The authentication of olive oil on the basis of hydrocarbon concentration and composition

Abstract

Samples of virgin olive oil and refined olive oil were analysed for n-alkanes by gas chromatography with flame ionisation detection to determine if the pattern and composition were oil specific and, therefore, if the hydrocarbon patterns could be used as determinants for assessing adulteration of olive oil. The carbon number profile of the extra virgin olive oil was unique inasmuch as the odd numbered predominance was not limited to two or three n-alkanes but started at tricosane (nC23) and continued to tritriacontane (nC33). The olive oil n-alkane data was added to an existing database that included rapeseed, safflower, sunflower, corn, palm, palm kernel, coconut, groundnut and soyabean oils and analysed by principal component analysis (PCA). Olive oil could clearly be differentiated from the other vegetable oils. PCA also allowed for the distinction of olive oils from different geographical regions. Authentic extra virgin olive oil was adulterated with various amounts of either crude sunflower or crude rapeseed oil, which resulted in adulteration levels between 0.5 and 11% w/w. Using the carbon number profiles alone it was possible to determine adulteration of the extra virgin olive oil with as little as 2.6% crude rapeseed oil or crude sunflower oil. Analysis of the n-alkane pattern by PCA made it possible to identify adulterants at levels as low as 0.5% w/w.