Crystallization of Femtoliter Surface Droplet Arrays Revealed by Synchrotron Small-Angle X-ray Scattering.

The crystallization of oil droplets is critical in the processing and storage of lipid-based food and pharmaceutical products. Arrays of femtoliter droplets on a surface offer a unique opportunity to study surfactant-free colloidlike systems. In this work, the crystal growth process in these confined droplets was followed by cooling a model lipid (trimyristin) from a liquid state utilizing synchrotron small-angle X-ray scattering (SAXS). The measurements by SAXS demonstrated a reduced crystallization rate and a greater degree of supercooling required to trigger lipid crystallization in droplets compared to those of bulk lipids. These results suggest that surface droplets crystallize in a stochastic manner. Interestingly, the crystallization rate is slower for larger femtoliter droplets, which may be explained by the onset of crystallization from the three-phase contact line. The larger surface nanodroplets exhibit a smaller ratio of droplet volume to the length of three-phase contact line and hence a slower crystallization rate.

Phytosterol crystallisation within bulk and dispersed triacylglycerol matrices as influenced by oil droplet size and low molecular weight surfactant addition.

Phytosterols can lower LDL-cholesterol and are frequently used by the functional food industry. However, little is known regarding how phytosterol crystallisation can be controlled, despite solubilised phytosterols having improved bioaccessibility. This study investigates phytosterol crystallisation in bulk milk fat and in model dairy emulsion systems at two average droplet sizes, 1.0 and 0.2 µm. The effect of lecithin and monoacylglycerol addition on phytosterol crystallisation for both emulsion and bulk systems was also evaluated. Results demonstrated that lecithin and monoacylglycerols enrichment into the bulk system minimised phytosterol crystallisation. However, in emulsions, phytosterol crystallisation was mainly influenced by decreasing the droplet size. Smaller emulsion droplets containing lecithin showed the greatest potential for decreasing phytosterol crystallisation and had improved physicochemical stability. This information can be employed by the functional food industry to minimise phytosterol crystallisation and possibly improve bioaccessibility.

Effect of Phytosterols on the Crystallization Behavior of Oil-in-Water Milk Fat Emulsions.

Milk has been used commercially as a carrier for phytosterols, but there is limited knowledge on the effect of added plant sterols on the properties of the system. In this study, phytosterols dispersed in milk fat at a level of 0.3 or 0.6% were homogenized with an aqueous dispersion of whey protein isolate (WPI). The particle size, morphology, ζ-potential, and stability of the emulsions were investigated. Emulsion crystallization properties were examined through the use of differential scanning calorimetry (DSC) and Synchrotron X-ray scattering at both small and wide angles. Phytosterol enrichment influenced the particle size and physical appearance of the emulsion droplets, but did not affect the stability or charge of the dispersed particles. DSC data demonstrated that, at the higher level of phytosterol addition, crystallization of milk fat was delayed, whereas, at the lower level, phytosterol enrichment induced nucleation and emulsion crystallization. These differences were attributed to the formation of separate phytosterol crystals within the emulsions at the high phytosterol concentration, as characterized by Synchrotron X-ray measurements. X-ray scattering patterns demonstrated the ability of the phytosterol to integrate within the milk fat triacylglycerol matrix, with a concomitant increase in longitudinal packing and system disorder. Understanding the consequences of adding phytosterols, on the physical and crystalline behavior of emulsions may enable the functional food industry to design more physically and chemically stable products.