Rapid Automated Quantification of Triacylglyceride Crystallinity in Molecular Dynamics Simulations

Abstract

The relative stability of crystalline polymorphs and the transition between crystalline and melt phases are key parameters in determining the physical properties of triacylglycerides used in food. However, while the determination of properties experimentally is well-defined, the ability to predict the onset of melting and discriminate between polymorphs is less well-defined within a molecular dynamics simulation environment. In this work, we present metrics for measuring the crystallinity, including a new metric, the near-neighbor occupancy time, giving a rapid determination of how many, and which, molecules are found in a crystal over a simulation trajectory, and the polymorphic determination of triacylglycerides over a simulation trajectory.

Predicting Lipid Eutectics Using Coarse-Grained Molecular Dynamics

“…The NNO is a quick method to determine whether the same molecules are within a cutoff distance of a given reference molecule in subsequent frames in an MD trajectory. If the same molecules are indeed found to be within this cutoff distance in subsequent frames, this indicates that the reference molecule is in a crystalline state, given the relatively short cutoff distance and the unchanging surrounding molecules, as shown previously . The NNO is calculated based on the central oleic bead, whose distance from the same beads on surrounding molecules should only change if the ordered crystalline structure is lost, except for the expected minor fluctuations.…”

“…The determination of the melting point of any binary TAG system was determined using a combination of methodologies described in previous work. , For any given simulation, the near-neighbor occupancy (NNO) was determined for the whole system over the full trajectory . The NNO cutoff distance between the middle oleic chain bead (bead 5 of the oleic chain) was set to 1.2 nm for all cases.…”

“… 18 , 22 For any given simulation, the near-neighbor occupancy (NNO) was determined for the whole system over the full trajectory. 22 The NNO cutoff distance between the middle oleic chain bead (bead 5 of the oleic chain) was set to 1.2 nm for all cases. The NNO was then summed for the whole system at each time point, reducing the dimensionality of the data from 3 to 2 and plotting the values versus temperature (assuming a perfectly linear increase in temperature along the whole trajectory, thus allowing for an easy time-to-temperature conversion).…”

Mathematical and computational modeling of fats and triacylglycerides

“…The most recent paper by this group has extended this methodology further to binary systems of sn ‐POSt, sn ‐POP, and sn ‐StOSt (Cordina et al., 2023c). Using similar methodology as in their previous paper to determine the melting point of a single TAG‐type crystal (Cordina et al., 2023a), the COGITO forcefield was tested to determine whether it could be used to determine the nonlinear behavior of such binary systems. The authors showed that, although the simulated melting points of the binary mixtures at various ratios were generally found to be lower than those determined empirically, the overall nonlinearity of the systems was reproduced well, such as the eutectic point of sn ‐POP/ sn ‐POSt at a 50:50 ratio and sn ‐POP/ sn ‐StOSt at a 80:20 ratio (Cordina et al., 2023c).…”

“…This paper was followed by another study by the same authors testing and showing the applicability of the COGITO forcefield to determine the melting points of pure TAG crystals. The authors employed a direct heating simulation method of pure TAG crystals with void defects, which enabled the accurate determination of the melting points of both short‐ and long‐chain TAGs, as well as unsaturated and saturated TAGs (Cordina et al., 2023a). This study again used the COGITO forcefield on TAGs, which had not been used for initial forcefield parameterization, further testing the robustness of the forcefield.…”