Continuous production of structured lipid containing gamma-linolenic and caprylic acids by immobilized Rhizopus delemar lipase

Production of a structured lipid containing gamma-linolenic acid (GLA) achi eved by the continuous acidolysis of borage oil with caprylic acid (CA) usi ng 1,3-specific Rhizopus delemar lipase as a catalyst. The lipase immobiliz ed on a ceramic carrier was activated by feeding the borage oil/CA (1:2, w/ w) mixture saturated with water into a column packed with the enzyme. Howev er, the generation of partial glycerides (20%) in the reaction mixture show ed that hydrolysis occurred concomitantly with acidolysis. The concomitant hydrolysis was completely repressed by feeding the oil/CA substrate mixture without adding additional water. When the substrate mixture was fed at 30 degrees C and a flow rate of 4.5 mL/h into a column packed with 8 g of the carrier with immobilized lipase, the content of CA incorporated in glycerid es was 50 to 55 mol%. The acidolysis activity scarcely changed even though the substrate mixture was continuously fed for 60 d; then it gradually decr eased. The CA content in glycerides was decreased to 73% of the initial val ue after 100 d, but returned to the initial level! when the flow rate was r educed to 3.1 mL/h. Molecular distillation was employed to separate the tra nsesterified oil from the reaction mixture. No glycerides were detected in the distillate, and the transesterified oil was recovered as the residue (a cid value, 2.6). Regiospecific analysis of the transesterified oil showed t hat only fatty acids at the 1- and 3-positions of borage oil were exchanged for CA. It was additionally found by highperformance liquid chromatography analysis that all the triglycerides contained one or two CA, and that the triglyceride with two GLA and one CA was also present, because the lipase a cted on GLA very weakly.