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Abstract

This dissertation examines two main topics. The first topic is focused on the potential of strontium (Sr) isotope analysis to characterise milk and truffles as selected food commodities, traditionally important for Slovenia. The 87Sr/86Sr ratio for determining the provenance of bovine milk and truffles originating from different regions of Slovenia has been applied for the first time. Previous studies included stable isotope analysis of light elements and multi-elemental composition to determine the geographical origin of milk and dairy products and the data of the Sr isotope ratios in milk can improve the verification of their origin.
Slovenia has a rich geological diversity making it an ideal setting in which to investigate the potential of the Sr isotope analysis. In pursuit of this, the range of bioavailable 87Sr/86Sr values in milk and truffles was established to create an isotopic database. Truffles are a good example where isotope ratios of Sr reflect directly that in the soil, while in milk the primary source of Sr is the cattle’s diet (feed and drinking water). While considerable variability of 87Sr/86Sr ratios found in milk reflects the substantial heterogeneity of the geological background of its origin, multi-element and multi-isotope approach using cross-validation of truffles resulted in a 77 % correct classification rate according to geographical origin and a 74 % correct classification rate for species. The results, although promising, cannot rule out possible inter-annual or annual variation of the Sr isotopic composition of milk. The underlying geologic complexity and presence of multiple Sr inputs (air, water), including commercial feeding regime of the cattle, can undermine the strength of the provenance assignment of milk. Overall, the results indicate the limitations and directions of the use of 87Sr/86Sr ratios as a tool in food authenticity and traceability. The 87Sr/86Sr ratio has the potential to distinguish between different milk production areas as long as these areas are characterised by geolithology and land use. Study performed on truffles also indicated significant variations in 87Sr/86Sr ratios connected to geology. Based on the preliminary results, it is hypothesised that the 87Sr/86Sr ratio is controlled by the carbonate fraction of soil, which makes Sr a helpful tool for tracing the origin of truffles grown in areas without limestone. Both studies show that 87Sr/86Sr ratios can be a powerful tool for determining the geographical origin of food originating from countries with more homogeneous geology, while any interpretation based on 87Sr/86Sr ratios can be challenging for countries with heterogeneous geology, such as Slovenia. To investigate broader geographical origin, the Sr method requires detailed knowledge of the geology and the land use.
The second topic examines the possibility to detect milk adulteration with water using lactose as an internal standard. Several experiments were prepared, where milk was diluted with different proportions of water and the lactose isolated according to the standard procedure. The procedure utilizes theδ18O value of the lactose extracted from milk in comparison to the waterδ18O value of the same milk sample. It has been found that theδ18O of lactose is correlated to that of theδ18O of the milk water and can be considered as a reliable internal reference.