Defining the physical properties of blends of acetyl-triacylglycerols derived from transgenic oil seeds

Abstract

Acetyl-TAG are unusually structured triacylglycerols (TAG) that possess an acetate group at their sn-3 position. Acetyl-TAG have different physical properties compared to regular TAG, including lower viscosity and improved cold temperature properties, making acetyl-TAG useful for different applications, including as a diesel replacement. These unusual TAG molecules can be synthesized in the seeds of transgenic plants through the expression of diacylglycerol acetyltransferase (DAcT) enzymes isolated from different Euonymus species. In this study, the kinematic viscosity as well as the crystallization and melting behavior of blends of acetyl-TAG and regular TAG were examined to define goals for acetyl-TAG synthesis in transgenic plants. Even small amounts of regular TAG when blended with acetyl-TAG had a disproportionate effect on the viscosity of mixture. This effect of regular TAG in increasing kinematic viscosity was more pronounced at lower temperatures. Under slow cooling conditions, the two different TAGs and their blends possessed two main crystallization events with different degree of separation of the thermal transition, and the lower crystallization temperature decreased with increasing amounts of acetyl-TAG in the blend. At higher cooling rates, one broad and tailed crystallization peak was observed. Heating thermograms indicate similar polymorphic behavior of the blends and a general peak shift to lower transition range with increasing acetyl-TAG compared to the two pure lipids. This information about the viscosity and thermal properties of blends of TAG and acetyl-TAG will provide useful targets for engineering higher levels of acetyl-TAG in transgenic seeds.