Effects of selected substrate forms on the synthesis of structured lipids by two immobilized lipases

Two immobilized lipases, IM 60 from Rhizomucor miehei and SP 435 from Candida antarctica, were used to synthesize structured lipids (SL). Tricaprin and trilinolein were interesterified to produce SL that contained one linoleic acid per triacylglycerol molecule (SL1) and SL with two linoleic acids (SL2). SL1 and SL2 were separated by silver nitrate thin-layer chromatography according to their unsaturation, and the fatty acid at the sn-2 position was determined after pancreatic lipase-catalyzed hydrolysis of SL1 and SL2. With IM 60, 57.7 mol% capric acid and 42.3 mol% linoleic acid were found at the sn-2 position of SL1, while 43.3 mol% capric acid and 56.7 mol%. linoleic acid were at the sn-2 position of SL2. The fatty acid at the sn-2 position of SL1 with SP 435 as biocatalyst was 43.6 mol% capric acid and 56.4 mol% linoleic acid, while SL2 contained 56.6 mol% capric acid and 43.4 mol% linoleic acid. Different structural forms of the capric acid-containing substrate (triacylglycerol vs. ethyl ester) and different chainlengths of triacylglycerol were selected to study the substrate selectivity of lipases. Results indicated that SP 435 had some degree of preference for the triacylglycerol form (tricaprin), and IM 60 produced SL more rapidly and reached steady state faster with tricaprin as substrate than with capric acid ethyl ester. For chainlength selectivity, mol% of synthesized SL from tricaprin + trilinolein and tristearin + trilinolein were compared. SP 435 exhibited no apparent preference for either tricaprin or tristearin. However, IM 60 showed a more rapid reaction with tricaprin than with tristearin.