Browsing by Author "Tredoux, A. G. J."
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- ItemAnalytical techniques for wine analysis : an African perspective; a review(2012-02-22) De Villiers, A.; Alberts, P.; Tredoux, A. G. J.; Nieuwoudt, HeleneAnalytical 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.
- ItemComparative 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.
- ItemInvestigation of the volatile composition of pinotage wines fermented with different malolactic starter cultures using comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC×GC-TOF-MS)(2011) Vestner, J.; Malherbe, S.; Du Toit M.; Nieuwoudt, Helene; Mostafa, A.; Goreck,i T.; Tredoux, A. G. J.; De Villiers, A.
- Itemn Ondersoek na die vlugtige samestelling van geselekteerde Suid-Afrikaanse jong wyne met behulp van GC-FID tegnologie (Deel 1): Inleiding tot vlugtige verbindings in wyn.(Wynboer, 2010) Louw, L.; Tredoux, A. G. J.; Nieuwoudt, Helene; Van Rensburg, P.
- Itemn Ondersoek na die vlugtige samestelling van geselekteerde Suid-Afrikaanse jong wyne met behulp van GC-FID tegnologie (Deel 2): Die veranderinge in die vlugtige samestelling van jong wyne oor drie oesjare.(Wynboer, 2010) Louw, L.; Tredoux, A. G. J.; Nieuwoudt, Helene; Van Rensburg, P.
- Itemn Ondersoek na die vlugtige samestelling van geselekteerde Suid-Afrikaanse jong wyne met behulp van GC-FID tegnologie (Deel 3): Die verskille in die vlugtige samestelling van ses belangrike kultivarwyne.(Wynboer, 2010) Louw, L.; Tredoux, A. G. J.; Nieuwoudt, Helene; Van Rensburg, P.
- Itemn Ondersoek na die vlugtige samestelling van geselekteerde Suid-Afrikaanse jong wyne met behulp van GC-FID tegnologie (Deel 4): Die klassifisering van wynkultivars op grond van hul vlugtige samestelling.(Wynboer, 2010) Louw, L.; Tredoux, A. G. J.; Nieuwoudt, Helene; Van Rensburg, P.
- ItemQuantification 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.