ABSTRACT
Reaction. Batch ethyl esterification of DHA was carried out at 30°C in a 20-to 100-mL screw-capped vessel with shaking at 130 oscillations/min. The first-step reaction was performed for 24 h in a vessel containing DHA/ethanol (1:1, mol/mol) and 2% immobilized C. antarctica lipase by weight of the reaction mixture. After the reaction mixture (0.1-1 L) was allowed to stand overnight, the resulting water layer was removed. The oil layer was then dehydrated for 45 min at 70°C and 5 mm Hg under a nitrogen stream. The second-step reaction was carried out at 30°C for 24 h in another vessel containing the dehydrated mixture from the first-step reaction, 5 molar equivalents of ethanol against the unesterified DHA, and 2% immobilized lipase by weight of the reaction mixture. The first-and second-step reactions were repeated by transferring the lipase into a fresh substrate mixture every 24 h.
