Abstract
The purpose of this study was to efficiently and enzymatically synthesize the highly unsaturated fatty acid (HUFA) ethyl esters from fish oils and ethanol using an immobilized lipase. Fish oils, ethanol, and immobilized lipases were mixed in n-hexane and then incubated at 30 to 60°C with shaking at 150 rpm for 12 h. Among the immobilized lipases, Lipozyme IM derived from Rhizomucor miehei showed the highest yield of HUFA ethyl esters from fish oils. The optimal temperature for the ethanolysis was between 40 and 50°C. The water added to the lipase in the range of 0 to 10 wt% did not affect the yield of ethyl esters although the presence of over 15 wt% of water induced the hydrolysis. The yield of HUFA ethyl esters from fish oil reached approximately 95% after incubation for 6 h, while those from EPA-25 and DHA-25 were maximal after 12-h incubation. The yields of ethyl esters of EPA and DHA from fish oils were more than 95% and 52-71% after 12-h incubation, respectively. Ethyl esters synthesized from fish oils by an immobilized lipase contained fewer hydroperoxides and conjugated fatty acids than those synthesized by chemical method. This enzymatic method using an immobilized Rhizomucor miehei lipase could be very effective for the conversion of marine oils to their corresponding ethyl esters.
