Supplementation studies involving natural trans fatty acids: real technical challenges, actual solutions
Résumé
Growing evidence suggests that natural trans fatty acids should be distinguished from industrial ones, regarding their impact on human health. One trans isomer at a time should therefore be considered in nutritional studies. However, a high amount combined with an excellent purity of the corresponding isomer remains a challenge. This study aimed at providing means to overcome such issues. The purification of several grams of trans-palmitoleic acid (C16:1 n-7 trans, TPA) was considered in this study, starting from the cis-palmitoleic acid (C16:1 n-7 cis, CPA). Fatty acids were used as ethyl esters. Several sources of CPA were evaluated. The following means were critically assessed: Flash HPLC, urea complexation, and crystallization in solvent. Within each step, the purity was checked by GC-MS, and the best means was chosen. Macadamia nut was deemed as a reliable source of CPA, the other cis-C16:1 isomers being present in low amounts. Purification of CPA was best carried out using Flash HPLC. The isomerization of CPA to TPA was easily done. Removing as much CPA as possible from the CPA-TPA mix was best performed by crystallization in solvent, ensuring a 99%-purity of the final TPA product. Complementary means were used to get high amounts of highly purified-TPA. Not only ethyl esters were suitable for purification purposes, but they made the purity control by GC-MS easy. Provided the availability of the corresponding cis-isomer, our purification strategy can be applied to any trans monounsaturated fatty acid.