The Provenance of Slovenian Milk Using 87Sr/86Sr Isotope Ratios.

Staša Hamzić Gregorčič,Nives Ogrinc,Tea Zuliani,Marijan Nečemer,Russell Frew,Lidija Strojnik

doi:10.3390/foods10081729

Abstract

This work presents the first use of Sr isotope ratios for determining the provenance of bovine milk from different regions of Slovenia. The analytical protocol for the determination of 87Sr/86Sr isotope ratio was optimised and applied to authentic milk samples. Considerable variability of 87Sr/86Sr ratios found in Slovenian milk reflects the substantial heterogeneity of the geological background of its origin. The results, although promising, cannot discount possible inter-annual or annual variation of the Sr isotopic composition of milk. The 87Sr/86Sr ratios of groundwater and surface waters are in good correlation with milk, indicating that the Sr isotopic fingerprint in milk is reflective of cow drinking water. The 87Sr/86Sr ratio has the potential to distinguish between different milk production areas as long as these areas are characterised by geo-lithology. Discriminant analysis (DA) incorporating the elemental composition and stable isotopes of light elements showed that 87Sr/86Sr ratio together with δ13Ccas and δ15Ncas values have the main discrimination power to distinguish the Quaternary group (group 6) from the others. Group 1 (Cretaceous: Carbonate Rocks and Flysch) is associated with Br content, 1/Sr and δ18Ow values. The overall prediction ability was found to be 63.5%. Pairwise comparisons using OPLS-DA confirmed that diet and geologic parameters are important for the separation.

Highlights

Proof of provenance has increased in relevance over the past decade because of its positive impact on food safety, quality and consumer protection per national legislation and international standards and guidelines
To overcome the lack of standard protocols for sample preparation and analysis needed to enable comparability of cross studies and data interpretation, a proposed method for the 87Sr/86Sr isotope ratio determination in milk was optimised within this work
Slovenia is a relatively small country covering a mere 20,273 km2 but boasts great diversity in complex geology, relief, hydrological systems, and vegetation. This diversity was not observed to the same extent in the analysed milk samples

Summary

Introduction

Proof of provenance has increased in relevance over the past decade because of its positive impact on food safety, quality and consumer protection per national legislation and international standards and guidelines. The 87Sr/86Sr isotope ratio, provides a unique and highly efficient geographical tracer for several types of food products such as asparagus [10], rice [11,12], tea leaves [13,14], coffee [15,16], orange juice [17], and wine [18,19,20] The authors of these studies highlighted two main applications of the 87Sr/86Sr isotope ratio: (i) to characterise the Sr isotope composition of a specific agricultural area, creating a valuable database for subsequently verify products cultivated in that area; and (ii) to discriminate with certainty different production areas of a specific product. To overcome the lack of standard protocols for sample preparation and analysis needed to enable comparability of cross studies and data interpretation, a proposed method for the 87Sr/86Sr isotope ratio determination in milk was optimised within this work. Our study aimed to determine the 87Sr/86Sr isotope ratio in milk using an optimised and validated analytical method and apply it to Slovenian milk samples originating from different geological regions to test its applicability in traceability studies

Sampling

Multi-Elemental Analysis Using EDXRF

Statistical Analysis

Strontium Isotope Ratio of Authentic Slovenian Milk

C1 C2 C2 C2 C3 C3 C3 C4 C4 C5 C5 J1 J2 J2 J2 J3 J3

Discriminant Analysis