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

Abstract

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® TL IM), 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.Practical applications: Both the type and the position of FA affect the properties of TAG. In TAG interesterification, there are thus different requirements for regiospecificity in FA exchange, depending on which product is desired. According to our results, lipase‐based catalysts can be used for TAG interesterification either to achieve unchanged FA composition in sn‐2 position or fast FA randomization in all positions. This helps to broaden the application of lipases in interesterification. The production of TAG can be tailor‐made for lipid mixtures with particular TAG composition and FA distribution using proper lipases, support materials, water activity, and reaction time.The enzymatic LLL–POP model reaction was used to investigate effects of lipase, support material, and water activity on acyl migration. (Fig. A): effect of Lipozyme® TL IM, TLPP and ROPP at aw 0.26, (Fig. B): effect of aw between 0.15 and 0.80 using Lipozyme® TL IM as the example.