Acyl migration in enzymatic interesterification of triacylglycerols: Effects of lipases from Thermomyces lanuginosus and Rhizopus oryzae, support material, and water activity

The enzymatic interesterification of a solvent-free, equimolar mixture of trilaurin and 1,3-palmitin-2-olein was studied using three immobilized lipase preparations as catalysts. Analysis of triacylglycerol (TAG) content and fatty acid (FA) distribution monitored the lipase-catalyzed interesterification in sn-1,3 positions and FA exchange in the sn-2 position caused by acyl migration. Lipase from Rhizopus oryzae immobilized on polypropylene showed high sn-1,3 regioselectivity, and minimal exchange in the sn-2 position. With lipase from Thermomyces lanuginosus on silica (Lipozyme (R) TLIM), completely randomized FA distribution was obtained in 24 h. T. lanuginosus lipase on polypropylene caused a moderate rate of FA exchange in the sn-2 position. Thus, the T. lanuginosus lipase and silica promoted randomization of FA distribution, whereas the R. oryzae lipase and polypropylene did not. Higher water activity promoted hydrolysis and thereby increased concentrations of partial acylglycerols, but at the same time a decrease in the acyl migration rate of these intermediates was also observed. The net result was that at a certain degree of interesterification, there was no significant effect of water activity on the degree of exchange in the sn-2 position. On the other hand, a low water activity had the major advantage of giving a high yield of TAG.