Effect of acyl migration in Lipozyme TL IM-catalyzed interesterification using a triacylglycerol model system

Lipase-(Lipozyme TL IM) catalyzed interesterification of triacylglycerols was studied at water activities (a(w)) from 0.22 to 0.8. The substrates trilaurin (LLL) and 1,3-palmitin-2-olein (POP) were used in equimolar amounts to facilitate separate measurements of the interesterification in the sn-1,3 positions and changes in the fatty acid (FA) composition in the sn-2 position. The reaction at a(w) = 0.35 was the fastest, and that at a(w) = 0.84 the slowest, due to increased hydrolysis. The interesterification in the sn-1,3 positions was above 90% after 2 h reaction at a(w) = 0.22, 0.35, and 0.54, and the main triacylglycerols were LLP, POL, LOL, and PLP. The FA composition in the sn-2 position was conserved during the first 1-2 h, and the randomization due to acyl migration was complete after 24 h. During the entire reaction, FA present in the sn-1,3 positions were removed from the triacylglycerols by the enzyme, and a fraction of them was released by hydrolysis. The gradual change in the composition of the free FA thus reflected the randomization of FA within the triacylglycerol molecules. Improved knowledge on the factors affecting the rates of interesterification, hydrolysis, and randomization is required to develop tailor-made lipid products. Practical applications: In an ideal 1,3-specific lipase-catalyzed interesterification reaction, the FA composition in the sn-2 position remains constant. In practice, small changes are seen in the FA composition in this position, and under certain conditions a completely randomized FA distribution can be obtained. Randomization is slower than interesterification. Uncontrolled hydrolysis should be avoided because it lowers the TAG yield. By varying the reaction time, different triacylglycerol mixtures can be produced: i.e. products originating from 1,3-specific interesterification, as well as partially or completely randomized products