Insights in the Structural Hierarchy of Statically Crystallized Palm Oil

Abstract

Palm oil (PO) is still widely used for the production of all types of food products. Due to its triacylglycerol (TG) composition, PO is semisolid at ambient temperature, offering possibilities for many applications. In order to tailor the fat crystal network for certain applications, it remains imperative to understand the structural build-up of the fat crystal network at the full-length scale and to understand the effect of processing conditions. In this study, PO was crystallized under four temperature protocols (fast (FC) or slow (SC) cooling to 20 °C or 25 °C) and was followed for one hour of isothermal time. A broad toolbox was used to fundamentally unravel the structural build-up of the fat crystal network at different length scales. Wide-angle and small-angle X-ray scattering (WAXS and SAXS) showed transitions from α-2L to β’-2L over time. Despite the presence of the same polymorphic form (β’), chain length structure (2L), and domain size, ultra-small-angle X-ray scattering (USAXS) showed clear differences in the mesoscale. For all samples, the lamellar organization was confirmed. Both cooling speed and isothermal temperature were found to affect the size of the crystal nanoplatelets (CNPs), where the highest cooling speed and lowest isothermal temperature (FC and 20 °C) created the smallest CNPs. The microstructure was visualized with polarized light microscopy (PLM) and cryo-scanning electron microscopy (cryo-SEM), showing clear differences in crystallite size, clustering, and network morphology. Raman spectroscopy was applied to confirm differences in triglyceride distribution in the fat crystal network. This study shows that both cooling rate and isothermal temperature affect the fat crystal network formed, especially at the meso- and microscale.

From Nucleation to Fat Crystal Network: Effects of Stearic–Palmitic Sucrose Ester on Static Crystallization of Palm Oil

“…The main fatty acids were 45.4 ± 0.1% palmitic acid (P), 38.4 ± 0.1% oleic acid (O), 9.3 ± 0.0% linoleic acid (L), 4.4 ± 0.0% stearic acid (S), 1.2 ± 0.0% myristic acid (M) and 0.3 ± 0.0% lauric acid (La). The solid fat content (SFC) was 48.0 ± 0.1% at 10 [32].…”

“…The SAXS data were further processed as previously discussed by De Witte et al (2024) [32]. The following parameters were obtained:…”

“…The beamline setup is described in detail by Narayanan et al (2022) [35]. The setup of the experiment is described in detail by De Witte et al (2024) [32].…”

“…The Scherrer equation or the Bertaut-Warren-Averbach (BWA) method can be used to assess the crystal nanoplatelet (CNP) thickness [32,34]. Due to incomplete polymorphic transitions, the measurements at 0 • C were excluded from the calculations.…”

“…With respect to the CNPs, De Witte et al (2024) [32] concluded, based on USAXS data, that for PO, a faster cooling rate and a lower isothermal temperature ensured the formation of smaller crystal nanoplatelets (CNPs). For FC25 and SC25, no differences were detected.…”