Abstract
Many food emulsions are stabilized by functional egg yolk biomolecules, which act as surfactants at the oil/water interface. Detailed experimental studies on egg yolk emulsifying properties have been largely hindered due to the difficulty in isolating individual chemical species. Therefore, this work presents a molecular model of an oil/water interfacial system where the emulsifier is one of the most surface-active proteins from the egg yolk low-density lipoproteins (LDL), the so-called Apovitellenin I. Dissipative particle dynamics (DPD) was here adopted in order to simulate large systems over long time scales, when compared with full-atom molecular dynamics (MD). Instead of a manual assignment of the DPD simulation parameters, a fully automated coarse-graining procedure was employed. The molecular interactions used in the DPD system were determined by means of a parameter calibration based on matching structural data from atomistic MD simulations. Despite the little availability of experimental data, the model was designed to test the most relevant physical properties of the protein investigated. Protein structural and dynamics properties obtained via MD and DPD were compared highlighting advantages and limits of each molecular technique. Promising results were achieved from DPD simulations of the oil/water interface. The proposed model was able to properly describe the protein surfactant behavior in terms of interfacial tension decrease at increasing protein surface concentration. Moreover, the adsorption time of a free protein molecule was estimated and, finally, an LDL-like particle adsorption mechanism was qualitatively reproduced.
Highlights
Food emulsions are made of a continuous water phase, a disperse phase with a high content of oil, and a surfactant that stabilizes the oil drops.[1,2,3,4,5] The droplet size distribution (DSD) is the most important property of the emulsion since the structure, stability, taste, and color of the final product depend on the DSD.[1,2,3,4,5] The DSD, in turn, depends on the emulsion composition, the type of process, and the operating conditions under which the production process operates.[6]
Using the molecular dynamics (MD) radial distribution functions (RDFs) as references, the Dissipative particle dynamics (DPD) RDFs were adjusted in order to best match curve heights and shapes by calibrating both aEV and rc of molecule bead pairs
Egg yolk is widely used as an emulsifier in many food emulsion preparations, little experimental research on the emulsifying scitation.org/journal/phf properties of its individual components has been carried out since their extraction and isolation from the egg yolk complex matrix turned out to be difficult
Summary
Food emulsions are made of a continuous water phase, a disperse phase with a high content of oil, and a surfactant that stabilizes the oil drops.[1,2,3,4,5] The droplet size distribution (DSD) is the most important property of the emulsion since the structure, stability, taste, and color of the final product depend on the DSD.[1,2,3,4,5] The DSD, in turn, depends on the emulsion composition, the type of process, and the operating conditions under which the production process operates.[6]. A typical mixing process is composed of two steps: first, the ingredients (mainly egg yolk, vinegar, oil, water, and salt) are mixed together in large stirred vessels at moderate rotational speed; this premixed emulsion is fluxed into a high-shear device, commonly a cone mill mixer, where the oil droplets undergo breakage until the final size distribution is reached.[3,4,5] This last step is crucial to fine-tune the DSD, in order to determine the properties of the final product
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