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Differentiation between geographic origins of wine using element composition
Phillip Minnaar* and Mardé Booyse**
Introduction
The chemical composition of wine is affected by a number of factors. These factors include production area, viticultural practices, grape variety, soil type, climate, yeasts and winemaking techniques. These factors play an important role in the characterisation and differentiation of wines. Differentiation of wine origin according to grape variety can be performed by determining parameters such as amino acids, polyphenols, element composition, isotope ratios and aromatic compounds (Aleixandre et al., 2002).
Trace elements [e. g. aluminium (Al), boron (B), barium (Ba), calcium (Ca), iron (Fe), magnesium (Mg), manganese (Mn)] and ultra trace elements [e. g. antimony (Sb), cadmium (Cd), mercury (Hg), selenium (Se), thallium (Tl)] have been studied to differentiate the geographic origin of wine (Latorre et al., 1994; Martin et al., 1999). The potential of multiple element analysis to determine the region of origin of wine was shown by McCurdy et al. (1992). Baxter et al. (1997) unequivocally identified the origin of Spanish and English wines from three different regions. Therefore the element composition of wines could be used to differentiate between geographical origins of varietal wines.
Various analytical techniques can be used to measure trace and ultra trace elements of wine, however, inductively coupled plasma atom emission spectrometry (ICP-AES) has been the most widely applied (Coetzee et al., 2005; Minnaar et al., 2005). The analysis of elements by ICP-AES, in particular sodium (Na), potassium(K), calcium (Ca), magnesium (Mg), manganese (Mn), lithium (Li), iron (Fe), copper (Cu) and lead (Pb), has been extensively employed as one of the most promising methods for classification of wine and wine authenticity (Coetzee et al., 2005; Minnaar et al., 2005).
The majority of studies are currently conducted in countries such as Spain, France, Italy and Greece, owing to their interest in wine authenticity. In South Africa, however, the regional differentiation between varietal wines of known origin by means of routine chemical analysis has not been addressed, except for recent studies by Coetzee et al. (2005) and Minnaar et al. (2005). There are certain measures, however, which are taken by Sawis (South African Wine Information and Systems) to ensure the authenticity of grape origin, grape variety and wine quantity in South Africa prior to certification (Liquor Products Act 60 of 1989). National authorities provide strict guidelines that must be adhered to with regard to wine quality, since the production of quality wines is of economic importance to South Africa. These guidelines include official tasting (organoleptic properties) and chemical analyses such as ethyl alcohol concentrations, sugar concentrations, sulphur dioxide levels (bound and free), pH and volatile acid determinations. Although these guidelines are strictly enforced and to a certain extent guarantee the quality of wine, they cannot be considered a substitute for chemical analyses to determine the origin of wine. The purpose of this study was therefore to investigate the use of element analysis by ICP-AES to differentiate between the geographic origins of Cabernet sauvignon and Sauvignon blanc wines produced in the Boland region of the Western Cape.
MATERIALS AND METHODS
Wine samples
Wine samples used in this study were market-ready Cabernet sauvignon (12 samples) and Sauvignon blanc (15 samples) wines. These single varietal wines were collected in 2000 and 2001, directly from estate wine cellars in sealed, labelled bottles. The samples were representative of the Paarl Valley (Franschhoek, Paarl, Wellington) and Stellenbosch region (Bottelary, Devon Valley, Jonkershoek).
Wine and statistical analyses
All wine samples were submitted for analysis of elemental composition using an ICP-AES technique. For further details, see Minnaar et al., 2005. The resultant data were analysed statistically by three multivariate techniques to reach the objectives of the project. Firstly, a technique was used to identify elements which have the most discriminating powers to differentiate between geographical origins (See Minnaar et al., 2005). Secondly, a technique was applied to give graphical representation of the groups (Cellars containing wines with element composition of similar discriminative powers) within geographical origins, and thirdly, a technique to identify the correctness of group classification was used to classify wine origins.
RESULTS AND DISCUSSION
Element concentrations measured for Cabernet sauvignon and Sauvignon blanc wines are listed in Table 1.
Graphical representation
The second statistical technique (canonical discriminant analysis) was used to give a graphical representation of results.
Cabernet Sauvignon
Canonical discriminant analysis was carried out considering the elements evaluated for Cabernet Sauvignon, with the graphical representation shown in Figure 1. The analysis shows the separation of five groups of wine cellars corresponding to geographical origins or localities. Magnesium and iron were responsible for the separation between geographic origins in the direction of the x-axis (Canonical variable 1). Potassium was responsible for the separation between geographical origins in the direction of the y-axis (Canonical variable 2). Jonkershoek and Wellington are distinguished by the x-axis (Can. 1). Franschhoek and Jonkershoek are distinguished from Wellington and Paarl by the y-axis (Can. 2).
Sauvignon blanc
Canonical discriminant analysis was carried out considering the elements evaluated for Sauvignon blanc, with the graphical representation shown in Figure 2. The analysis shows the separation of three groups of wine cellars corresponding to geographical origin or localities. Magnesium and boron were responsible for the separation between geographic origins in the direction of the x-axis (Canonical variable 1). Devon Valley is distinguished by the x-axis (Can. 1). Paarl and Devon Valley are distinguished from Bottelary by the y-axis (Can. 2).
To summarise, the graphical results clearly indicate the possibility of separating wines from different geographic origins using a selected subset of elements.
Classification according to geographical origins
A third statistical technique was used to identify the correctness of group classification according to geographical origins. The results are given in Table 2.
An average classification success of 76% for Cabernet sauvignon and 94% for Sauvignon blanc was achieved.
It is unclear as to whether the elements considered, although significant by the classification methods, represent the population of the region of origin, or only the random samples analysed. Examination of the data does allow a certain number of elements to be identified as common variables. Therefore, these results indicate that, under the prevalent conditions at the time of the study, with the limited number of samples, differentiation between geographic origins was possible using the element composition.
This study has illustrated that the chemical composition of wines of different grape varieties, and the geographic origin of the wine can be linked, even though viticultural practices and winemaking techniques vary between wine cellars. This implies therefore that viticultural practices and winemaking techniques do not have a definite influence on wine origin differentiation.
Conclusion
Visual examination of the element concentrations could not be used to differentiate between the origins. However, multivariate analyses were able to detect similarities between wines according to origin and by applying these statistical techniques, wine origins were separated using only magnesium, potassium, iron, boron and aluminium.
Magnesium, potassium and iron played the dominant roles in discriminating between geographical origins in Cabernet sauvignon wines. In contrast, boron, aluminium and magnesium were especially valuable for discriminating between Sauvignon blanc wines from different geographical origins.
As a small number of Cabernet sauvignon and Sauvignon blanc samples from a limited number of wine cellars were analysed, these findings should be regarded as preliminary results. A more comprehensive number of wine samples would facilitate the establishment of the element composition which is reproducibly influenced by the factors in vine growth, soil type and grape variety and elements that are not influenced at all.
For further information contact Phillip Minnaar at Nietvoorbij on (021) 809-3320 or minnaarp@arc.agric.za.
LITERATURE CITED
Aleixandre, J-L., Lizama, V., Alvarez, I. & Garc¡a, M. J., 2002. Varietal differentiation of red wines in the Valencian region (Spain). J. Agric. Food Chem. 50, 751 - 577.
Baxter, J. M., Crews, H. M., Dennis, M. J., Goodall, I. & Anderson, D., 1997. The determination of the authenticity of wine from its trace element composition. Food Chem. 60, 443 - 450.
Coetzee, P. P., Steffens, F. E., Eiselen, R. J., Augustyn, O. P. H., Balcaen, L. & Vanhaecke, F., 2005. Multi-element analysis of South African wines by ICP-MS and their classification according to geographical origin. J. Agric. Food Chem. 53, 5060 - 5066.
Latorre, M. J., Garcia-Jares, C., Mèdina, B. & Herrero, C., 1994. Pattern recognition analysis applied to classification of wines from Galicia (North-western Spain) with certified brand of origin. J. Agric. Food Chem. 42, 1451 - 1455.
Martin, G. J., Mazure, M., Jouitteau Martin, Y- L., Anguile, L. & Allain, P., 1999. Characterization of the geographic origin of Bordeaux wines by a combined use of isotopic and trace element measurements. Am. J. Enol. Vitic. 50, 409 - 417.
McCurdy, E., Potter, D. & Medina, M., 1992. Trace elements in wine. Laboratory News September, 10 - 11.
Minnaar, P. P., Rohwer, E. R. & Booyse, M., 2005. Investigating the use of element analysis for differentiation between the geographic origins of Western Cape wines. S. Afr. J. Enol. Vitic. 26, 53 - 63.
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