Purification of Ethyl Docosahexaenoate through Selective Alcoholysis with Immobilized Rhizomucor miehei Lipase

Abstract

Ethyl docosahexaenoate (E-DHA) was efficiently enriched by selective alcoholysis of ethyl esters from tuna oil with lauryl alcohol (LauOH) using immobilized Rhizomucor miehei lipase. We thus attempted the development of an enzymatic process applicable to the industrial purification of E-DHA. The amount of LauOH was found the most important factor in the alcoholysis, and a larger amount of LauOH was effective for the enrichment of E-DHA. In this study, the amount was fixed at 7 molar equivalents for ethyl esters originating from tuna oil (E-DHA55; E-DHA content, 54.6mol%). A substrate mixture of E-DHA55/LauOH was introduced into a column packed with 8.0g of immobilized Rhizomucor lipase (22×63mm) at 30°C and a flow rate of 10mL/h (8.3g/h). E-DHA content increased to 87mol% with 58% alcoholysis. Even after 150 d, E-DHA content increased to 85mol%, although alcoholysis decreased to 48%. The half life of the lipase was determined as 150 d based on decrease in alcoholysis in the batch reaction. The reaction mixture flowing from the column was applied to film distillation, and unreacted ethyl esters were recovered in 82% yield. The ethyl ester fraction was contaminated with 2.4wt% LauOH and 6.3wt% lauryl esters, and lauryl esters could be completely removed by urea adduct fractionation. Through a series of purifications, E-DHA content was raised to 88wt% in 52% yield of the initial content in E-DHA55.