Purification of ethyl docosahexaenoate by selective alcoholysis of fatty acid ethyl esters with immobilized Rhizomucor miehei lipase

Ethyl docosahexaenoate (E-DHA) is efficiently enriched by the selective alc oholysis of ethyl esters originating from tuna oil with lauryl alcohol usin g immobilized lipase. Alcoholysis of ethyl esters by immobilized Rhizopus d elemar lipase raised the E-DHA content in the unreacted ethyl ester fractio n from 23 to 49 mol% in 90% yield. However, the content of ethyl eicosapent aenoate (E-EPA) was higher than the initial content. Hence we attempted to screen for a suitable lipase to decrease the E-EPA content, and chose Rhizo mucor miehei lipase. Several factors affecting the alcoholysis of ethyl est ers were investigated, and the reaction conditions were determined. When al coholysis was performed at 30 degrees C with shaking in a mixture containin g ethyl esters/lauryl alcohol (1:3, mol/mol) and 4 wt% of the immobilized R . miehei lipase, the E-DHA content in the ethyl ester fraction was increase d and the E-EPA content was decreased. By alcoholyzing ethyl esters in whic h the E-DHA content was 45 mol% (E-tuna-45) for 26 h, the E-DHA content was increased to 74 mol% in 71% yield and the E-EPA content was decreased from 12 to 6.2 mol%. To investigate the stability of the immobilized lipase, ba tch reactions were carried out continually by replacing the reaction mixtur e with fresh E-tuna-45/lauryl alcohol (1:3, mol/mol) every 24 h. The decrea se in the alcoholysis extent was only 17% even after 100 cycles of reaction . It was found that increasing the proportion df lauryl alcohol increased t he conversion of E-EPA to lauryl-EPA. When an ethyl ester mixture in which the E-DHA content was 60 mol% (E-tuna-60) was alcoholyzed for 24 h with 7 m olar equivalents of lauryl alcohol, the E-DHA content was raised to 93 mol% with 74% yield and the E-EPA content was reduced from 8.6 to 2.9 mol%.