Enrichment of docosahexaenoic acid from tuna oil via lipase-mediated esterification under pressurized carbon dioxide

•The pressurized CO2 was effective reaction medium for the enrichment of DHA via esterification of tuna oil fatty acid and ethanol.•DHA was enriched in residual fatty acid by discriminative characteristic of Lipozyme RM IM against DHA.•The pressurized CO2 prepared at 25 °C, and 8.3 MPa was the most effective.•DHA concentration and recovery yield at an optimum condition were 75.8% and 81%, respectively.

This study focused on the use of pressurized CO2 as a reaction medium for the enrichment of docosahexaenoic acid (DHA) from tuna oil fatty acids via lipase-mediated esterification. Of the three lipases tested, Lipozyme RM IM from Rhizomucor miehei was selected for further study. Enzyme loading, water addition, and reaction time were also explored. Near-supercritical CO2, prepared at 25 °C and 8.3 MPa, was the most effective reagent tested for enriching DHA from the residual fatty acid fraction. In addition to near-supercritical CO2, optimal conditions included addition of 0.2 wt% (based on total substrates) water, enzyme loading of 5 wt% (based on total substrates), and a reaction time of 18 h. The DHA concentration and recovery yield for the residual fatty acid fraction under these optimal conditions were 75.8 wt% and 81 wt%, respectively.

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