocculate and whether these genes are expressed adequately under wine-making conditions. These genes include the FLO1 flocculin gene which is one of the most important genes to confer the ability of yeast cells to flocculate and the MUC1 gene (subsequently also cloned as FLO11) encoding a mucin-Iike protein which was previously shown not only to play a key role in pseudohyphal development and invasive growth, but also to be involved in flocculation in S. cerevisiae. Together with MUC1, the involvement of FL08 (encoding a transcriptional activator of FLO1) and TUPI in flocculation, pseudohyphal development and invasive growth indicates that these processes might somehow be linked. Therefore, in order to construct wine yeast strains that are able to flocculate, 25 commercial wine yeast strains were investigated for their ability to flocculate, form pseudohyphae and invade solid media. Twenty-one of these strains were able to penetrate into agar media and different degrees of pseudohyphal and invasive growth were observed. The average length of cells and pseudohyphae and the efficiency of invasive growth varied among these strains. Two of the strains are known to flocculate in wine, while three other strains could be induced to aggregate to a limited degree in glycerol-ethanol medium. Southern blot analyses revealed the presence of homologous DNA sequences in all of the 25 strains using DNA fragments of FL08, MSS1O and MSS11 (encoding transcriptional activators of MUC1), FLO1 and MUC1 as probes. Using Northern blot analysis, FLO1 transcripts were detected in only one of the strains that showed constitutive flocculation in all the growth media tested. MUCJ transcripts of varying sizes could be detected in most of the strains. From these results it is clear that MUC1 does not primarily confer the phenotype of flocculation and that FLO1 (flocculation) and MUC1 (pseudohyphal differentiation, invasive growth and flocculation) are not co-regulated. We therefore suggest that MUC1, as opposed to FLO11, be retained as the most appropriate designation of this gene encoding the S. cerevisiae mucin-like protein.
- ItemGenetic improvement of grapevine : tailoring grape varieties for the third millennium(South African Society of Enology and Viticulture, 2000) Vivier, M. A.; Pretorius, I. S.The remarkable propagative aptitute of grapevine is one of the key factors contributing to its success as a cultivated species and to the spread of the domesticated grapevine, establishing it as one of the most important fruit species worldwide. Today there are some 8 million hectares of vineyards across the world. It is therefore titting that the successful implementation of the powerful technology of gene manipulation in grapevine is to a large extent reliant on this regenerative ability. Currently, several varieties of grapevines have been successfully genetically transformed, largely by employing somatic embryogenesis to generate highly regenerative target material. Especially attractive in the wine industry is the possibility of improving grapevine varieties by the addition of genes that confer useful traits, such as resistances against biotic and abiotic factors and manipulation of certain metabolic functions. In principle, gene transfer technology allows for the directed manipulation of a specific trait without altering the characteristic nature of the cultivar, permitting the improvement of the traditional cultivars while maintaining their established varietal characteristics. For the most part, targeted traits currently include disease resistance and improved berry quality. The promise of this technology is threatened by worldwide resistance to genetically modified organisms, and in the wine industry by complications surrounding the property rights and naming of transgenic vines. If it is not possible to maintain the varietal name when a transgenic vine has the same properties as the original well known variety, the significant advantages of gene technology over traditional breeding programmes are to a large extent lost. If these and other complications can be overcome, the integration of this powerful technology with traditional breeding programmes, and with other initiatives such as the study of the grapevine genome, will ensure a new era in the cultivation of this ancient species.
- ItemDie genetiese verbetering van wyndruifkultivars en wyngisrasse vir 'n markgerigte wynbedryf : nuwe benaderings tot die oeroue kuns van wynbereiding(AOSIS OpenJournals, 2003) Pretorius, I. S.The widening gap between wine production and wine consumption, the shift of consumer preferences away from basic commodity wine to top quality wine, and the gruelling competition brought about by economic globalisation call for a total revolution in the magical world of wine. In the process of transforming the wine industry from a production-driven industry to a market-orientated enterprise, there is an increasing dependence on, amongst others, biotechnological innovation to launch the wine industry with a quantum leap across the formidable market challenges of the 21st century. Market-orientated designer grape cultivars and wine yeast strains are currently being genetically programmed with surgical precision for the cost-competitive production of high quality grapes and wine with relatively minimal resource inputs and a low environmental impact. With regard to Grapevine Biotechnology, this entails the establishment of stress tolerant and disease resistant varieties of Vitis vinifera with increased productivity, efficiency, sustainability and environmental friendliness, especially regarding improved pest and disease control, water use efficiency and grape quality. With regard to Wine Yeast Biotechnology, the emphasis is on the development of Saccharomyces cerevisiae strains with improved fermentation, processing and biopreservation abilities, and capacities for an increase in the wholesomeness and sensory quality of wine. The successful commercialisation of transgenic grape cultivars and wine yeasts depends on a number of scientific, technical, safety, ethical, legal, economic and marketing factors, and it therefore will be unwise to entertain high expectations in the short term. However, in the light of the phenomenal potential advantages of tailor-made grape varieties and yeast strains, it would be equally self-destructive in the long term if this strategically important “life insurance policy” is not taken out by the wine industry. This overview highlights the most important examples of the way in which V. vinifera grape varieties and S. cerevisiae wine yeast strains are currently being designed with surgical precision on the basis of market demand for the cost-effective, sustainable and environmentally friendly production of healthy, top quality grapes and wine.
- ItemGeographic distribution and evaluation of saccharomyces cerevisiae strains isolated from vineyards in the warmer, Inland Regions of the Western Cape in South Africa(South African Society for Enology and Viticulture, 2000) Khan, W.; Augustyn, O. P. H.; Van der Westhuizen, T. J.; Lambrechts, M. G.; Pretorius, I. S.The aim of this study was to examine the geographic distribution of Saccharomyces cerevisiae strains indigenous to 19 sites in the warmer, inland regions of the Western Cape in South Africa. These strains were compared to those isolated previously from the cooler, coastal regions of the same province by subjecting both sets of organisms to the same characterisation procedures. Thirty isolates per sampling site were isolated and the S. cerevisiae strains subjected to the following characterisation procedures; karyotyping using pulse field gel electrophoresis (CHEF), randomly amplified polymorphic DNA, the polymerase chain reaction technique (RAPD-PCR), sugar fermentation ability, flocculation ability, stress resistance/response and extracellular enzyme activity. When considering biodiversity per sampling site, CHEF karyotypes indicated the recovery of 30 S. cerevisiae strains. This number was reduced to 21 when comparing banding patterns over sites. Addition of RAPD-PCR data expanded the number of unique strains to 29. Subsequent consideration of sugar fermentation data indicated that one of the strians with exactly equivalent CHEF and RAPD-PCR patterns was in fact galactose positive while the other was galactose negative. These data clearly indicate that characterisation of yeast strains by application of a single technique is not a sound practice. None of the S. cerevisiae strains isolated in this study occurred in the coastal regions. In addition, each site sampled in this study had its own unique collection of wine yeast strains and no strain common to all sites in the study region was found. Survival mechanisms of S. cerevisiae are obscure. Although we found that many of the isolated strains could grow invasively/form pseudohyphae and that these abilities could therefore contribute to the organism's overwintering ability, other mechanisms must also be involved.
- ItemGeographical distribution of indigenous saccharomyces cerevisiae strains isolated from vineyards in the coastal regions of the Western Cape in South Africa(South African Society for Enology and Viticulture, 2000) Van der Westhuizen, T. J.; Augustyn, O. P. H.; Pretorius, I. S.Notwithstanding numerous studies on the yeast biota of grapes and grape must, the origin of the primary wine yeast Saccharomyces cerevisiae has been rather controversial. One school of thought claims that the primary source of S. cerevisiae is the vineyard, whereas another believes that ecological evidence points to a strict association with artificial, man-made environments such as wineries and fermentation plants. One of the main thrusts of these kinds of investigations is to understand the succession of yeasts during fermentation of wine and to determine the actual contribution of indigenous strains of S. cerevisiae and wild yeast species to the overall sensorial quality of the end product, even in guided fermentations using selected S. cerevisiae starter cultures. There is increasing interest within the wine community in the use of indigenous strains of S. cerevisiae and mixed starter cultures, tailored to reflect the characteristics of a given region. Against this background we have launched a comprehensive and long overdue biogeographical survey systematically cataloging yeasts in different climatic zones of the 350-year-old wine-producing regions of the Western Cape. The present paper represents the first phase of this programme aimed at preserving and exploiting the hidden oenological potential of the untapped yeast biodiversity in South Africa's primary grape-growing areas. Grapes were aseptically harvested from 13 sites in five areas in the coastal regions of the Western Cape. After fermentation, 30 yeast colonies per sample were isolated and examined for the presence of S. cerevisiae. Five sampling sites yielded no S. cerevisiae. CHEF-DNA analysis revealed the presence of 46 unique karyotypes in eight of the remaining sites. No dominant strain was identified and each site had its own unique collection of strains. The number of strains per site varied from two to 15. Only in four cases did one strain appear at two sites, while only one instance of a strain occurring at three sites was recorded. All sites contained killer and sensitive strains; however, killer strains did not always dominate. Commercial strains were recovered from three sites. Although commercial yeasts dominated the microflora at two sites, it appears that fears of commercial yeasts ultimately dominating the natural microflora seem to be exaggerated.
- ItemGlycerol in South African table wines : an assessment of its relationship to wine quality(South African Society for Enology and Viticulture, 2002) Nieuwoudt, Helene; Prior, B. A.; Pretorius, I. S.; Bauer, FlorianGlycerol is an important by-product of glycolysis and is quantitatively one of the major components of wine. While the physicochemical and sensory characteristics of pure glycerol are well established, the impact of varying levels of glycerol on general wine quality remains a topic of debate. Previous reports have relied on limited numbers of either commercial or experimental wines to assess the role of glycerol, leading to contradictory conclusions. Here we report on a large-scale assessment of the relationship between glycerol concentration and wine quality, based on the analysis of a significant number of commercial South African table wines of adjudged quality. The mean glycerol concentrations of 237 dry red (10.49 g/L), 158 dry white (6.82 g/L), 22 off-dry white (6.55 g/L), 16 special late harvest (8.26 g/L) and 14 noble late harvest wines (15.55 g/L) were found to be associated with considerable variation within each respective style. The final glycerol concentrations were significantly associated with the wine style (P<0.05). Shiraz wines had a mean glycerol concentration (10.22 g/L) which was significantly lower than that of Cabernet Sauvignon (10.81 g/L), Pinotage (10.46 g/L) and Merlot (10.62 g/L) wines (P<0.05). In both the dry white and off-dry white styles, the mean glycerol concentrations of Sauvignon blanc wines (6.31and5.42 g/L, respectively) were significantly lower (P<0.05) than those of the Chardonnay wines (7.08 and 7.03 g/L, respectively) and the Chenin blanc wines (6.81 and 6.85 g/L, respectively). No significant association between the final glycerol concentrations in commercial wines and the vintage, geographic origin or yeast strain used in inoculated fermentations could be established (P>0.05). The mean glycerol concentrations for South African dry red wines were significantly higher than those of dry white and off-dry white wines. Wine quality could not be significantly associated with glycerol concentrations in the dry red wines (P>0.05). For the dry white, off-dry white and late harvest wines this association was significant (P<0.05), although the exact nature of the association was somewhat different for the respective styles. Despite this positive statistical association, the observed differences between the mean glycerol concentrations of dry white and off-dry white wines of different quality ratings were too small to be of major practical value. The relationship between glycerol concentration and wine quality is reassessed on the basis of results obtained in this study as well as on recent reports in the literature.
- ItemIdentification of wine yeast strains with FT-NIRS and effect of spectral variation due to sample preparation and repeated analyses(2007) Muller, C. A.; Manley, M.; Lambrechts, M.; Pretorius, I. S.; Nieuwoudt, Helene
- ItemThe impact of yeast genetics and recombinant DNA technology on the wine industry - a review(South African Society for Enology and Viticulture, 1991) Pretorius, I. S.; Van der Westhuizen, T. J.Despite our limited knowledge of the genetic make-up of commercial wine yeasts and the fact thatthe advantages of genetic manipulation of wine yeasts have not yet been demonstrated in practice, the wine industry has to realise that "the name of the game" is recombinant DNA and that the pace of progress is fast. The technology is so powerful that it now enables manipulation of the genome in ways hard to imagine only a decade ago. In this review we highlight the importance of the wine yeast to the wine industry and the necessity for well-planned breeding programmes. First, we summarise reliable taxonomic methods that are useful as diagnostic techniques in such breeding strategies. Second, we emphasise the complexity of the genetic features of commercial wine-yeast strains. Third, we review the genetic techniques available and point out the potential of these techniques (individually and in combination) in strain-development programmes. Finally, we attempt to stimulate interest in the genetic engineering of wine yeasts by discussing a few potential targets of strain development. The impact of yeast genetics and recombinant DNA technology on the wine industry promises to be impressive.
- ItemLate fermentation expression of FLO1 in Saccharomyces cerevisae.(AMER SOC BREWING CHEMISTS INC, 3340 PILOT KNOB RD, ST PAUL, USA, MN,55121-2097, 2001) Verstrepen, K. J.; Bauer, Florian; Winderickx, J.; Derdelinckx, G.; Pretorius, I. S.; Thevelein, J. M.; Delvaux, F. R.