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Authentication of Extra Virgin Olive Oil (EVOO) sometimes requires a panel of different tests and – with more sophisticated adulteration – a weight of evidence interpretation.  For more crude adulterations a single test is often enough.

One of the available tests is for fatty acids ethyl esters (FAEE).  These are more concentrated in lower quality oils (e.g.improperly stored or overripe), formed from ethanol which is a result of fermentation. EU legislation specifies a maximum 35 mg per kg FAEE concentration in EVOO.

FAEE concentration is officially measured using gas chromatography (GC) after recovery by silica gel column chromatography. While highly accurate, this method is complex, time-consuming, and relatively expensive.

This paper (purchase required) reports an alternative approach to FAEE measurement by using infra-red spectroscopy (FT-IR) with machine learning. A dataset of 170 olive oil samples with FAEE concentrations ranging from 1.81 mg/kg to 109.00 mg/kg were analysed using FTIR. Spectral data were preprocessed and used to train various regression models.

The authors report that the best performance was obtained with an XGBoost model. Explainable AI techniques (SHAP) enabled interpretation of the model and identification of spectral regions mostly associated with FAEE content.

They conclude that combining FT-IR spectroscopy with advanced ML models—particularly XGBoost—can effectively predict the concentration of FAEE.

Photo by Massimo Adami on Unsplash

A Belgian local newspaper has conducted a survey of 32 samples of branded Extra Virgin Olive Oil sold through major retail outlets iand supermarkets.  The brands include internationally-recognised household names.  The newspaper commissioned testing at expert laboratories.

Results are summarised in this press article.  20 of the 32 “Extra Virgin” samples failed to meet the specification standard of Extra Virgin Olive Oil (EVOO).  Although oil degradation over time could be a hypothesis in some cases, in other cases the analytical weight of evidence was that the oil was Lampeter (a lower grade of olive oil) or – in one case – adulterated with sunflower oil.

Investigations are continuing into suspected certification fraud in the upstream supply chain.

Energy-Dispersive X-Ray Fluorescence (EDXRF) is a cheap non-destructive technique to measure metal and mineral content, typically operated as a laboratory benchtop method.

In this study (open access), researchers at the European Commission Joint Research Centre used market samples of oregano that had been previously tested under the EU co-ordinated official control plan to investigate whether EDXRF could be used as a screening technique.  This was a serendipitous extension of the use of EDXRF for checking compliance with EU limits for copper contamination.  After a relatively simple sample preparation, they measured a panel of 36 metals and minerals.

They found that, at it simplest level, the ratio of copper-to-zinc was a good indicator of adulteration with olive leaves without any need for modelling statistics.  Once multivariate statistics were used, samples could also be classified by geographic origin.  This classification required 2-stage modelling (SIMCA then PLS-DA) to achieve full potential, and then was limited because the reference dataset was not sufficiently comprehensive in terms of countries of origin.

The researchers concluded that their work demonstrates that EDXRF is a suitable screening method to detect oregano adulteration with other species, and to authenticate the geographical origin of the product. The method is clean, cheap and has a high sample throughput because it does not require sample digestion. For those reasons, the approach is ideal to be used by control laboratories.

SIMCA allowed the authentication of the geographical origin of oregano. The performance of the authentication could be improved with a combination of SIMCA with PLS-DA that provides sensitivities and specificities higher than 90 %. However, a database well populated with results obtained with samples coming from all the main producing countries, would be needed.