Triacylglyceride melting point determination using coarse‐grained molecular dynamics

Abstract

This study is carried out using the COGITO force field to determine whether the thermodynamic melting point of pure triacylglyceride crystals can be predicted using molecular dynamics simulations. The triacylglycerides used in this study are both saturated and unsaturated, as well as symmetrical and asymmetrical, to test the robustness of both the force field and the direct heating methodology described in this paper. Given the nonequilibrium nature of a melting system, a larger number of simulations are required to ensure that the results are sufficiently converged, that is, with little fluctuation and a small confidence interval. The study also highlights the importance of the presence of defects, in this case as voids, to lower the melting nucleation energy barrier of the crystals and avoid superheating of the systems being tested. The size of these defects is much larger than what would be found in a physical crystal, however, the simple and robust procedure that was developed allows the accurate prediction of melting points of the different triacylglycerides.

Predicting Lipid Eutectics Using Coarse-Grained Molecular Dynamics

“…18,25 This methodology was tested on five different TAGs, including the TAGs being used in this study, with the simulated melting points being in very good agreement with the empirical melting points. 18 In this study, a similar methodology was employed to try and determine whether the known nonlinear behavior of binary TAG systems can be reproduced. By creating systems with a mixture of two TAGs, creating a crack void while retaining the ratio of TAGs as close as possible to that in the perfect crystal and heating this system, melting could be observed.…”

“…This is shown in Figure , where one can clearly see more space between the ends of the fatty acid chains where sn -POP is present. Given the importance of voids to lower the nucleation melting energy barrier during MD simulations, ,− ,, having an artificially created void (the crack void), along with the mini-voids created due to the differing chain lengths, leads to an amplified lowering of the energy barrier, which results in a lower-than-expected melting point.…”

“…18,25 Plotting the average melting onset temperature versus the void size in the crystal shows a clear decrease in the average melting point with increasing void size until a plateau is reached, followed by a sharp decrease in the melting point at larger void sizes, indicating the mechanical collapse of the system, with the melting point before the drop taken to be the melting point of the system. 18,25 This methodology was tested on five different TAGs, including the TAGs being used in this study, with the simulated melting points being in very good agreement with the empirical melting points. 18 In this study, a similar methodology was employed to try and determine whether the known nonlinear behavior of binary TAG systems can be reproduced.…”

“…Using the perfect binary TAG crystals, “crack” voids were generated to more closely represent reality and facilitate the melting onset. The description of these types of voids is given in our previous work . In all cases, the ratio of TAGs was kept to within ±1.5% (absolute) of the starting ratio in the perfect crystal, e.g., if the perfect crystal consisted of 10% sn -POSt and 90% sn -StOSt, then all the crystals with a crack void had a ratio of sn -POSt: sn -StOSt of 8.5–11.5%:91.5–88.5%.…”

“…In a previous study, we have shown that the melting point of various TAGs can be predicted using the using the COarse-Grained Interchangeable Triglyceride-Optimized (COGI-TO) 17 force field (FF). 18 In this study, we have extended this and investigated the nonlinear behavior of binary TAG mixtures of 1-palmitoyl-2-oleoyl-3-stearoyl-sn-glycerol (sn-POSt), 1,3-dipalmitoyl-2-oleoyl-sn-glycerol (sn-POP), and 1,3-distearoyl-2-oleoyl-sn-glycerol (sn-StOSt) using the same FF. These are the three main TAGs found in cocoa butter, and their nonlinear behavior has been studied extensively 8,[10][11][12]19 given their importance in the confectionery industry, thus allowing for an easy comparison of the simulated results with empirical data.…”