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

Abstract

AbstractEthyl docosahexaenoate (E‐DHA) is efficiently enriched by the selective alcoholysis of ethyl esters originating from tuna oil with lauryl alcohol using immobilized lipase. Alcoholysis of ethyl esters by immobilized Rhizopus delemar lipase raised the E‐DHA content in the unreacted ethyl ester fraction from 23 to 49 mol% in 90% yield. However, the content of ethyl eicosapentaenoate (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 Rhizomucor miehei lipase. Several factors affecting the alcoholysis of ethyl esters were investigated, and the reaction conditions were determined. When alcoholysis was performed at 30°C with shaking in a mixture containing 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 increased and the E‐EPA content was decreased. By alcoholyzing ethyl esters in which 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, batch reactions were carried out continually by replacing the reaction mixture with fresh E‐tuna‐45/lauryl alcohol (1:3, mol/mol) every 24 h. The decrease in the alcoholysis extent was only 17% even after 100 cycles of reaction. It was found that increasing the proportion of lauryl alcohol increased the 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 molar 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%.