Browsing by Author "Malherbe, S."

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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.
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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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    Effect of magnesium on myocardial ischaemia and reperfusion injury
    (Health & Medical Publishing Group, 1999) Malherbe, S.; Conradie, S.; Coetzee, A.
    This study examined the effect of intravenous magnesium on the reperfusion injury of the porcine myocardium. Animals received general anaesthesia and the left anterior descending coronary artery was occluded for 15 minutes. Thereafter, reperfusion was allowed for 60 minutes. Regional ventricular function was measured with microsonometers. Animals were randomly assigned to a control (N = 6) or a magnesium group (N = 6). The latter received 30 mg/kg magnesium immediately before the release of the occlusion on the left anterior descending (LAD) artery. Results indicate that magnesium administration is associated with fewer ventricular arrhythmias and a rapid recovery (within 5 minutes) of myocardium systolic function once reperfusion was initiated. In the control group myocardial stunning was prolonged and more reperfusion arrhythmias occurred. However, in the group that received magnesium there was more diastolic dysfunction during reperfusion.
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    Industry-wide investigation into the occurrence and causes of problem fermentations.
    (Wynboer, 2006) Malherbe, S.; Bauer, Florian; Du Toit, M.
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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
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    Understanding problem fermentations – a review
    (South African Society for Enology and Viticulture, 2007) Malherbe, S.; Bauer, Florian; Du Toit, M.
    Despite advances in winemaking technology and improvements in fermentation control, problem alcoholic and malolactic fermentations remain a major oenological concern worldwide. This is due to possible depreciation of product quality and its consequent negative economic impact. Various factors have been identified and studied overv the years, yet the occurrence of fermentation problems persists. The synergistic effect of the various factors amongst each other provides additional challenges for the study of such fermentations. This literature review summarises the most frequently studied causes of problematic alcoholic and malolactic fermentations and in addition provides a summary of established and some potential new analytical technologies to monitor and investigate the phenomenon of stuck and sluggish fermentations.
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    Validation of two Napping techniques as rapid sensory screening tools for high alcohol products.
    (ELSEVIER SCI LTD, THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD, ENGLAND,OXON, OX5 1GB, 2013) Louw, L.; Malherbe, S.; Naes, T.; Lambrechts, M. G.; Van Rensburg, P.; Nieuwoudt, Helene