Building a database for provenance studies of origin wines from the Douro Valley

Abstract

AIM: The aim of the present work is to produce high quality analytical data suitable for evaluating the provenance of Port wine and Douro wine and integrating an authentic wine reference database. Both wines are produced within the same geographical area, the Douro Valley region located in the northeast of Portugal but follow different vinification procedures. The fermentation of Port wine is interrupted by the addition of a grape based spirit producing a sweet fortified wine typically consumed as digestif and dessert wine. Douro wine, on the other hand, is a table wine. The mineral composition of plants reflects the soil and the environmental conditions under which plants were grown. Minerals and trace elements, as well as some of their isotopes, are potential biomarkers in authenticity studies. We followed two analytical strategies, multielemental analysis and stable isotopes, to understand the parameters common to the region and fundamentally dependent on the soils and the ones influenced by processing methods or environmental contamination. MATERIAL AND METHODS: Fifteen samples of each type of wine, Port and Douro, were characterized for 26 elements. 7Li, 9Be, 11B, 27Al, 52Cr, 55Mn, 59Co, 60Ni, 65Cu, 66Zn, 75As, 77Se, 85Rb, 88Sr, 95Mo, 107Ag, 111Cd, 118Sn, 205Tl, 208Pb were determined by inductively coupled plasma mass spectrometer (ICP-MS) while Fe, Mg , P , Ca , Na , K were analysed by inductively coupled plasma optical emission spectrometer (ICP-OES). In addition, two isotopic systems were also studied: 87Sr/86Sr and 18O determined by Multicollector-ICP-MS (MC-ICP-MS) and Isotope Ratios Mass Spectrometry (IRMS), respectively. For all analysis reagents used were of high purity to prevent for contaminations. Ultra pure water of grade I, as defined in EN ISO 3696, was obtained using a Milli-Q plus Millipore System. Concentrated nitric acid, analytical grade (65%; Merck), was purified in the laboratory, using an acid distillation system (Milestone SubPUR), and compared to a commercial ultrapure nitric acid solution (Merck), on a routine basis. Analytical results were combined with chemometric tools, Principal Components Analysis (PCA) and Hierarchical Cluster Analysis (HCA), capable of performing multivariate data analysis. RESULTS: Ag, Cd and Tl were mostly below the level of quantification and were therefore removed from statistical analysis. 87Sr/86Sr varied between 0,71652 and 0,72290. PCA revealed 6 principal components that explained 84,6% of the total variance. CONCLUSIONS: The vinification method did not affect significantly stable isotopes, either 87Sr/86Sr or 18O. On the other hand, some elements; namely Cr, Co, Cu, Rb, Se, Ca and Na; showed significant differences between the two types of wine. The produced data can be integrated into an authenticity system for Port and Douro wines.The authors would like to thank the Porto and Douro wines Institute for providing the samples.Este trabalho foi desenvolvido com o apoio da FCT.N/