Stable isotope ratios of carbon and hydrogen to distinguish olive oil from shark squalene-squalane

摘要

Squalene and its hydrogenated derivate squalane are widely used in the pharmaceutical and cosmetic fields. The two compounds are mainly produced from the liver oil of deep sea sharks and from olive oil distillates. Squalene and squalane from shark cost less than the same compounds derived from olive oil, and the use of these shark-derived compounds is unethical in cosmetic formulations. In this work we investigate whether ~(13)C/~(12)C and ~2H/~1H ratios can distinguish olive oil from shark squalene/squalane and can detect the presence of shark derivates in olive oil based products. The ~(13)C/~(12)C ratios (expressed as δ~(13)C values) of bulk samples and of pure compounds measured using isotope ratio mass spectrometry (IRMS) were significantly lower in authentic olive oil squalene/squalane (N: 13; -28.4 ± 0.5‰; -28.3 ± 0.8‰) than in shark squalene/squalane samples(N: 15; -20.5 ± 0.7‰; -20.4 ± 0.6‰). By defining δ~(13)C threshold values of -27.4‰ and -26.6‰ forolive oil bulk and pure squalene/squalane, respectively, illegal addition of shark products can be identified starting from a minimum of 10%. ~2H/~1H analysis is not useful for distinguishing the two different origins. δ~(13)C analysis is proposed as a suitable tool for detecting the authenticity of commercial olive oil squalene and squalane samples, using IRMS interfaced to an elemental analyser if the purity is higher than 80% and IRMS interfaced to a gas chromatography/combustion system for samples with lower purity, including solutions of squalane extracted from cosmetic products.