Effects of Triacylglycerol Molecular Species on the Oxidation Behavior of Oils Containing α-Linolenic Acid.

Two kinds of oils, pure perilla oil and a blend of perilla oil with palm oil, and their enzymatically interesterified oils having the same fatty acid compositions but with different compositions of triacylglycerol (TAG) species, were studied. In particular, the effects of TAG molecular species on the oxidation resistance of oils containing α-linolenic acid (Ln) were investigated. The content of TAG binding to three Ln molecules (3Ln-TAG) was found to be different between perilla oil (38.7%) and the interesterified oils (14.5-28.9%) , which were generated using Lipozyme RM-IM(®) (regiospecificity: sn-1, 3 positional). Oils with lower 3Ln-TAG contents were more stable to oxidation as determined by the conductometric determination method (CDM; 90°C, 20 L/h) than oils with higher 3Ln-TAG contents. This result was also supported by heating oxidation tests (180°C, 7 h) using the interesterified blended oils; the residual ratio of Ln-TAGs in the oils was found to be in the order of 3Ln-TAG<2Ln-TAG<1Ln-TAG. Oxidation stability of Lipase OF(®) (regiospecificity: random)-interesterified blended oils also improved on lowering the 3Ln-TAG content. In addition, the oxidation stabilities of Lipozyme RM-IM(®)-interesterified oils were slightly higher than those of the Lipase OF(®)-interesterified oils. We found that the content of 3Ln-TAG was almost the same in both oils, and the content of unsaturated fatty acid at the sn-1, 3 positions of Lipase OF(®)-interesterified oils was higher than that of Lipozyme RM-IM(®)-interesterified oils. These results indicate that oxidation stabilities of oils containing TAG with unsaturated fatty acid such as Ln at sn-2 position were higher than those having unsaturated fatty acids at the sn-1, 3 positions. From these results, the oxidation stability of oils rich in Ln, such as perilla oil and linseed oil, can be improved not only by decreasing 3Ln-TAG but also by enzymatically reducing the unsaturated fatty acid content at the sn-1, 3 positions.