Global Small-Angle X-ray Scattering Data Analysis of Triacylglycerols in the α-Phase (Part II)

Abstract

The early stage crystallisation behaviour in a triacylglycerol mixture has been investigated on the nanoscale with a novel global small angle X-ray scattering analysis technique. This method has been tailored for the determination of the electron density profiles (EDP) replicating both, (i) the nanostructural texture of molten TAGs (refer to part I 'Global Small-Angle X-ray Scattering Data Analysis of Triacylglycerols in the Molten State' of this publication series), and (ii) the lamellar structure of the metastable-polymorph. In a first stage, the-phase scattering contribution alone was examined by classical Fourier analysis as well as by globally fitting the data, leading to practically identical EDPs. Based on these findings, we extended our analysis to the entire X-ray scattering contribution arising from molten TAGs and the solid-phase fraction. Remarkably, the experimental and theoretical data agree very well, providing for the first time a detailed nanostructural understanding about the coexisting molecular assemblies. This allowed in turn, also to quantitatively determine the solid fat content (SFC) with X-ray scattering data. Our new theoretical approach for measurement of SFC is based on the global analysis of small angle scattering/diffraction patterns and the SFC-results are in good agreement with values obtained from other techniques such as NMR spectroscopy.

Early stages of fat crystallisation evaluated by low‐field NMR and small‐angle X‐ray scattering

“…In agreement with literature, the latter displays two crystallisation events, the first one reaching a plateau at about 8% after 40 min and the second one still displaying an exponential growth, starting at approximately an hour, similarly to the SFC data, reaching a fraction of 0.35, but without plateauing even after 2 hr. This solid fraction is smaller than the SFC measured by NMR, but still in good agreement with previous reports …”

“…More specifically, from our NMRD analysis (Figure ), we consider that the increase of R 1 at very low frequencies is related to ODFs, similarly to what has been observed previously in nematic and smectic phases . These ODFs could be explained in the light of our newly proposed model of the structured clusters of molten TAGs . Briefly, TAGs are thought to assemble in clusters immersed in an isotropic medium of TAGs from which some molecules start interacting with the outer fatty acids, thus creating an additional layer, or shell, which increases in coverage as temperature decreases.…”

“…This solid fraction is smaller than the SFC measured by NMR, but still in good agreement with previous reports. [7,37] From the FFC-NMR measurements, the R 1 values at frequencies between 0.01 and 10 MHz were plotted versus time (see Figure S3), confirming that frequencies below 1 MHz are the most sensitive to structural changes in CB. We note that the R 1 values at 10 MHz seem to display a slight decreasing trend; however, this is still within experimental error (Figure 3c, squares).…”

“…[22,43,44] These ODFs could be explained in the light of our newly proposed model of the structured clusters of molten TAGs. [33,37] Briefly, TAGs are thought to assemble in clusters immersed in an isotropic medium of TAGs from which some molecules start interacting with the outer fatty acids, thus creating an additional layer, or shell, which increases in coverage as temperature decreases. These clusters might begin to orientate once a crystallisation-inducing temperature (such as 22°C) is reached, generating some of the first lamellar structures.…”

Crystal Memory near Discontinuous Triacylglycerol Phase Transitions: Models, Metastable Regimes, and Critical Points

“…This phenomenon has been studied for linear polymers [10][11][12], as well as for cocoa butter [13] and fatty acids [14]. Those papers addressed questions regarding the role played by polymer selfand mutual-entanglement in the kinetics of memory effects.Recently, TAG crystallization has been studied [15][16][17][18]. Coexistence of solid and liquid state TAGs were reported [16].…”