Selective hydrolysis of borage oil with Candida rugosa lipase: Two factorsaffecting the reaction

A 46% gamma-linolenic acid (GLA)-containing oil was produced by selective h ydrolysis of borage oil (GLA content, 22%) at 35 degrees C for 15 h in a mi xture containing 50% water and 20 units (U)/g reaction mixture of Candida r ugosa lipase. The GLA content was not raised over 46%, even though the hydr olysis extent was increased by extending the reaction time and by using a l arger amount of the lipase. However, 49% GLA-containing oil was produced by hydrolysis in a reaction mixture with 90% water. This result suggested tha t free fatty acids (FFA) that accumulated in the mixture affected the appar ent fatty acid specificity of the lipase in the selective hydrolysis and in terfered with the increase of the GLA content. To investigate the kinetics of the selective hydrolysis in a mixture without FFA, glycerides containing 22, 35, and 46% GLA were hydrolyzed with Candida lipase. The result showed that the hydrolysis rate decreased with increasing CLA content of glycerid es, but that the release rate of CLA did not change. Thus, it was found tha t the apparent fatty acid specificity of the lipase in the selective hydrol ysis was also affected by glyceride structure. When 46% CLA-containing oil was hydrolyzed at 35 degrees C for 15 h in a mixture containing 50% water a nd 20 U/g of the lipase, GLA content in glycerides was raised to 54% at 20% hydrolysis. Furthermore, GLA content in glycerides was raised to 59% when the hydrolysis extent reached 60% using 200 U/g of the lipase. These result s showed that repeated hydrolysis was effective to produce the higher conce ntration of GLA oil. Because film distillation was found to be extremely ef fective for separating FFA and glycerides, large-scale hydrolysis of borage oil was attempted. As a result, 1.5 kg of 56% GLA-containing oil was obtai ned from 7 kg borage oil by repeated reaction.