REPOSITORY > RESULTS

Abstract

Increasing public awareness of food quality and safety has led to an increase in the demand for sensitive and reliable methods for the detection of food adulteration. Also, despite the numerous analytical techniques developed for the verification of food authenticity and provenance, it seems that stable isotope and elemental fingerprinting as well as DNA-based genetic methods are becoming increasingly important.
This doctoral thesis deals with milk and dairy products as an example commodity due to its high nutrient content and importance in the human diet, a high level of trade, growing competition in the market and the increasing complexity of supply chains. The main objective is the introduction and validation of specific methods in which a combination of different stable isotopic ratios of light bio-elements (2H/1H, 13C/12C, 15N/14N, 18O/16O, and 34S/32S), multi-elemental analyses, fatty acid profiles and real-time polymerase chain reaction (PCR) are exploited to determine the authenticity and provenance of Slovenian milk and dairy products. These parameters were used to establish the first database of authentic Slovenian cow, sheep and goat’s milk and cheese and to develop appropriate statistical models to differentiate milk according to geographical origin and to verify if the characteristics of milk or a dairy product on the Slovenian market corresponds to the label declaration.
The thesis consists of seven distinct, but closely interrelated, studies. In the first three studies, the main issues were to ensure the quality and comparability of elemental and isotopic composition data. The focus is on establishing appropriate protocols for the harmonization of methods and describes my role in an inter-laboratory assessment (CCQM-K140) of stable carbon isotope ratios in bulk honey and the development of food matrix reference materials, namely USGS82 to USGS91. The fourth study deals with the first systematic characterization of authentic Slovenian cow, sheep and goat’s milk and cheese based on stable isotope analysis and elemental composition to trace the origin of premium dairy products, which contribute to supporting the existence of Slovenian PDO cheeses. Regional discrimination of sheep’s milk was possible when taking into consideration the following elements P, S, K, Cl, Ca, and Zn content and the δ13C and δ15N values in casein. Further species differentiation based on discriminant analysis revealed that sheep and goat’s milk and cheese is distinguishable from cow’s milk with a predictive ability of 95.2%. The fifth investigation examines the use of stable isotopes and multi-elemental composition for the determination of the geographical origin of authentic cow’s milk from four geographical regions in Slovenia, namely Alpine, Dinaric, Mediterranean and Pannonian. This study revealed that it was possible to discriminate milk samples according to the production year, season and region based on discriminant analysis and that three Slovenian market samples fell outside of the acceptance criteria, i.e., they were mislabelled. The sixth investigation looks at using the fatty acid profile and the stable isotope composition (δ13C) of individual fatty acids for determining the authenticity (geographical origin) of Slovenian milk. The study revealed that differences in the fatty acid profile are more dependent on the year and season than on production region. It also shows that δ13C values in individual fatty acids are better biomarkers for studying metabolic transformation processes in ruminants than for discriminating between different production origins. The final part of this dissertation was dedicated to the verification of the authenticity of commercial dairy products from Slovenian market where molecular methods (real-time PCR) and fatty acid composition were used to determine the adulteration of dairy products. The results showed that real-time PCR could identify milk from different species if the content of cow's milk is >0.1% and provide a semi-quantitatively analysis when the content of cow’s milk is >0.5%. Real-time PCR also provided a rapid, robust and sensitive tool for the identification of adulterated sheep’s and goat’s milk cheese with cow’s milk. Moreover, differences in fatty acid composition meant that the adulteration of raw cow’s milk with <5% vegetable palm tallow was easily detected. On the Slovenian market, the most often mislabelled products were goat’s and sheep’s cheese with >20% not consistent with the declaration on the label.
In summary, this thesis shows the important role that stable isotope ratio analysis of light elements, multi-elemental composition as well as molecular methods (real-time PCR) and chromatographic analysis of fatty acids have on verifying the authenticity and geographical origin of not just milk and dairy products. The knowledge gained from this work is broadly applicable and as such, can be readily transferred to other commodities and production regions.