SUNScholar - Browsing by Author "Marais, J."

Browsing by Author "Marais, J."

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Carotenoid levels in maturing grapes as affected by climatic regions, sunlight and shade
(South African Society for Enology and Viticulture, 1991) Marais, J.; Van Wyk, C. J.; Rapp, A.
The effect of climatic region, degree of ripeness, sunlight and shade on carotenoid concentrations in Weisser Riesling and Chenin blanc grapes was investigated. Lutein and beta-carotene concentrations were higher in grapes from hot regions than grapes from cooler regions. In general, decreases in carotenoid concentrations were observed with an increase in ripeness. Also, grapes exposed to sunlight generally had lower carotenoid concentrations than shaded grapes. Both lutein and beta-carotene concentrations varied little between Weisser Riesling and Chenin blanc grapes at comparable ripening stages.
Characterisation of pinotage wine during maturation on different oak products
(SASEV, 2008-01) De Beer, D.; Joubert, E.; Marais, J.; Du Toit, W.; Fourie, B.; Manley, M.
The effect of oak contact on the phenolic composition, total antioxidant capacity (TAC) and colour of Pinotage wines was investigated during maturation. Oak maturation included traditional treatments, such as new, second-fill and third-fill barrels, as well as alternative treatments (oak chips, staves, extract and dust) applied in old barrels over a period of 28 weeks. Oak maturation using traditional and alternative treatments improved the objective colour of Pinotage wine by decreasing the L* value. Losses in TAC caused by decreased concentrations of monomeric phenolic compounds (most anthocyanins, flavan-3-ols, flavonols and hydroxycinnamic acids) during oak maturation were negated by increased concentrations of gallic acid and the formation of new oligomeric and polymeric pigments. Wine maturation in stainless steel containers also resulted in a decrease in anthocyanin content. The decrease in phenolic acid content for wines matured in stainless steel was less pronounced, while their flavan-3-ol content remained stable. The new-barrel treatment had the most pronounced effect on all parameters. Oak maturation can be used for the production of Pinotage wine when the retention of TAC is a high priority.
Climatic region and vine structure : effect on pinotage wine phenolic composition, total antioxidant capacity and colour
(South African Society for Enology and Viticulture, 2006) De Beer, D.; Joubert, E.; Marais, J.; Van Schalkwyk, D.; Manley, M.
The phenolic composition, total antioxidant capacity (TAC) and colour of Pinotage wines of the 2001, 2002 and 2003 vintages were investigated, using spectrophotometric, high-performance liquid chromatography (HPLC), free radical scavenging and objective colour analyses. Grapes were harvested from grapevines in three climatic regions ranging from cool to warm, with bush (20- and 30-cm trunk height) and trellised (30- and 60-cm trunk heights) vine treatments, on several vineyard sites in each climatic area. Climatic region had a significant effect on the content of several phenolic compounds; the concentration of anthocyanin monoglucosides, flavonols, flavan-3-ols and tartaric acid esters of hydroxycinnamic acids generally increased as the climatic region becomes cooler, while concentrations of acylated derivatives and free hydroxycinnamic acids decreased. Wines made from bush vines contained higher concentrations of flavonols, gallic acid and flavan-3-ols than those from trellised vines, but lower concentrations of some anthocyanin monoglucosides and acylated derivatives, as well as non-coloured polymers. These trends resulted in differences in TAC and objective colour parameters, although the different vintages did not show the same trends in all cases. More vintages should therefore be investigated to clarify these effects. Wines from the cool climatic regions and from bush vines were generally darker coloured, with higher TAC than those from the warm climatic regions and bush vines, respectively. High TAC, therefore, coincided with higher colour quality. Variations in TAC were partly explained by trends for individual phenolic compounds, although unknown compounds played a major role.
Effect of ascorbic acid and yeast strain on sauvignon blanc wine quality
(South African Society for Enology and Viticulture, 2001) Swart, E.; Marais, J.; Britz, T. J.
Sauvignon blanc cultivar-typical aroma is affected by different components of which 2-methoxy-3-isobutylpyrazine and 4-mercapto-4-methylpentan-2-one are probably the most important. Climatic, viticultural and oenological conditions may have a prominent effect on the levels at which these impact aroma components occur in wine. Sauvignon blanc wines were produced from grapes from two climatically different regions. Different ascorbic acid/S02 combinations and different Saccharomyces cerevisiae yeast strains were used during the production of the wines. The wines were sensorially evaluated for specific wine characteristics, namely fruity/ester aroma intensity, grassy/green pepper aroma intensity, sulphur-like aroma intensity and overall wine quality. Significant differences were observed between treatments. A commercially available preparate (ascorbic acid/meta-bisulphite) and yeast strain VL3C produced sulphur-like, low-quality wines under the conditions of this investigation. The highest quality wines were produced from pure ascorbic acid/S02 treatments and fermentation by the yeast strain VIN 13.
Effect of grape maturity and juice treatments on terpene concentrations and wine quality of Vitis vinifera L. cv. Weisser Riesling and Bukettraube
(South African Society for Enology and Viticulture, 1986) Marais, J.; Van Wyk, C. J.
The effect of grape maturity aud different juice treatments, namely free-run, skin-contact, pressing and heat treatment on individual terpene concentrations in Weisser Riesling and Bukettraube juices and wines, as well as on different wine quality parameters, was investigated. Linalool, hotrienol, alpha-terpineol, nerol, geraniol, citronellol, 3,7-dimethylocta-1,5-dien-3,7-diol and the furan and pyran Iinalool oxides were analysed gas chromatographically. Wine quality parameters, such as terpene-like character, cultivar authenticity and overall wine quality of these wines were sensorially evaluated. Increases in grape maturity and the application of juice treatments, like skin-contact and heat treatment, caused significant increases in the concentrations of the majority of terpenes analysed. These changes were, to a limited extent, reflected in the intensities and qualities of some wine characteristics. Heat treatment emerged as the single factor, causing the most prominent increases in terpene concentrations and improvement in overall wine quality.
Effect of juice turbidity and yeast lees content on brandy base wine and unmatured pot-still brandy quality
(South African Society for Enology and Viticulture, 2005) Van Jaarsveld, F. P.; Blom, M.; Hattingh, S.; Marais, J.
The aims of this project were to identify a suitable grape juice clarification technique for the attainment of the optimal brandy base wine turbidity, to determine the importance of chemical components (volatile components and long-chain fatty acids) in brandy base wine and unmatured pot-still brandy quality, and to study the effect of yeast lees content on quality. Although common industry practice is to use the grape cultivars Colombar(d) and Chenin blanc for the production of brandy base wine, the optimal conditions for Chenin blanc have been defined in this study. The juice clarification treatments applied included no settling, cold settling, whisk, large- and small-scale centrifugation and bentonite. Yeast strain 228 was compared with VIN13, large-scale (L) distillation was compared with small-scale (s) distillation, and the use of no enzyme was compared with the use of pectolytic enzyme. The data for four vintages were compiled and evaluated. Settling with or without pectolytic enzyme, bentonite, small-scale centrifugation and whisk treatments gave clearer Chenin blanc juice, higher concentrations of certain volatile components and long-chain fatty acids, and higher quality brandy base wine and unmatured pot-still brandy. No settling and large-scale centrifugation yielded the most turbid and lowest quality products. There is a definite relationship between treatments, turbidity, concentrations of esters, higher alcohols and acids, and overall brandy base wine and unmatured pot-still brandy quality. The use of yeast strain VIN13 (as opposed to strain 228), in conjunction with an increased yeast lees content of 1.5x that is normally found in brandy base wine, yielded the best quality unmatured pot-still brandy. Based on the results of this study, it is possible to recommend the best juice clarification method(s) for optimal turbidity as well as optimal levels of yeast lees addition, and to identify chemical compounds that positively relate to quality.
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.
Effect of oxygenation during maturation on phenolic composition, total antioxidant capacity, colour and sensory quality of pinotage wine
(SASEV, 2008-10) De Beer, D.; Joubert, E.; Marais, J.; Manley, M.
The effect of oxygenation on the phenolic composition, total antioxidant capacity (TAC), colour and sensory quality was investigated during the maturation of Pinotage wines. Oxygenation was carried out in discrete monthly doses at two oxygen dosages (2.5 and 5.0 mg O2/L/month) for zero, two, four and six months. Oxygenation at the lower dosage for two months had beneficial effects on the colour and sensory quality of Pinotage wine. The higher oxygen dosage (all times) and longer times (all dosages) had a substantial detrimental effect on the overall sensory quality of the wine. A decrease in the TAC of the wine was observed for all the treatment combinations, despite increased concentrations of gallic acid. During the following harvest, a modified oxygenation treatment, entailing 1.0 mg O2/L in discrete doses every two weeks for two months, was tested. It had little effect on the wine phenolic composition and was not detrimental to the TAC of the wine. The modified oxygenation protocol significantly reduced the berry/ plum intensity of the Pinotage wine without negatively affecting the overall sensory quality. Oxygen addition on a continuous basis may also be less detrimental to the TAC of the wine and provide improved sensory quality.
Effect of region on free and bound monoterpene and C13-N orisoprenoid concentrations in Weisser Riesling wines
(South African Society for Enology and Viticulture, 1992) Marais, J.; Versini, G.; Van Wyk, C. J.; Rapp, A.
Free and bound monoterpene and C 13-norisoprenoid concentrations of Weisser Riesling wines of different vintages and from different regions in South Africa, Germany and Northern Italy were compared. The concentrations of some of these compounds differed between climatic regions. For example, older Weisser Riesling wines from South Africa displayed significantly higher 1,1,6-trimethyl-1,2-dihydronaphthalene (TDN), trans-vitispirane and trans- 1,8-terpin concentrations than those from the cooler European countries. Canonical and stepwise discriminant analysis of the wine data allowed the successful classification of the wines according to origin. A comparison of meteorological data of the countries revealed that in the cooler wine regions of Germany and Northern Italy the average daily temperatures were lower, the average monthly rainfall higher and the daily sunshine hours fewer than in the warmer South African wine regions.
Effect of storage time, temperature and region on the levels of 1, l ,6-trimethyl-1,2-dihydronaphthalene and other volatiles, and on quality of weisser riesling wines
(South African Society for Enology and Viticulture, 1992) Marais, J.; Van Wyk, C. J.; Rapp, A.
A survey of the concentration levels of 1,1,6-trimethyl-1,2-dihydronaphthalene (TDN) in wines of different cultivars, vintages and regions was conducted. The TDN concentrations of South African Weisser Riesling wines were higher than those from Germany and Italy, and those of other cultivars. The effect of storage time and temperature on free and precursor TDN concentrations, on the concentrations of free trans-vitispirane, some monoterpenes, esters and higher alcohols, and on the quality of Weisser Riesling wines was investigated. Three Weisser Riesling wines from different regions were stored at 15°C and 30°C for four years and one year, respectively. These wines were analysed periodically by gas chromatography and evaluated sensorially. The concentrations of TDN, trans-vitispirane, 2,6-dimethyl-7-octen-2,6-diol and trans-1,8-terpin, and the intensity of the bottle-aged kerosene-like character increased significantly with ageing. During the same period, significant decreases occurred in the concentrations of diendiol-1, linalool, i-amyl acetate, ethyl caproate, hexyl acetate, 2-phenethyl acetate, hexanol, 2-phenyl ethanol, and in the intensity of young wine character. alpha-Terpineol showed significant increases followed by decreases under the same conditions. These changes in concentrations were more prominent at 30°C than at 15°C storage. The development of the kerosene character in Weisser Riesling wines was restricted to sensorially acceptable levels by storage at 15°C.
Effect of sunlight and shade on norisoprenoid levels in maturing weisser riesling and chenin blanc grapes and weisser riesling wines
(South African Society for Enology and Viticulture, 1992) Marais, J.; Van Wyk, C. J.; Rapp, A.
The effect of sunlight, shade and degree of ripeness on potentially volatile C13-norisoprenoid concentrations in Weisser Riesling grapes and wines and in Chenin blanc grapes, was investigated. Norisoprenoids were released from their bound forms by acid and enzymatic hydrolysis. With few exceptions, norisoprenoid concentrations were significantly higher in sun-exposed grapes than in shaded grapes. Significant increases in norisoprenoid concentrations were observed with an increase in ripeness. Microclimatic conditions during grape ripening for the production of Weisser Riesling wine with a potential to form lower concentrations of TDN during ageing are proposed.
Maceration before and during fermentation : effect on pinotage wine phenolic composition, total antioxidant capacity and objective colour parameters
(South African Society for Enology and Viticulture, 2006) De Beer, D.; Joubert, E.; Marais, J.; Manley, M.
Low-temperature maceration treatments (1, 2 and 4 days at 10 and 15°C) before fermentation and juice/skin mixing treatments (punching-down, pumping-over and rotor action every hour and every 3 hours) during fermentation were investigated in terms of their effects on Pinotage wine phenolic composition, total antioxidant capacity (TAC) and colour over three vintages (2000 to 2002). Results for pre-fermentation maceration were not consistent between vintages. Very few significant differences in the phenolic content, TAC and objective colour parameters were observed between the control wines and wines subjected to different pre-fermentation maceration treatments. Pre-fermentation maceration, especially at 15°C, resulted in wines with increased vitisin A content. Improvement of wine quality when using pre-fermentation maceration treatments at 10°C was noted previously, while no detrimental effect on the wine TAC was observed. The pumping-over treatment yielded wines with lower TAC and phenol content, as well as less favourable objective colour values, indicating that the punching-down or rotor treatment would be preferred. Although mixing at hourly intervals yielded a higher content of some phenolic compounds compared to the 3-hour interval mixing, mixing frequency did not affect the TAC of the wine. The objective colour parameters, h* and b*, were slightly lower at the higher mixing frequency in 2002 indicating a shift in the direction of a magenta hue.
Optimising perioperative care for hip and knee arthroplasty in South Africa : a Delphi consensus study
(BioMed Central, 2018-05-09) Plenge, U.; Nortje, M. B.; Marais, L. C.; Jordaan, J. D.; Parker, R.; Van der Westhuizen, N.; Van der Merwe, J. F.; Marais, J.; September, W. V.; Davies, G. L.; Pretorius, T.; Solomon, C.; Ryan, P.; Torborg, A. M.; Farina, Z.; Smit, R.; Cairns, C.; Shanahan, H.; Sombili, S.; Mazibuko, A.; Hobbs, H. R.; Porrill, O. S.; Timothy, N. E.; Siebritz, R. E.; Van der Westhuizen, C.; Troskie, A. J.; Blake, C. A.; Gray, L. A.; Munting, T. W.; Steinhaus, H. K. S.; Rowe, P.; Van der Walt, J. G.; Isaacs Noordien, R.; Theron, A.; Biccard, B. M.
Background: A structured approach to perioperative patient management based on an enhanced recovery pathway protocol facilitates early recovery and reduces morbidity in high income countries. However, in low- and middle-income countries (LMICs), the feasibility of implementing enhanced recovery pathways and its influence on patient outcomes is scarcely investigated. To inform similar practice in LMICs for total hip and knee arthroplasty, it is necessary to identify potential factors for inclusion in such a programme, appropriate for LMICs. Methods: Applying a Delphi method, 33 stakeholders (13 arthroplasty surgeons, 12 anaesthetists and 8 physiotherapists) from 10 state hospitals representing 4 South African provinces identified and prioritised i) risk factors associated with poor outcomes, ii) perioperative interventions to improve outcomes and iii) patient and clinical outcomes necessary to benchmark practice for patients scheduled for primary elective unilateral total hip and knee arthroplasty. Results: Thirty of the thirty-three stakeholders completed the 3 months Delphi study. The first round yielded i) 36 suggestions to preoperative risk factors, ii) 14 (preoperative), 18 (intraoperative) and 23 (postoperative) suggestions to best practices for perioperative interventions to improve outcomes and iii) 25 suggestions to important postsurgical outcomes. These items were prioritised by the group in the consecutive rounds and consensus was reached for the top ten priorities for each category. Conclusion: The consensus derived risk factors, perioperative interventions and important outcomes will inform the development of a structured, perioperative multidisciplinary enhanced patient care protocol for total hip and knee arthroplasty. It is anticipated that this study will provide the construct necessary for developing pragmatic enhanced care pathways aimed at improving patient outcomes after arthroplasty in LMICs.
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.

Browsing by Author "Marais, J."

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