Polymerisation and Oxidation of Docosahexaenoic Acid

Oils rich in polyunsaturated fatty acids, such as linseed oil, can oxidise to form polymers. These can be used as protective coatings and act as an alternative to those derived from petrochemicals. Such renewable source oils usually require the addition of metal ions as catalysts of the polymerisation process and/or the partial pre-oxidation of the oil before use. We hypothesised that increasing the unsaturation of the oil would result in polymerisation occurring without such requirements. Of the oils tested only docosahexaenoic (DHA) acid and boiled linseed oil (BLO) (which contains metal ion catalysts) demonstrated significant increases in viscosity during the incubation period, with both oils thickening at approximately the same rate. The production of the lipid peroxidation product propanal was much greater during DHA polymerization compared to that of BLO. DHA and BLO formed a water proof coating on cotton cloth although DHA formed more brittle coatings than BLO. Our results demonstrate that the greater extent of lipid peroxidation of high purity DHA allows it to polymerise in air to form a water resistant material similar to that obtained using boiled linseed oil but without the addition of toxic metal ion catalysts. Further investigation of this substance as a renewable component of coating materials may be warranted, particularly for applications requiring low toxicity such as those in contact with foodstuffs.