87 sr/ 86 sr ratio in vineyard soils from Portuguese denominations of origin and its potential for origin authentication

摘要

Aim: The control of geographical origin is one of the most challenging topics regarding wine authenticity. The aim of the present study was to assess the 87Sr/86Sr ratio of vineyard soils from Portuguese Denominations of Origin (DO) and evaluate its suitability as a tool for origin authentication.Methods and results: An analytical protocol was optimized (chromatographic separation of Sr and Rb, followed by inductively coupled plasma-mass spectrometry (ICP-MS) analysis) for 87Sr/86Sr isotopic ratio determination in soil-wine system. The 87Sr/86Sr ratios of soils from four vineyards located in three Portuguese DO (D?o, óbidos and Palmela), established on distinct soil types, were determined. Significant differences were found between soils of different DO regions. The soil in the D?o DO, developed on granites, showed a statistically higher 87Sr/86Sr ratio than the other soils, which were developed on sedimentary formations.Conclusion: The results show clearly that 87Sr/86Sr ratio may represent a suitable fingerprint for these Portuguese DO.Significance and impact of the study: This study highlights the relevance of setting up an international databank of 87Sr/86Sr values for use for geographical identification and authentication. IntroductionThe globalization of food markets has raised consumer concerns for product origin and quality. The place of origin of foodstuff is regarded as value-added information and as a guarantee of quality and authenticity. For wine in particular, geographical origin has a direct effect on its quality and commercial value, being one of the most studied products in terms of food authentication (Barbaste et al., 2002; Almeida and Vasconcelos, 2003).The control of the geographical origin of wine based on its chemical composition is one of the most challenging issues in relation to wine authenticity. In the last decade, many efforts have been made to identify potential markers and develop reliable analytical methods to determine the wine’s authenticity. Among these “fingerprints”, isotopic ratios play an increasingly important role (Almeida and Vasconcelos, 2001; Barbaste, 2001; Ferreira, 2008; Rosner, 2010). The application of methods using stable isotopes of light elements (H, C, N, O, S) started two decades ago, providing information on climate, distance from the sea, altitude, latitude, and technological practices (Ferreira, 2008).More recently, the study of isotopic ratios of heavy elements such as Pb and Sr came into use in this field of application, providing additional information on the geographical origin, since plants inherit the isotopic signature of these elements from the geological and pedological environment (Horn et al., 1993; Barbaste, 2001; Rummel et al., 2010).The use of Sr isotope ratio is a well established tool in earth sciences for dating and tracing the origin of rocks and minerals. Furthermore, some studies indicate that Sr isotope analysis could be very useful for determination and verification of the geographical origin of food.Sr has four naturally occurring stable isotopes with ranges of natural abundance as follows: 84Sr, 0.55-0.58%; 86Sr, 9.75-9.99%; 87Sr, 6.94-7.14%; and 88Sr, 82.29-82.77% (Berglund and Wieser, 2011). The 84Sr, 86Sr and 88Sr isotopes occur in constant relative proportions, while 87Sr gradually increases in minerals due to the radioactive β-decay of the 87Rb isotope. The relative abundance of 87Sr varies with geological ages and consequently with geographical locations, providing a fingerprint for different rock types (Capo et al., 1998; Vanhaecke et al., 1999; Almeida and Vasconcelos, 2001).The proportion of 87Sr to total Sr increases at a rate dependent on available Rb. Geological environments rich in Rb relative to Sr will have a high 87Sr/86Sr ratio, while regions with low Rb relative to Sr will retain low 87Sr/86Sr ratios for long periods of geological time. Therefore, the Sr isotopic composition of a geological sample depends on the Rb/Sr concentration ratio and age of the material.Weathering of the underlying rock and/or sediments is a significant source of strontium for the soil. Pre-Cambrian granitic bedrock and alluvial sands derived from felsic rocks show high 87Sr/86Sr ratios (0.710-0.716) reflecting the age of the continental crust and high Rb/Sr ratios from which these materials originated. Limestones have intermediate 87Sr/86Sr ratio values (0.706-0.709) and young oceanic basalts and their sediments show the lowest values (0.702-0.705) (Faure, 1986; Capo et al., 1998).Biological processes involved in plant metabolism do not significantly fractionate Sr isotopes (Capo et al., 1998). Elements are absorbed by the plants in the same isotopic proportions in which they occur in soil. Thus, plants reflect the growth environment, such as bedrock, soil and soil water content (Horn et al., 1993; Capo et al., 1998; Stewart et al., 1998), including all sources of Sr: natural (bedrock weathering, precipitation) and anthropogenic (e.g