Véronique Fournier a Frédéric Destaillats b Pierre Juanéda a Fabiola Dionisi b Pierre Lambelet b Jean-Louis Sébédio c Olivier Berdeaux a a INRA, UMR FLAVIC, Dijon, France b Nestlé Research Center, Vers-chez-les-Blancs, Switzerland c INRA, Clermont-Ferrand, France Thermal degradation of long-chain polyunsaturated fatty acids during deodorization of fish oil Long-chain polyunsaturated fatty acids (LC-PUFA) of the n-3 series, particularly eico- sapentaenoic (EPA) and docosahexaenoic (DHA) acid, have specific activities espe- cially in the functionality of the central nervous system. Due to the occurrence of numerous methylene-interrupted ethylenic double bonds, these fatty acids are very sensitive to air (oxygen) and temperature. Non-volatile degradation products, which include polymers, cyclic fatty acid monomers (CFAM) and geometrical isomers of EPA and DHA, were evaluated in fish oil samples obtained by deodorization under vacuum of semi-refined fish oil at 180, 220 and 250 7C. Polymers are the major degradation products generated at high deodorization temperatures, with 19.5% oligomers being formed in oil deodorized at 250 7C. A significant amount of CFAM was produced during deodorization at temperatures above or equal to 220 7C. In fact, 23.9 and 66.3 mg/g of C20 and C22 CFAM were found in samples deodorized at 220 and 250 7C, respec- tively. Only minor changes were observed in the EPA and DHA trans isomer content and composition after deodorization at 180 7C. At this temperature, the formation of polar compounds and CFAM was also low. However, the oil deodorized at 220 and 250 7C contained 4.2% and 7.6% geometrical isomers, respectively. Even after a deodorization at 250 7C, the majority of geometrical isomers were mono- and di-trans. These results indicate that deodorization of fish oils should be conducted at a maximal temperature of 180 7C. This temperature seems to be lower than the activation energy required for polymerization (intra and inter) and geometrical isomerization. Keywords: Deodorization, fish oil, geometrical isomerization, long-chain poly- unsaturated fatty acids, thermal degradation. 1 Introduction The nutritional importance of long-chain polyunsaturated fatty acids (LC-PUFA) has been well established. PUFA of the n-3 series, and especially eicosapentaenoic (EPA, 20:5 n-3) and docosahexaenoic acid (DHA, 22:6 n-3), have specific roles particularly in blood clotting [1], in the inflam- matory systems [2], in the functionality of the retina [3] and in the central nervous system [4]. Fish oils and marine prod- ucts are the major food sources of n-3 LC-PUFA. Fish oils have to undergo refining steps before their con- sumption or their utilization as food supplements. Refin- ing is usually divided into four steps: degumming, neu- tralization, bleaching and deodorization. The degumming step is usually applied only to vegetable oils. The last step is critical as it involves high temperatures (180–270 7C) that could give rise to side reactions [5]. Deodorization primarily removes undesirable volatile substances and converts the oil into a bland-tasting, odorless and color- less liquid. Therefore, this process improves the oil’s quality and stability. Less unsaturated fats and oils were deodorized successfully, but then this method was applied to polyunsaturated oil [6]. Nowadays, steam refining is the only large-scale practicable method used in the industry [6] and has been used for fish oil deodoriza- tion. However, its repercussion on the production of deg- radation products from LC-PUFA still needs to be eval- uated. Due to the occurrence of numerous methylene-inter- rupted ethylenic double bonds, LC-PUFA are unstable and heat treatment induces a number of chemical trans- formations (oxidation, polymerization, cyclization, geo- metrical isomerization and/or double bond migration) [7]. Although deodorization aims to remove undesirable compounds that affect the taste and the smell of fish oil, a simultaneous loss of valuable components could occur. For this reason, it is essential to be able to quantify deg- radation products in refined fish oils and to find deodor- ization conditions to prevent their formation during pro- cessing. Among the degradation products formed during heat treatment in the absence of air, polar compounds (mostly oligomers), cyclic fatty acid monomers (CFAM) and geometrical isomers (trans fatty acid isomers) are more likely to be produced. Correspondence: Olivier Berdeaux, UMR FLAVIC, INRA, 17 rue Sully BP 86510, 21065 Dijon Cedex, France. Phone: 133 3 80693540, Fax: 133 3 80693223, e-mail: berdeaux@dijon.inra.fr Eur. J. Lipid Sci. Technol. 108 (2006) 33–42 DOI 10.1002/ejlt.200500290 33 Research Paper  2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.ejlst.com