Browsing by Author "Tredoux, A. G. J."

Now showing 1 - 12 of 12
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    Analytical techniques for wine analysis : an African perspective; a review
    (2012-02-22) De Villiers, A.; Alberts, P.; Tredoux, A. G. J.; Nieuwoudt, Helene
    Analytical chemistry is playing an ever-increasingly important role in the global wine industry. Chemical analysis of wine is essential in ensuring product safety and conformity to regulatory laws governing the international market, as well as understanding the fundamental aspects of grape and wine production to improve manufacturing processes. Within this field, advanced instrumental analysis methods have been exploited more extensively in recent years. Important advances in instrumental analytical techniques have also found application in the wine industry. This review aims to highlight the most important developments in the field of instrumental wine and grape analysis in the African context. The focus of this overview is specifically on the application of advanced instrumental techniques, including spectroscopic and chromatographic methods. Recent developments in wine and grape analysis and their application in the African context are highlighted, and future trends are discussed in terms of their potential contribution to the industry. © 2011 Elsevier B.V. All rights reserved.
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    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.
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    Fermentation-derived aroma compounds in varietal young wines from South Africa
    (SASEV, 2010-09) Louw, L.; Tredoux, A. G. J.; Van Rensburg, P.; Kidd, M.; Naes, T.; Nieuwoudt, Helene
    The volatile composition of 925 single cultivar young Sauvignon blanc, Chardonnay, Pinotage, Merlot, Shiraz and Cabernet Sauvignon wines of vintages 2005 to 2007, was determined using gas chromatography-flame ionisation detection. Compositional data were compared to published data on young wines from South Africa and other countries. South African young wines analysed in this study had a largely similar volatile composition to that reported in the literature. Significant between-vintage and between-cultivar differences were observed in the volatile composition of the wines investigated in this study. The concentration ranges of four compounds in red wines, hexanol, propanol, diethyl succinate and ethyl lactate, and four compounds in white wines, 2-phenylethanol, hexanoic acid, isoamyl acetate and propanol, were not influenced by vintage effects. This finding was interpreted as the first indication that typical concentration ranges for some aroma compounds can be established for South African young cultivar wines. A trend was observed in the white wines that the alcohols and their respective acetate esters, as well as fatty acids and their ethyl esters, were responsible for the vintage-related effects. Differences in volatile composition between Chardonnay and Sauvignon blanc wines could also largely be explained on the same basis. Classification models were established to discriminate between individual red wine cultivars and between the two white wine cultivars and correct classification rates of respectively, 79 % and 85 % were achieved.
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    Quantification of glutathione, catechin and caffeic acid in grape juice and wine by a novel ultra-performance liquid chromatography method
    (2011-05) Fracassetti, D.; Lawrence, N.; Tredoux, A. G. J.; Tirelli, A.; Nieuwoudt, Helene; Du Toit, W. J.
    This research aimed at the development and validation of an ultra-performance liquid chromatography (UPLC) method for the quantification of glutathione (GSH) in grape juice and in white wine after derivatisation with para-benzoquinone. The phenolic compounds catechin and caffeic acid that occur in white wine and have antioxidant effects, are also quantified in the same analysis. Catechin is the basic monomeric unit of grape and wine tannins and caffeic acid, when esterified with tartaric acid, plays a relevant role in Grape Reaction Product (GRP) formation. The analytical method proposed showed good linearity, repeatability and intermediate repeatability, as well as high recovery (>85%). It was applied for the quantification of GSH, catechin and caffeic acid in South African juices (12) and white wines (43). This novel method will have a large impact on the time and costs of the analyses for the wine industry through enabling rapid routine quantification of GSH, catechin and caffeic acid. © 2011 Elsevier Ltd. All rights reserved.
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    Quantitative survey of 3-alkyl-2-methoxypyrazines and first confirmation of 3-ethyl-2-methoxypyrazine in South African Sauvignon blanc wines
    (South African Society for Enology and Viticulture, 2013) Alberts, P.; Kidd, M.; Stander, M. A.; Nieuwoudt, Helene; Tredoux, A. G. J.; De Villiers, A. J.
    3-Alkyl-2-methoxypyrazines are important aroma components in Sauvignon blanc wine, contributing to the typical vegetative character associated with the cultivar. The analysis of methoxypyrazines is highly challenging and, as a result, limited quantitative data are available for South African Sauvignon blanc wines. In this study, liquid chromatography-tandem mass spectrometry was applied for the sensitive quantification of the three principal methoxypyrazines in 881 South African Sauvignon blanc wines. The total wine methoxypyrazine concentration exceeded the combined recognition threshold for the vegetative aroma in more than 60% of the samples, demonstrating the involvement of these compounds in the typical aroma of the cultivar. The analytical method was adapted to allow the accurate quantitation and spectral confirmation of 3-ethyl-2-methoxypyrazine in Sauvignon blanc wines for the first time. Concentrations ranged between 1.1 and 4.9 ng/L. Statistically significant relationships between wine methoxypyrazine concentrations and parameters related to the maturity of the grapes and to the climate, as well as geographical origin and vintage, were found.
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    Stir bar sorptive extraction for the analysis of beverages and foodstuffs
    (Stellenbosch : University of Stellenbosch, 2008-03) Tredoux, A. G. J.; Sandra, P. J. F.; Crouch, A. M.; University of Stellenbosch. Faculty of Science. Dept. of Chemistry and Polymer Science.
    The main goal of this study was the development of new technologies based on modern analytical techniques for analysis of volatiles in wines. Due to the exponential growth of the wine industry and consumer demands for an enjoyable, safe-to-consume, and high quality product, the need for arose for methodologies aiding the understanding of wine better arose. Chemical analysis is a valuable way of studying the composition of wine in depth. Very sophisticated instrumentation is available nowadays but almost always the sample needs to be cleaned up or concentrated before such analysis. This study investigates the use of stir bar sorptive extraction (SBSE) as such a technique. It is shown that SBSE combined with gas chromatography-mass spectrometry (GC-MS) is extremely suited for a wide number of analyses and during the course of the study the technique was applied for troublesome analytical challenges in various beverages and foodstuffs. The study focuses on the development of a screening technique for volatiles in wine using SBSE and the application of the data to various chemometrical techniques for classification purposes. A second part of the study shows the applicability of SBSE for extraction of pesticides, contaminants and preservatives from wine, water, lemon flavoured beverages and yoghurt. The method is also elaborated upon by development of faster analysis methods for wine and beer and the investigation of using SBSE for headspace sampling of wine. In all the applications, SBSE technology was shown to be sensitive, repeatable, robust and very simple to use.
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    The relationships between consumer liking, sensory and chemical attributes of Vitis venifera L. cv. Pinotage wines elaborated with different Oenococcus oeni starter cultures
    (JOHN WILEY & SONS LTD, THE ATRIUM, SOUTHERN GATE, CHICHESTER, ENGLAND, WSUSSEX, PO19 8SQ, 2013) Malherbe, S.; Menichelli, E.; Du Toit, M.; Tredoux, A. G. J.; Muller, M.; Naes, T.; Nieuwoudt, Helene