PURIFICATION OF DOCOSAHEXAENOIC ACID BY SELECTIVE ESTERIFICATION OF FATTY-ACIDS FROM TUNA OIL WITH RHIZOPUS-DELEMAR LIPASE

To purify docosahexaenoic acid (DHA), we attempted the selective ester ification of fatty acids originating from tuna oil with lipases. Tuna oil was hydrolyzed in NaOH-ethanol solution, and the resulting fatty a cid mixture [DHA, 23.2%; named tuna-free fatty acid (FFA)] was used as a starting material. Rhizopus delemar which acted lightly on DHA, was a suitable catalyst for the selective esterification of tuna-FFA, and lauryl alcohol was the best substrate. The reaction proceeded most ef fectively when a mixture of 2.4 g lauryl alcohol/tuna-FFA (2:1, mol/mo l), 0.6 g water, and 600 U Rhizopus lipase was incubated at 30 degrees C for 20 h with stirring at 500 rpm. Under these conditions 72% of tu na-FFA was esterified, and 84% of DHA was recovered in the unesterifie d fatty acid fraction. The DHA content in the fatty acid fraction rose from 23 to 73% with this reaction. To further elevate the DHA content , the unesterified fatty acids were extracted, and then esterified aga in under the same conditions. By this repeated esterification, DHA was purified to 89% with a recovery of 71% of its initial content.