Time domain reflectometry for the detection of blends of EVOOs with tailored soft-deodorized olive oils
Time Domain Reflectometry (TDR) is a well-known technique used in several fields: checking of discontinuities in electric lines, soil moisture determinations, dielectric characterization of food and non-food materials. TDR is based on the response of the matter to an electromagnetic step which takes time to cross and to be reflected, and changes its shape according to the chemical-physical and structural composition of the material. The smaller the sample the faster the electromagnetic step must be. Extra virgin olive oils (EVOOs) and soft-deodorized olive oils (sdOOs) are chemically different: e.g. they have a different content of Fatty Acid Ethyl Ester (FAEEs). The conventional analytical techniques for determining FAEEs are complex, time-consuming, and reagents requiring. In the Oleum context the possibility of determining the FAEEs content and discriminating among blends of EVOOs and sdOOs was explored by TDR. The used instrumentation was able to generate and acquire the waveform of steps with rising time in the order of some tens of picoseconds and, as a consequence, a probe for few ml of sample could be used. The shape of reflected signals was analysed by multivariate analysis: Partial Least Squares Regression (PLS) was used to build predictive models of the FAAEs content and PLS Discriminant Analysis (PLS-DA) was applied for discriminating between blends. FAEEs were predicted with a regression characterized by a coefficient of determination (R2) of around 0.81 and with a Root Mean Square Error (RMSE) in the order of a ten of mg/kg. Blends of EVOOs and sdOOs with FAEEs content higher or lower than a selected limit (35 mg/kg) were all correctly classified. Although the results obtained must be corroborated with confirmatory tests considering variables, such as temperature, which can have an influence on the accuracy, the technique seems promising, at least for a screening. Currently, TDR measurements, such as those here conducted, requires high-cost, multi-functional, generic instrumentation (e.g. an oscilloscope) and personnel skilled in electronic measurements and statistical data analysis; thinking about a market diffusion of an instrumentation for FAEEs determinations, it will certainly be necessary to combine devices and automate calibration procedures and analysis functions in a dedicated and not too expensive tool. The implementation and marketing of such device, of a cost around three thousand euro, for screening tests could be attractive to companies that manufacture analytical instrumentation.