FATTY-ACID SPECIFICITY OF RHIZOPUS-DELEMAR LIPASE IN ACIDOLYSIS

We investigated the fatty acid specificity of 1,3-positional specific Rhizopus delemar lipase in acidolysis using a randomly interesterified oil, of which the constituent fatty acid contents were approximately the same, as a substrate. Acidolysis was carried out at 30 degrees C w ith shaking in a reaction mixture containing caprylic acid (CA)/the ra ndomly interesterified oil (2:1, w/w) and the lipase immobilized on a ceramic carrier (4% of reaction mixture). The activity on each fatty a cid was experimentally determined as the ratio of the content of the f atty acid exchanged for CA to that of the fatty acid existing at the 1 (3)-position of the substrate oil, and regarded as the fatty acid spec ificity in acidolysis. The fatty acid specificity in hydrolysis was in vestigated by analysis of the composition of fatty acids liberated fro m the same randomly interesterified oil. The Lipase acted strongly on myristic, palmitic, palmitoleic, stearic, oleic, linoleic, and alpha-l inolenic acids, and moderately on arachidonic and eicosapentaenoic aci ds. The activities on these fatty acids relative to that on oleic acid were almost the same in acidolysis and hydrolysis. On the other hand, the lipase acted moderately on gamma-linolenic and docosahexaenoic ac ids in the hydrolysis, but only very weakly on these fatty acids in th e early stage of acidolysis. This shows that the fatty acid specificit y in acidolysis is stricter than that in hydrolysis. Since the kinetic s of acidolysis of borage oil, arachidonic acid-containing oil (TGA-25 ), and tuna oil could be easily predicted from the fatty acid specific ity in acidolysis, it was concluded that the specificity was accuratel y evaluated. In addition, the fatty acids at the 1(3)-position of bora ge oil and TGA-25 were completely exchanged for CA in a total of three cycles of the reaction, and the contents of fatty acids other than CA in the transesterified oils agreed with that at the 2-position of the oils. Therefore, it was shown that repeated acidolysis using the immo bilized 1,3-specific lipase could be applied to regiospecific analysis .