Browsing by Author "Rapo, Aleksi"

The geographical origin of food can be determined by analyzing stable isotope ratios of hydrogen and oxygen from water samples that have been extracted from food matrices. A geographical gradient is formed from isotope ratios of water constituents, due to the small mass differences of the different isotopes, which can be also seen in the growing plants in certain regions. Finnish Food Authority has established a method for differentiating domestic and foreign strawberry samples, which uses a database that was created for Finnish strawberries. To produce a representative water sample from food, almost all of the water needs to be extracted from the matrix. The aim of this master’s thesis was to establish and optimize the extraction process of water from strawberry samples with a cryogenic vacuum extraction (CVE). The secondary objective was to test if isotopic values of Finnish strawberries differ from that of foreign strawberry samples and thus be used for determining the domesticity of strawberries. The performance of the cryogenic vacuum extraction procedure was confirmed with three validation tests which tested extraction effect on the sample’s isotope ratios of hydrogen and oxygen, cross-contamination between extraction units and suitable sample fixing materials. The optimization did not reach acceptable accuracy as there were no significant differences between the experimental runs for the Box-Behnken design (BBD). The reason showing ineffective modelling of the design remains unknown, especially as the response surface diagram shows clearly the optimal and minimal trends of the tested factors for δ2H. However, this was not so evident for δ18O. The ranges of tested factors may partly explain this discrepancy. Nonetheless, the differentiation of foreign and domestic strawberry samples was successful with principal component analyses. However, several factors concerning cryogenic vacuum extraction and water extraction in general, such as recovery of water, sample pretreatment, sample storage, different sample matrices and coextracted compounds as well as extraction parameters, need to be addressed in future studies.