Determination of origin of South Tyrolean apples using Sr isotope ratio analysis: fundamentals and implementation

The origin of a food product is becoming increasingly important for consumers. One promising technique to prove the origin of agricultural products is the analysis of the strontium (87Sr/86Sr) isotope ratio. In crops, this ratio is generally related to the soil-geological features of the corresponding growing area. The present contribution summarizes some aspects of the 87Sr/86Sr ratio and its possible use as a geographical tracer for apples, investigated during a 3-year project. In a first experiment, we investigated the influence of agricultural practices and their external addition of strontium on the isotope ratio of apple trees under greenhouse conditions. The trees adapted slowly their 87Sr/86Sr ratio to that of the soil. The addition of tap water and fertilizers modestly influenced the 87Sr/86Sr ratio of the trees. In a second experiment, we investigated the 87Sr/86Sr ratio variability in terms of intra-part (difference between sub-samples of the same plant organ within a single tree), intra-tree (difference among the plant organs of the same tree) and inter-tree (differences between each plant-organ of different trees in the same orchard) variabilities and its relationship with the soil isotope ratio. The study was conducted in two orchards in South Tyrol. The intra-part and intra-tree 87Sr/86Sr ratio in both orchards showed a homogeneous distribution, but inter-tree we observed significant differences between the two orchards. As a third experiment, we extended our analysis to 41 orchards, distributed in North Italy. The 87Sr/86Sr ratio of apples with geographical indication were compared with those from non-protected districts. In both cases, the isotope ratio of the apples was highly correlated with the soil ratio of the corresponding orchard. However, areas having similar geological features were also characterized by similar ratios, and so a clear separation of all areas was not possible. This confirms the potential of the 87Sr/86Sr ratio as geographical tracer, but future studies should include other parameters, to improve the classification rate of agricultural products according to their place of origin