Fien De Witte

This study investigates the multiscale structure-function relationships in fat crystal networks with a focus into formulation, specifically examining the effects of concentration and purity on triglyceride (TAG) crystallization. For this, 10 different samples comprising stearic and palmitic saturated monoacid TAG systems at different concentrations (5%, 10%, 30%) and purities (pure standards vs. commercial sources) were examined. Using a combination of time-resolved synchrotron X-ray scattering (XRS), differential scanning calorimetry (DSC), and phase contrast microscopy (PCM), we assessed the structural evolution of monoacid saturated TAGs across nano-, meso-, and microscale levels. Findings show that concentration influences crystallization kinetics, degree of undercooling, and aggregate formation, with diluted systems favoring faster transitions and less dense networks. Purity also plays a key role, as pure TAG standards exhibit sharp, synchronized transitions, while commercial systems undergo slower crystallization, producing smaller, more compact flocs. These insights highlight the structural impact of formulation strategies commonly used in industrial fat blending.

The crystallisation of lipids in suspensions is influenced by the presence of the suspended material, in contrast to crystallisation in bulk lipids. In this research, the impact of carbohydrate particles on the crystallisation of palm oil was studied. Refined crystalline sucrose and glassy inulin were chosen as particulate materials added at a 10 wt% concentration. Suspensions were studied either without additives or together with sucrose ester (HLB 6) at a 0.5% concentration as dispersing agent. Suspensions were crystallized while cooling at 20 °C/min to 20 °C or 25 °C under static conditions. A multiscale analysis of the fat crystal network was conducted where simultaneous wide- and small-angle X-ray scattering were used to study the polymorphism, chain length stacking and crystal nanoplatelet (CNP) thickness. Ultra-small-angle X-ray scattering and cryo-scanning electron microscopy provided insights in the CNP size and shape. Polarized light microscopy and Raman spectroscopy revealed the microscale structure of the fat crystal network. Results show that both crystalline and amorphous particles act as surfaces for heterogeneous nucleation, facilitating nucleation. Polymorphic pathways and lamellar spacings remained unchanged, while CNP size decreased compared to crystallisation in the bulk lipids. The effects of the particle nature were subordinate to those of the dispersing agent.

In addition to being widely available and affordable, its semisolid nature at ambient temperature makes palm oil (PO) a popular ingredient for the food industry. This semisolid nature, consistent with the presence of a fat crystal network that entraps oil, is necessary to create food products that are technologically, sensorially, and nutritionally functional. The crystalline structure of lipids consists of a complex hierarchical structure, ranging from angstroms for polymorphic spacings, over nanometers for chain length structure and crystal nanoplatelet (CNP) sizes, to micrometers for CNP aggregates and flocs. To enable macroscopic lipid functionality, a deep understanding of the distinct structural levels and their interplay is a prerequisite. While X-ray scattering is ideally suited to study the smallest crystalline structures (polymorph, chain length, and CNP), microscopy is necessary to extend the characterization of the fat crystal network toward the microscale. This book chapter provides an overview of the latest insights into the microstructure development of PO using state-of-the-art techniques.

Advancements in Raman spectroscopy have broadened the utilization possibilities for food applications. The present review covers the working principle and methodology of the emerging technique in the context of wheat (flour) as a bakery ingredient. Special attention is paid to the primary constituents of wheat flour, starch and gluten proteins, both in their isolated forms and within complex matrices such as flour, dough, and various end products. This review examines how compositional and structural variations in these components are reflected in their Raman spectra and imaging characteristics and how this can be interpreted in terms of quality and functionality. The review concludes by outlining prospective research directions and future opportunities for advancing Raman-based analysis in cereal and bakery science.

Fat polymorphism plays a critical role in the structural and functional properties of fat-based food products. However, research on the polymorphism of monoglyceride oleogels remains limited. Previous work demonstrated the impact of composition and processing on the polymorphic transitions of monoglyceride oleogels, indicating that high shear and cooling rates accelerate β-polymorph formation. However, a detailed understanding on the effect of shear is still lacking. This research extends previous observations by using a CSS450 shear cell, allowing for precise control over cooling and shear rates. Two commercially available food-grade monoglycerides were mixed with rapeseed oil (10% w/w). Crystallization was performed with varying shear rates and analyzed with synchrotron radiation X-ray scattering techniques (SAXS and WAXS), differential scanning calorimetry and microscopy. The results showed that applying a low shear rate did not result in changes in the polymorphic transitions compared to static crystallization for both monoglyceride oleogels. However, increasing the shear rate resulted in the formation of the β-polymorph, even before the formation of the metastable sub-α polymorph. These findings provide new insights into the role of shear in monoglyceride oleogels, allowing for further optimization of fat structuring in food applications.

Time-resolved multiscale analysis of triglycerides during crystallization.

In this study six sucrose esters (SEs) with varying mono‐ester content, and thus varying hydrophilic‐to‐lipophilic balance (HLB) were studied. Wide‐ and small‐angle X‐ray scattering (WAXS and SAXS) was performed in order to unravel the nanoscale assembly of SEs. Differential scanning calorimetry (DSC) allowed to identify the melting and crystallization peaks of the different SEs, which could be attributed to the low and high esterified sugar molecules. Moreover, the results show clear differences in melting and crystallization behavior based on the type of fatty acid chains present. WAXS analysis unraveled a hexagonal subcell for all studied SEs. Despite some difficulty in identifying low intensity SAXS peaks, the analysis suggests a cubic structure for low HLB esters and a lamellar packing for high HLB esters. Medium HLB esters are hypothesized to contain a combination of the aforementioned structures.

In many food applications, the mechanical properties of fats play a critical role in determining the processing performance of fat-rich products. In fact, fat crystal networks form a particular class of soft materials that exhibit viscoelastic properties. The uniqueness of the mechanical response is intricately linked to the hierarchical nature of the system, as fats possess a complex architecture encompassing features at different scale levels (i.e., length scales). Since the discovery of crystalline nanoplatelets (CNPs), it has been hypothesized that CNPs are the basic building blocks of lipid networks and that CNPs are the responsible units for the mechanical properties of fats. This hypothesis, however, has only been partially tested. In this article, we examine which units could be responsible (e.g., lamellae, CNP, CNP aggregates) for the mechanical breakdown of fat crystal networks, through Rheo-USAXS in beamline ID02 (ESRF, Grenoble, France). Time-resolved USAXS profiles were acquired during the three steps of a three-interval thixotropy test (3iTT), namely, pre-shear, shear and recovery. The results were then utilized to evidence which specific length scale is arranged (i.e., orientated) during rheological breakdown. The findings suggest that, at the tested shear rates, orientation is only visible from 250 nm onwards, suggesting that the rheological breakdown of triglycerides is primarily driven by the orientation, and possible disruption, of CNP aggregates. These results reveal the critical role of CNP aggregates in the mechanical properties of fats. In the longer term, we believe this study will steer future research toward a more focused understanding of CNP aggregation and disaggregation dynamics.