REESTERIFICATION OF POLY-UNSATURATED FATTY-ACID CONCENTRATES

Abstract

Fatty acids of the n-6 series such as γ-linolenic acid (C18:3) and of the n-3 series such as α-linolenic (C18:3), stearidonic (C18:4), eicosapentaenoic (C20:5) and docosahexaenoic acid (C22:6) are of great nutritional interest. These acids can be obtained by urea fractionation in concentrated form from natural sources like blackcurrant seed oil, borage oil, evening primrose oil, linseed oil and fish oil, respectively. Certain dietary applications require a reesterification of these fatty acid concentrates with glycerol to triglycerides. Industrial scale methods of reesterification could not be applied as such for the present polyunsaturated fatty acid systems. Therefore reaction conditions had to be adapted to these highly sensitive substances. A one step reesterification method, using ZnCl2 as catalyst, was optimized for three different fatty acid concentrates composed of the above mentioned acids. Under the given reaction conditions, it could be observed that α-linolenic acid is much more sensitive to polymerization than γ-linolenic acid. Different purification methods of the crude triglycerides have been evaluated, obtaining best results by liquid chromatography methods, in particular with respect to decoloration of the final products.