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Antioxidant Capacity of Pinotage Wines: Effect of selected viticultural and enological practices
Dalene de Beer, Elizabeth Joubert and Johann Marais, ARC Infruitec-Nietvoorbij, Stellenbosch
Background
Wine, as part of the Mediterranean diet, has gained a health-promoting image during the past few years due to the presence of phenolic antioxidants. The concept of "health through diet" is embraced by consumers in search of healthier lifestyles and overall well-being. Antioxidants have made the transition from obscure to highly "marketable", as consumers are becoming more aware of the possible health benefits afforded by dietary antioxidants. This has spawned new product development and/or improvements to the functional properties of existing products through new technologies and use of ingredients with high levels of compounds with putative health-promoting properties. The enhancement of red wine antioxidant capacity may therefore be of value in a competitive market environment. Increasing the concentration of polyphenols will increase the antioxidant capacity of wines (De Beer et al., 2003), but it can negatively affect flavour due to excessive astringency or bitterness (Preys et al., 2006). On the other hand, higher antioxidant capacity will increase the capacity of a wine to consume oxygen, preventing the negative impact of oxidation on the flavour and aroma of a wine.
The phenolic composition of wine is determined firstly by the phenolic composition of the grapes used for wine making (Ribéreau-Gayon et al., 1998), while sunlight exposure and temperature are the main factors influencing grape phenolic composition. These factors are mainly a product of the climatic area, but vine management practices also modify sunlight exposure and grape temperature by controlling the canopy microclimate. The second factor influencing wine phenolic composition is the extraction of phenolic compounds from the grape skins and seeds during maceration (Ribéreau-Gayon et al., 1998). Control of the maceration process is essential to ensure a good balance between the wine components.
In a previous study (De Beer et al., 2003; De Beer et al., 2005), commercial Pinotage wines were shown to have antioxidant capacity comparable to other South African cultivar wines. Pinotage wines have a unique phenolic profile with a higher content of malvidin-3-glucoside, procyanidin B1 and caftaric acid than Shiraz and Cabernet Sauvignon wines (Rossouw et al., 2004). The Pinotage cultivar was therefore selected to study the effects of viticultural (climatic and vine structure) and enological (cold maceration before fermentation and juice/skin mixing techniques during fermentation) practices on TAC, objective colour and phenolic composition.
Viticultural aspects
Several vineyard sites were selected in each of three climatic regions namely cool (area II), intermediate (area III) and warm (area IV) (Figure 1) and bush and trellised vine treatments were applied on each site during 2001, 2002 and 2003 (De Beer et al., 2006a). Grapes were harvested at approximately the same ripeness and wine prepared on small-scale at the ARC Infruitec-Nietvoorbij experimental cellar using a standard red wine procedure.
Trends for 2001 and 2002 wines in terms of TAC were the same with area IV resulting in wines with the lowest TAC, while no significant difference were found between wines from areas II and III (Figure 2). In 2003, climatic area had no effect on TAC. Similarly, only the colour saturation of 2001 and 2002 wines was affected by climatic area, with areas II and III in 2001 and area III in 2002 producing wines with the higher colour saturation (Figure 3). Higher colour saturation is generally associated with higher quality.
The trends for the effect of vine treatments on wine TAC over the experimental period were the same (Figure 4). A significant difference in wine TAC as a result of vine structure was only obtained in 2003, with bush vines producing wines with higher TAC than trellised vines. Vine structure did not affect colour saturation.
Climatic region and vine structure had significant effects on the content of several phenolic compounds, although trends for individual compounds differed between vintages. In some cases, a decrease in TAC could be explained by a decrease in individual polyphenols with high antioxidant activity. In other cases, the measured phenolic content could not explain changes in TAC indicating the role of unknown compounds and/or the impact of synergistic effects.
Enological practices
Experimental wines were prepared by using 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 in 2000 to 2002 (De Beer et al., 2006b).
Results for pre-fermentation maceration were not consistent between vintages, indicating the major impact that the initial grape phenolic composition has on the final product TAC. Differences in extractability of phenolic compounds between vintages could also play a role. Pre-fermentation maceration had very little effect on TAC, objective colour parameters and phenolic composition. The only consistent trend was that the vitisin A content of wine produced by pre-fermentation maceration at 15°C was higher than that of the control wine. Vitisin A, a pyranoanthocyanin, is formed during fermentation and is more colour stable than malvidin-3-glucoside. Improvement of wine quality when using pre-fermentation maceration treatments at 10°C was noted previously (Marais, 2003a).
Of the juice/skin mixing methods, pumping-over produced wines with lower TAC and total phenol content, as well as less favourable objective colour values than wines produced using the other two methods (Figures 5 and 6). This is possibly due to the fact that pumping-over is a much gentler mixing technique than punching-down and the rotor action. The punching-down or rotor treatment would therefore be preferred, especially since these two treatments give wines with higher sensory quality than those made by applying the pumping-over treatment (Marais, 2003b). Mixing at hourly intervals yielded a higher content of some phenolic compounds, such as quercetin-3-glucoside, gallic acid and caffeic acid, resulting in wines with higher TAC than those subjected to three hourly mixing intervals. This effect was only observed for the 2002 wines.
Conclusions
The treatments investigated caused definite changes in wine phenolic composition. These changes did not always coincide with changes in TAC. This discrepancy can be due to several reasons. Firstly, the different compounds have different antioxidant potencies, e.g. one compound with low potency can decrease, while another compound with high potency increased to give an increase in TAC. Secondly, only the major monomeric phenolic compounds were determined using HPLC, while many oligomeric and polymeric compounds are present which could not be quantified. Therefore, changes in phenolic composition for compounds not determined, including phenolic and non-phenolic compounds, can influence the TAC.
Acknowledgements
Financial support for the project by Winetech, NRF and THRIP is gratefully acknowledged. Our grateful thanks go to Drs Johann Marais and Marena Manley, as well as Danie van Schalkwyk and other personnel from ARC Infruitec-Nietvoorbij, for their inputs during the project.
For further information contact Dalene de Beer at Tel.: (021) 809-3449, Fax: (021) 809-3430 or E-mail: DBeerD@arc.agric.za
References
De Beer, D.; Joubert, E.; Gelderblom, W.C.A.; Manley, M. Antioxidant activity of South African red and white cultivar wines: Free radical scavenging. J. Agric. Food Chem. 2003, 51, 902-909.
De Beer, D.; Joubert, E.; Gelderblom, W.C.A.; Manley, M. Antioxidant activity of South African red and white cultivar wines and selected phenolic compounds: In vitro inhibition of microsomal lipid peroxidation. Food Chem. 2005, 90, 569-577.
De Beer, D.; Joubert, E.; Marais, J.; Manley, M. Climatic region and vine structure: Effect on Pinotage wine phenolic composition, total antioxidant capacity and colour. S. Afr. J. Enol. Vitic. 2006a, 27, 151-166.
De Beer, D.; Joubert, E.; Marais, J.; Manley, M. Maceration before and during fermentation: Effect on Pinotage wine phenolic composition, total antioxidant capacity and objective colour parameters. S. Afr. J. Enol. Vitic. 2006b, 27, 137-150.
De Villiers, F.S.; Schmidt, A.; Theron, J.C.D.; Taljaard, R. Onderverdeling van die Wes-Kaapse wynbougebiede volgens bestaande klimaatskriteria. Wynboer 1996, 78, 10-12.
Marais, J. Effect of different wine-making techniques on the composition and quality of Pinotage wine. I. Low-temperature skin contact prior to fermentation. S. Afr. J. Enol. Vitic. 2003a, 24, 70-75.
Marais, J. Effect of different wine-making techniques on the composition and quality of Pinotage wine. II. Juice/skin mixing practices. S. Afr. J. Enol. Vitic. 2003b, 24, 76-79.
Preys, S.; Mazerolles, G.; Courcoux, P.; Samson, A.; Fischer, U.; Hanafi, M.; Bertarnd, D.; Cheynier, V. Relationship between polyphenolic composition and some sensory properties in red wines using multiway analyses. Anal. Chim. Acta 2006, 563, 126-136.
Ribéreau-Gayon, P.; Dubourdieu, D.; Donèche, B.; Lonvaud, A. Red winemaking. In Handbook of Enology; John Wiley & Sons, Ltd.: Chichester, United Kindom, 1998; Volume 1, pp. 295-358.
Rossouw, M.; Marais, J. The phenolic composition of South African Pinotage, Shiraz and Cabernet Sauvignon wines. S. Afr. J. Enol. Vitic. 2004, 25, 94-104.
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