Olive oil adulterated with hazelnut oils: simulation to identify possible risks to allergic consumers
Résumé
To be labelled as “extra-virgin”, olive oil should be cold-pressed and may not contain refined oil or oil from other oleaginous seeds or nuts (Reg. EC 1531/2001). Adulteration of extra virgin olive oil (EVOO) with hazelnut oil (HAO) is a serious concern both for oil suppliers and consumers. The high degree of similarity between the two fats complicates the detection of low percentage of HAO in EVOO. Many analytical approaches have been developed during last years to trace HAO in EVOO, principally based on chromatographic analyses, differential scanning calorimetry and nuclear magnetic resonance. Adulteration of EVOO with HAO may introduce hazelnut-derived allergens. The aim of this work was to analyse the protein and allergen content of EVOO intentionally spiked with raw cold-pressed HAO or solvent-extracted HAO. SDS-PAGE analysis confirmed the presence of hazelnut proteins in solvent-extracted HAO with molecular masses ranging from 10-60 kDa. In contrast, cold-pressed HAO did not show traces of protein. In spiked EVOO, solvent-extracted HAO was still detected at 1% contamination level. Several bands on SDS-PAGE migrated at apparent molecular masses coinciding with known allergens like Cor a 1 (~17 kDa), Cor a 2 (~14 kDa), Cor a 8 (~12 kDa), oleosin (~17 kDa) and Cor a 9 (~60kDa). MALDI-TOF MS analysis confirmed the presence of two oleosin isoforms and of Cor a 9. Immunoblotting demostrated that an allergic patient with known reactivity to Cor a 1 and Cor a 2 indeed recognized a 17 kDa band in solvent-extracted HAO. In conclusion, we have shown that adulteration of extra virgin olive oil with solvent extracted hazelnut oil can be traced by simple SDS-PAGE analysis, and that such practice introduces a potential risk for hazelnut allergic patients.
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