Abstract
Enzymatic production of a docosahexaenoic acid-rich oil from tuna oil creates considerable amounts of free fatty acids (FFA), which are treated as an industrial waste but the handling is difficult because of their solid state. We thus attempted to convert the waste FFA (Tuna-FFA) to their methyl esters through an organic solvent-free enzymatic process. When waste Tuna-FFA were esterified at 30°C with two molar equivalents of methanol (MeOH) using 1.0 wt% immobilized Candida antarctica lipase, the esterification degree reached 95% after 24 h. The reaction was recycled by transferring the enzyme into a fresh substrate mixture every 24 h, but the esterification degree maintained 95% during 45 cycles. To further increase the esterification degree, the esterification was repeated with 5 molar equivalents of MeOH against the remaining FFA after dehydration of the mixture obtained by the single reaction. The repeated reaction increased the esterification degree to 97-98%.
