engleski

Development of the analytical method for 87Sr/86Sr determination in olive oil

Olive tree (Olea europaea L.) is considered as one of the most important crops in the Mediterranean basin. Namely, its fruit is used in the production of olive oil which is a substantial part of the traditional diet. Olive oil, virgin olive oil in particular, is a very appreciated natural food product due to its beneficial effects to human health known for centuries. It has a specific taste, smell and flavor, with color varying from green to yellow, and it is consumed without being refined. Its healthy and beneficial properties depend on its composition, which varies widely depending on the fruit variety, degree of fruit ripeness, environmental conditions, production and storage process, as well as growing region i.e. its origin. European Union Member States agreed to obligatory origin labelling of extra virgin olive oils to prevent consumers being tricked about their true characteristics and origin (EC 182/2009). However, high commercial benefits in olive oil trade often lead to misleading statements and frauds about its origin. Fraud detection is a great challenge from an analytical point of view ; it implies searching for region-specific indicators such as isotopic, chemical or element composition patterns. Up to now, many analytical tools were developed with the purpose of discrimination of the olive oils’ geographic origin, such as analysis of volatile compounds, fatty acids and triacylglycerol composition, trace elements and stable isotopes of light elements. In addition, Sr isotope composition was also demonstrated as a reliable tool in the investigation of traceability and geographical origin of several food products, but has never been applied to olive oil due to the lack of the adequate analytical method. The determination of elements in olive oils is a big analytical challenge due to the complex matrix with high viscosity and high organic content as well as very low concentrations of trace elements, including Sr. In this work a sensitive and accurate analytical method for the determination of 87Sr/86Sr isotope ratio in olive oil by multicollector inductively coupled plasma mass spectrometer (MC-ICP-MS) was demonstrated. The method development consisted of: i) optimization of Sr extraction from the oil matrices and ii) optimization of the procedure for organic matter removal prior to Rb extraction on Sr-resin. Namely, the organic matter could hamper the Sr-resin extraction efficiency and influence the measurement of 87Sr/86Sr isotope ratio. In the first step, various extraction parameters such as different volume of extractant (8 M HNO3 and 2% HNO3 + 0.1% HCl) and sample were tested, as well as the performance of three different extraction procedure (ultrasonic, microwave and mechanical stirring). For the organic matter removal three different procedures were tested ; microwave and/or hot plate assisted digestion with concentrated HNO3 and H2O2, and dry ashing. Sr and Rb concentrations were measured to check for Sr mass balance and efficiency of Rb elimination. The Sr isotope composition was determined by MC-ICP-MS. The developed method was successfully applied for to the determination of 87Sr/86Sr isotope ratio in natural olive oil samples.

strontium isotopes ; olive oil ; pomace ; multicollector-ICPMS ; traceability

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