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. 2021 Jul 27;10(8):1729.
doi: 10.3390/foods10081729.

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

Staša Hamzić Gregorčič  1   2 , Nives Ogrinc  1   2 , Russell Frew  3 , Marijan Nečemer  2 , Lidija Strojnik  1   2 , Tea Zuliani  1   2
Affiliations

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

Staša Hamzić Gregorčič et al. Foods. .

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.

Keywords: 87Sr/86Sr; cow diet; discriminant analysis; geographical origin; milk.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Geological map of Slovenia as indicated [31] with dairy farm locations (Table 1). The map was prepared by J. Vrzel.
Figure 2
Figure 2
Analytical protocol for effective Sr isolation from the sample matrix.
Figure 3
Figure 3
The 87Sr/86Sr isotope ratios in various dairy products from different countries, as reported in the literature. Horizontal dashed lines define the limits of the 87Sr/86Sr values measured in Slovenian milk of different geological regional origins, as indicated. References used for various dairy products worldwide: butter [24], cheese [27,30], and milk [29,30]. Dots on the vertical lines refer to the results obtained from the literature, whereas lines indicate the span of values. The 87Sr/86Sr isotope ratios in Slovenian truffles are also presented [39].
Figure 4
Figure 4
87Sr/86Sr ratios versus Sr concentrations in milk from different geological regions.
Figure 5
Figure 5
Relationship between 87Sr/86Sr ratios in rivers and milk. The line represents the 1:1 ratio indicating overlapping of the data.
Figure 6
Figure 6
Discriminant function score plot (a) and a discriminant loadings plot (b) for milk samples collected in 2014 on four different geological origins (1—Cretaceous: Carbonate Rocks and Flysch, n = 8; 2—Jurassic-Triassic: Carbonate Rocks, n = 15; 3—Neogene: Carbonate Rocks, Paleogene: Deposits, n = 17; 6—Quaternary: Deposits, n = 24).
Figure 7
Figure 7
OPLS-DA score plots and VIP values in the pairwise comparison between three different geological regions derived from all isotopic and elemental composition data of milk samples. (a) The ellipse on the score plot represents the 95% confidence interval. (b) The red-dotted line indicates criteria used to identify the variables for model development.
See this image and copyright information in PMC

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