Nanoscale characteristics of triacylglycerol oils: phase separation and binding energies of two-component oils to crystalline nanoplatelets

Abstract

Fats are elastoplastic materials with a defined yield stress and flow behavior and the plasticity of a fat is central to its functionality. This plasticity is given by a complex tribological interplay between a crystalline phase structured as crystalline nanoplatelets (CNPs) and nanoplatelet aggregates and the liquid oil phase. Oil can be trapped within microscopic pores within the fat crystal network by capillary action, but it is believed that a significant amount of oil can be trapped by adsorption onto crystalline surfaces. This, however, remains to be proven. Further, the structural basis for the solid-liquid interaction remains a mystery. In this work, we demonstrate that the triglyceride liquid structure plays a key role in oil binding and that this binding could potentially be modulated by judicious engineering of liquid triglyceride structure. The enhancement of oil binding is central to many current developments in this area since an improvement in the health characteristics of fat and fat-structured food products entails a reduction in the amount of crystalline triacylglycerols (TAGs) and a relative increase in the amount of liquid TAGs. Excessive amounts of unbound, free oil, will lead to losses in functionality of this important food component. Engineering fats for enhanced oil binding capacity is thus central to the design of more healthy food products. To begin to address this, we modelled the interaction of triacylglycerol oils, triolein (OOO), 1,2-olein elaidin (OOE) and 1,2-elaidin olein (EEO) with a model crystalline nanoplatelet composed of tristearin in an undefined polymorphic form. The surface of the CNP in contact with the oil was assumed to be planar. We considered pure OOO and mixtures of OOO + OOE and OOO + EEO with 80% OOO. The last two cases were taken as approximations to high oleic sunflower oil (HOSO). The intent was to investigate whether phase separation on a nanoscale took place. We defined an "oil binding capacity" parameter, B(Q,Q'), relating a state Q to a reference state Q'. We used atomic scale molecular dynamics in the NVT ensemble and computed averages over 1-5 ns. We found that the probability of the OOE phase separating into a layer on the surface of the CNP compared to being retained randomly in an OOO + OOE mix were approximately equal. However, we found that it was probable that the EEO component of an OOO + EEO mix would phase separate and coat the surface of the CNP. These results suggest a mechanism whereby many-component oils undergo phase separation on a nanoscale so as to create a transition oil region between the surface of the CNP and the bulk major oil component (OOO in the case considered here) so as to create the appropriate oil binding capacity for the use to which it is put.

Edible oil structures at low and intermediate concentrations. II. Ultra-small angle X-ray scattering of in situ tristearin solids in triolein

“…The combination of X-ray scattering and computer simulation on both the meso-and the nano-scale 13,43 offers the possibility to characterize fat industrial products and relate the structures formed, not only to their chemical composition but also to their processing conditions. A whole new field of structural characterization in the fat/oil area is therefore open for the understanding and further tailoring of fat nanocrystalline networks.…”

Quantification of the physical structure of fats in 20 minutes: Implications for formulation

“…Models which predict or identify aggregating structures can help in the interpretation of data. Pink and his group modelled the structures which could arise via CNP aggregation. They employed coarse‐grained models which assumed (a) that CNPs formed by cooling were essentially insoluble in the liquid oils.…”

“…Structural levels : Results from modelling and experimental observations found that changes to structural level 5, depend on the solids and oils used, not only on changes to the processing conditions. For example, samples with less than 20% SSS in OOO gave a mass fractal dimension structure according to DLCA which relaxed to give a mass fractal dimension according to RLCA .…”

Triglyceride nanocrystal aggregation into polycrystalline colloidal networks: Ultra-small angle X-ray scattering, models and computer simulation

“…(c) Recent models of TAGs using atomic scale molecular dynamics. The possibility that coating of CNP surfaces can take place on a nanoscale in oils which contain minority components was studied in [31].They considered a flat surface representing an SSS crystal in contact with two liquid oils, comprising approximately 90% OOO with either 10% elaidein-diolein or 10% olein-dielaidein. They used atomic scale molecular dynamics [33,34] at room temperature in the NVT ensemble, and compared the free energies of (i) random mixes of the two samples and (ii) samples in which the minority components were assumed to be in contact with the SSS surface with the OOO removed from contact.…”