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Browsing by Author "Du Toit, M."

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Analysis of volatile profiles of fermenting grape must by headspace solid-phase dynamic extraction coupled with gas chromatography-mass spectrometry (HS-SPDE GC-MS): Novel application to investigate problem fermentations
(2009) Malherbe, S.; Watts, V.; Nieuwoudt, Helene; Bauer, Florian; Du Toit, M.
The occurrence of stuck and sluggish wine fermentations is a persisting problem in the wine industry worldwide. This study illustrates the suitability of headspace solid-phase dynamic extraction coupled with gas chromatography-mass spectrometry (HS-SPDE GC-MS) for wine analysis and the subsequent application to discriminate between control and problem fermentations using partial least-squares discriminant analysis (PLS-DA) models. The specific analytical technique is relatively new and has not yet to the authors' knowledge been evaluated for the analysis of wine within this context of problem fermentations. HS-SPDE GC-MS was used to determine 68 volatile compounds (higher alcohols, fatty acids, esters, and carbonyl compounds) in 94 monovarietal fermenting must samples consisting of 56 red and 38 white cultivars. PLS-DA models showed the potential to discriminate between control and problem fermentations using corrected peak area headspace data for the 68 analytes. This possibility to discriminate between problem and control fermentations with only the headspace data could possibly be applied for the prediction of problem fermentations in future studies and to better understand the chemical causes of problem fermentations. ©2009 American Chemical Society.
Biogenic 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.
Bioprocess monitoring of alcoholic wine fermentation using on-line NIR infrared spectroscopy.
(2011) Nieuwoudt, Helene; Kruger, van Eck M.; Du Toit, M.; Silva Ferreira, A. C.; Tredoux, A G J.
Characterisation 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.
Comparative metabolic profiling to investigate the contribution of O. oeni MLF starter cultures to red wine composition
(2011) Malherbe, S.; Tredoux, A. G. J.; Nieuwoudt, Helene; Du Toit, M.
In this research work we investigated changes in volatile aroma composition associated with four commercial Oenococcus oeni malolactic fermentation (MLF) starter cultures in South African Shiraz and Pinotage red wines. A control wine in which MLF was suppressed was included. The MLF progress was monitored by use of infrared spectroscopy. Gas chromatographic analysis and capillary electrophoresis were used to evaluate the volatile aroma composition and organic acid profiles, respectively. Significant strain-specific variations were observed in the degradation of citric acid and production of lactic acid during MLF. Subsequently, compounds directly and indirectly resulting from citric acid metabolism, namely diacetyl, acetic acid, acetoin, and ethyl lactate, were also affected depending on the bacterial strain used for MLF. Bacterial metabolic activity increased concentrations of the higher alcohols, fatty acids, and total esters, with a larger increase in ethyl esters than in acetate esters. Ethyl lactate, diethyl succinate, ethyl octanoate, ethyl 2-methylpropanoate, and ethyl propionate concentrations were increased by MLF. In contrast, levels of hexyl acetate, isoamyl acetate, 2-phenylethyl acetate, and ethyl acetate were reduced or remained unchanged, depending on the strain and cultivar evaluated. Formation of ethyl butyrate, ethyl propionate, ethyl 2methylbutryate, and ethyl isovalerate was related to specific bacterial strains used, indicating possible differences in esterase activity. A strain-specific tendency to reduce total aldehyde concentrations was found at the completion of MLF, although further investigation is needed in this regard. This study provided insight into metabolism in O. oeni starter cultures during MLF in red wine. © 2011 Society for Industrial Microbiology and Biotechnology.
The effect of micro-oxygenation on the phenolic composition, quality and aerobic wine-spoilage microorganisms of different South African red wines
(South African Society for Enology and Viticulture, 2006) Du Toit, W. J.; Lisjak, K.; Marais, J.; Du Toit, M.
The effect of micro-oxygenation treatments on the composition of different South African red wines was evaluated. In some wines, micro-oxygenation led to an increase in colour density, with a corresponding change in colour, due to the formation of polymeric pigments. This increase also led to the red colour becoming more resistant to the bleaching effect of SO2. Micro-oxygenation also seemed to be more effective in increasing the colour densities of younger red wines than the older ones, although total red pigments were found to be highest in an older red wine that had received micro-oxygenation. Differences in the gelatine index were also observed over time. The micro-oxygenated and barrel-matured wines also had lower concentrations of catechin and the procyanidin B1, and showed a corresponding increase in polymeric pigment and polymeric phenols. Micro-oxygenation led to higher acetic acid bacteria counts, although no increase in volatile acidity was observed in these wines. A tasting panel preferred younger red wines that had undergone micro-oxygenation. In an older red wine prolonged micro-oxygenation led to the wine becoming over-aged, with an increase in the barnyard/medicinal character, which corresponded with an increase in Brettanomyces counts. Micro-oxygenation can be used to increase the quality of young red wines, but further research is needed in this area.
Functional wine-omics.
(2008) Bauer, Florian; Naes, T.; Esbensen, K. H.; Young, P. R.; Du Toit, M.; Vivier, M. A.
Genetic screening of wine-related enzymes in Lactobacillus species isolated from South African wines
(2010) Mtshali, P. S.; Divol, Benoit; Van Rensburg, P.; Du Toit, M.
Aims: The objective of this study was to investigate the presence of genes coding for enzymes of oenological relevance in wine Lactobacillus strains isolated from South African grape and wine samples during the 2001 and 2002 harvest seasons. Methods and Results: A total of 120 wine lactobacilli isolates belonging to Lactobacillus plantarum, Lactobacillus hilgardii, Lactobacillus brevis, Lactobacillus pentosus, Lactobacillus paracasei, Lactobacillus sakei and Lactobacillus paraplantarum were genetically screened for enzyme-encoding genes using PCR with primers specific for β-glucosidase, protease, esterase, citrate lyase and phenolic acid decarboxylase. The results of PCR screening showed that the Lactobacillus strains possessed different combinations of enzymes and that some strains did not possess any of the enzymes tested. Confirmation analysis with gene sequencing also showed high similarity of genes with those available in GenBank database. Conclusion: In this study, we have demonstrated the existence of genes coding for wine-related enzymes in wine lactobacilli that could potentially hydrolyse wine precursors to positively influence wine aroma. Significance and Impact of the Study: An expansion of knowledge on the genetic diversity of wine-associated lactic acid bacteria will enable the selection of novel malolactic fermentation starter cultures with desired oenological traits for the improvement of the organoleptic quality of the wine, and hence wine aroma. © 2009 The Authors.
Guideline for the treatment of myelodysplastic syndromes (MDS) in South Africa
(Health and Medical Publishing Group (HMPG), 2011-12) Louw, V. J.; Bassa, F.; Chan, S. W.; Dreosti, L.; Du Toit, M.; Ferreira, M.; Gartrell, K.; Gunther, K.; Jogessar, V.; Littleton, N.; Mahlangu, J.; McDonald, A.; Patel, M.; Pool, R.; Ruff, P.; Schmidt, A.; Sissolak, G.; Swart, A.; Verburgh, E.; Webb, M. J.
Introduction. Myelodysplastic syndromes (MDS) encompass a heterogeneous group of clonal haematopoietic disorders characterised by chronic and progressive cytopenias resulting from ineffective haematopoiesis. Treatment is complicated by differences in disease mechanisms in different subgroups, variable clinical phenotypes and risk of progression to acute myeloid leukaemia. Rationale. Changes in disease classification, prognostic scoring systems, the availability of novel treatment options and the absence of South African guidelines for the diagnosis and management of these complex disorders underpinned the need for the development of these recommendations. Methods. These recommendations are based on the opinion of a number of experts in the field from the laboratory as well as clinical settings and came from both the private and institutional academic environments. The most recent literature as well as available guidelines from other countries were discussed and debated at a number of different meetings held over a 2-year period. Results. A comprehensive set of recommendations was developed focusing on risk stratification, supportive management and specific treatment. Novel agents and their indications are discussed and recommendations are made based on best available evidence and taking into account the availability of treatments in South Africa. Conclusion. Correct diagnosis, risk stratification and appropriate therapeutic choices are the cornerstones of success in the management of patients with MDS.
Identification and characterization of Lactobacillus florum strains isolated from South African grape and wine samples
(ELSEVIER SCIENCE BV, PO BOX 211, AMSTERDAM, NETHERLANDS, 1000 AE, 2012) Mtshali, P. S; Divol, Benoit; Du Toit, M.
Identification and characterization of Lactobacillus florum strains isolated from South African grape and wine samples
(2012) Mtshali, P. S.; Divol, Benoit; Du Toit, M.
A total of 213 strains of lactic acid bacteria were examined in this study. Among these, 30 strains previously isolated from South African grape and wine samples remained unidentified. The identification of these isolates was performed by BLAST and phylogenetic analyses of 16S rDNA gene sequences, which indicated that the isolates belonged to Lactobacillus florum. In this work, we also designed a discriminative species-specific primer FLOR targeting the 16S rDNA gene of Lb. florum. The validity and specificity of this primer was confirmed. Of particular interest in this study was to further evaluate the identified strains for the presence of genes encoding enzymes of oenological relevance. Reference strains included three flower-associated Lb. florum (F9-1 T, F9-2 and F17) and two Lactobacillus lindneri (AWRI B530 and DSM 20691) strains. Lb. lindneri strains were incorporated as being the closest relatives of Lb. florum. PCR detection results revealed that all Lb. florum strains and Lb. lindneri AWRI B530 (grape isolate) possessed the majority of the tested genes relative to DSM 20691 (beer isolate); these enzyme-encoding genes included malolactic enzyme, peptidases (PepC, PepI, PepN), citrate lyase (α- and β-subunits), phenolic acid decarboxylase and arginine deiminase pathway enzymes (arginine deiminase and ornithine transcarbamylase). Sequence verification of PCR-generated fragments was performed by sequencing. The sequence data were used to construct the phylogenetic trees, which indicated that our Lb. florum isolates cluster with other Lb. florum strains of flower origin but rather distinct from other LAB species, with Lb. lindneri being the next closest species. © 2011 Elsevier B.V.
Industry-wide investigation into the occurrence and causes of problem fermentations.
(Wynboer, 2006) Malherbe, S.; Bauer, Florian; Du Toit, M.
Malolactic fermentation : the ABC's of MLF
(SASEV, 2010-09) Lerm, E.; Engelbrecht, L.; Du Toit, M.
There are two main fermentations associated with the winemaking process. Alcoholic fermentation is conducted by the yeast culture and malolactic fermentation takes place as a result of the metabolic activity of lactic acid bacteria, specifically from the genera Oenococcus, Lactobacillus, Pediococcus and Leuconostoc. Malolactic fermentation is dened as the conversion of malic acid to lactic acid and CO2 and besides deacidification also contributes to microbial stability and modification of the aroma prole. This paper aims to provide a comprehensive review discussing all the main aspects and factors related to malolactic fermentation, including practical considerations for monitoring and ensuring a successful fermentation.
Microbial spoilage and preservation of wine : using weapons for nature's own arsenal
(South African Journal of Enology and Viticulture, 2000) Du Toit, M.; Pretorius, I. S.
The winemaking process includes multiple stages at which microbial spoilage can occur, altering the quality and hygienic status of the wine and rendering it unacceptable. The major spoilage organisms include species and strains of the yeast genera Brettanomyces, Candida, Hanseniaspora, Pichia, Zygosaccharomyces etc., the lactic acid bacterial genera Lactobacillus, Leuconostoc, Pediococcus, etc. and the acetic acid bacterial genera Acetobacter and Gluconobacter. The faults caused include bitterness and off.flavours (mousiness, ester taint, phenolic, vinegary, buttery, geranium tone), and cosmetic problems such as turbidity, viscosity, sediment and film formation. These spoilage organisms can also affect the wholesomeness of wine by producing biogenic amines and precursors of ethyl carbamate. The judicious use of chemical preservatives such as sulphur dioxide (S02) during the winemaking process decreases the risk of microbial spoilage, but strains vary considerably in their S02 sensitivity. There is, moreover, mounting consumer bias against chemical preservatives, and this review focuses on the possible use of biopreservatives in complying with the consumers' demand for "clean and green" products.
Non-Saccharomyces yeast and lactic acid bacteria in Co-inoculated fermentations with two Saccharomyces cerevisiae yeast strains : a strategy to improve the phenolic content of Syrah wine
(MDPI, 2019) Minnaar, P. P.; Du Plessis, H. W.; Jolly, N. P.; Van Der Rijst, M.; Du Toit, M.
Syrah must was co-inoculated with mixed cultures of Saccharomyces + O. oeni/Lb. plantarum and Saccharomyces + non-Saccharomyces + O. oeni/Lb. plantarum to evaluate the effect on phenolics and sensory attributes. Reference wines were produced by S. cerevisiae. Malvidin-3-O-glucoside, flavan-3-ols, flavonols and phenolic acids were quantified using a RP-HPLC technique. Physicochemical characteristics and sensory attributes were measured. Total acidity and alcohol in mixed co-inoculations were different from reference wines. The concentration of l-malic acid was 7-times less in mixed co-inoculations. Mixed co-inoculations had ca. 1.3-times more malvidin-3-O-glucoside and phenolic acids than reference wines. Flavan-3-ols and flavonols were not different between mixed co-inoculations and reference wines. Acidity and astringency were least in mixed co-inoculations. Mouthfeel and bitterness least in S. cerevisiae wines. Tasters preferred mixed co-inoculated wines. Mixed co-inoculation is a strategy to contemplate for Syrah vinification but the modalities of inoculation need further investigation. Success depends on a suitable combination of yeast/bacteria and consideration of strain variation.
Optimisation of the quantification of total soluble solids, ph and titratable acidity in South African grape must using Fourier transform mid-infrared spectroscopy
(South African Society for Enology and Viticulture, 2007) Swanepoel, M.; Du Toit, M.; Nieuwoudt, Helene
Calibration models for Fourier transform mid-infrared (FT-MIR) spectroscopy were developed for the simultaneous quantification of total soluble solids (TSS, measured as °Brix), pH and titratable acidity (TA, expressed as g/L tartaric acid) in South African (SA) grape must. An exploratory data analysis of the FT-MIR spectra of 1170 grape must samples (647 for °Brix, 252 for pH and 271 for TA) was done by principal component analysis, and partial least squares regression was used for the computation of the regression models. The prediction errors for TSS (0.34°Brix), pH (0.04 units) and TA (0.51 g/L) provided analytical data of satisfactory accuracy. The evaluation of readyto-use global calibrations to quantify these three parameters in SA samples presented standard error of prediction (SEP) values of 0.46°Brix, 0.10 pH units and 3.13 g/L for TA. After slope and intercept adjustments of the original global calibration algorithms, the SEP values were reduced to 0.38 °Brix, 0.05 pH units and 0.49 g/L for TA. These results show the necessity for optimisation of the global FT-MIR WineScan calibrations to provide a better fit to samples of South African origin. The results demonstrate that FT-MIR spectroscopy is a useful technique for the rapid quantification of major grape must parameters and for quality control purposes in an industrial cellar.
Oxygen in must and wine : a review
(South African Society for Enology and Viticulture, 2006) Du Toit, W. J.; Marais, J.; Pretorius, I. S.; Du Toit, M.
Oxygen can play an important role during the winemaking process. It can influence the composition and quality of the must and wine. Phenolic compounds are the main substrates for oxidation in must and wine. Oxygen addition leads to colour changes and the polymerisation of phenolic molecules in wine. Oxygen can, however, also influence the flavour and microbial composition of wine drastically, with certain off-flavours being formed and spoilage micro-organisms able to grow at too high oxygen additions to wine. A state-of-the-art, up-to-date review on the effects of oxygen in must and wine has, however, not been published recently. This review focuses on the effects of oxygen in must, during alcoholic fermentation, extended lees contact and during ageing of white and red wines. The effects it has on acetic acid bacteria and Brettanomyces are also discussed, as well as micro-oxygenation, a relative new technique used in wine production.
PCR detection of enzyme-encoding genes in Leuconostoc mesenteroides strains of wine origin
(2012) Mtshali, P. S.; Divol, Benoit; Du Toit, M.
Fifteen isolates of lactic acid bacteria originating from South African grape and wine samples were identified as Leuconostoc mesenteroides subsp. mesenteroides through the taxonomic analysis of their 16S rDNA gene sequences. These isolates were further tested for the presence of genes coding for enzymes of oenological relevance using PCR detection technique. A type strain of Leuc. mesenteroides (NCDO 529 T) was also incorporated for comparative analysis. From the PCR detection results, the estA, prtP, alsD, alsS, metK, metC and metB genes were present in all the strains tested. The bgl and gshR genes encoding β-glucosidase and glutathione reductase, respectively, were not detected in some strains. On the other hand, none of the tested strains possessed the genes encoding phenolic acid decarboxylase (padA), citrate permease (citP), citrate lyase (citD, citE and citF) and arginine deiminase pathway enzymes (arcA, arcB and arcC). The verification of PCR-generated fragments was performed by sequencing. GenBank database was used to search for homologous DNA sequences. Neighbour-joining trees based on nucleotide sequences of alsS, estA, metK and mleA genes were also constructed in order to study the phylogenetic relationship between Leuc. mesenteroides strains and closely related species. The phylogenetic analyses revealed that there are genetic heterogeneities between strains of Leuc. mesenteroides species. In conclusion, this study has improved our knowledge on the genetics of oenological strains of Leuc. mesenteroides and their genetic potential to contribute to certain wine aroma compounds. © 2011 Springer Science+Business Media B.V.
Saccharomyces cerevisiae, non-saccharomyces yeasts and lactic acid bacteria in sequential fermentations : effect on phenolics and sensory attributes of South African syrah wines
(South African Society for Enology and Viticulture, 2017) Minnaar, P. P.; Du Plessis, H. W.; Paulsen, V.; Ntushelo, N.; Jolly, N. P.; Du Toit, M.
Wine consumers predominantly use visual, sensory and textual descriptors as quality/preference indicators to describe olfactory sensations. In this study, different wines were analysed to generate relevant chemical and sensory characterisation data and attributes. Sequential inoculation of Syrah grape must was performed with a combination of Saccharomyces yeast, non-Saccharomyces yeasts and lactic acid bacteria for the possible improvement of Syrah wine quality. Selected anthocyanins, flavan-3-ols, flavonols and phenolic acids were quantified in Syrah wines using the reversed-phase high-performance liquid chromatography photodiode array detection (RP-HPLC-DAD) technique. Sensory (descriptive evaluation) and physicochemical/oenological parameters (Winescan® and OenoFoss™) results were compared to phenolic compound concentrations. Phenolic compound concentrations increased in Syrah wines made with a combination of a Saccharomyces reference yeast, non-Saccharomyces yeasts and lactic acid bacteria. Syrah wines made with a combination of Metschnikowia pulcherrima + Saccharomyces cerevisiae + Oenococcus oeni, and M. pulcherrima + S. cerevisiae + Lactobacillus plantarum, had higher flavonol concentrations compared to wines made without lactic acid bacteria. Syrah wines made with a combination of Saccharomyces cerevisiae (Sc) + Oenococcus oeni (LAB1) were highest in phenolic acid concentrations. Syrah wines made with a combination of M. pulcherrima + S. cerevisiae + L. plantarum had higher total anthocyanins than wines made without lactic acid bacteria. Syrah wine sensory attributes, viz. mouthfeel and astringency, correlated with a combination of lactic acid bacteria and yeast treatments. Syrah wines made with a combination of yeast and lactic acid bacteria (LAB) scored highest in overall quality. Indications are that the S. cerevisiae reference yeast retained more phenolic compounds during fermentation when compared to wines made with a combination of non-Saccharomyces yeasts and LAB. The improved red colour of Syrah wines may be achieved by sequential inoculation with non-Saccharomyces yeast and LAB. This could be beneficial where winemakers use grape cultivars with low anthocyanin levels in the grape skin to produce wines of improved quality.
Selection and characterisation of oenococcus oeni and lactobacillus plantarum South African wine isolates for use as malolactic fermentation starter cultures
(South African Journal for Enology and Viticulture, 2011) Lerm, E.; Engelbrecht, L.; Du Toit, M.
This study focused on characterising 23 Oenococcus oeni and 19 Lactobacillus plantarum strains isolated from the South African wine environment for the development of potential commercial malolactic fermentation (MLF) starter cultures. These strains were characterised with regards to oenological important characteristics, including the genetic screening for enzyme-encoding genes (enzymes that are involved/implicated in wine aroma modification, as well as enzymes pertaining to the wholesomeness of the final wine product), their fermentation capabilities, the ability to maintain viability during MLF, as well as the volatile acidity production. A total of three O. oeni and three L. plantarum strains were selected at the completion of this study. These six strains showed the most potential during the characterisation stages of the study and were able to successfully complete MLF in Pinotage wine. It was also found that L. plantarum strains displayed a more diverse enzyme profile than O. oeni strains, particularly with regards to the presence of the aroma-modifying enzymes β-glucosidase and phenolic acid decarboxylase (PAD), which implies the future use of this species in the modification of the wine aroma profile and use as commercial starter culture.

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