No abstract

Here we report on the characterization of the nanoscale in triacylglycerol crystal networks of edible fats. Blends of tristearin and triolein were prepared in proportions between 20 and 100% w/w to achieve a wide range of supersaturations. Crystal networks were subjected to mechanical disruption using isobutanol at 10 °C and visualized using cryogenic transmission electron microscopy (cryo-TEM). This method allowed the breakdown of spherulitic structures into their primary crystals: nanoplatelets of approximate sizes 150 × 60 × 30 nm to 370 × 160 × 40 nm depending on supersaturation conditions, and a length to width aspect ratio of 2.3. The method also allowed the visualization of bimolecular triacylglycerol lamellae within a cross-section of a nanoplatelet. The tristearin d-spacing (∼4.5 nm) and domain size (30−50 nm) of the (001) plane, by cryo-TEM and small-angle X-ray diffraction, agreed quantitatively. Scherrer analysis provided an accurate estimate of the cross-sectional thickness of the nanoplatelets and was linearly related to the length and width of the corresponding nanoplatelets, allowing in principle the use of small-angle X-ray diffraction as a rapid and accurate “nanocrystal sizer”. A pictorial representation of the hierarchical structure of a triacylglycerol crystal network is presented. This work opens up the possibility of nanomanipulation of the structure of fats to target specific physical properties and physiological response.

Cryogenic transmission electron microscopy and X-ray diffraction techniques were used to analyze the effect of crystallization conditions on the nanostructure of triacylglycerol crystal networks. Nanoplatelet size was strongly affected by composition and degree of supersaturation in the melt, as well as external fields during crystallization, such as cooling and shear rate. Chemical interesterification induced a decrease in nanoplatelet size, while increases in the solid mass fraction also resulted in a decrease in nanoplatelet dimensions. Fast cooling rates and crystallization under shear produced a significant decrease in platelet length, width, and thickness. This work opens up the possibility of judiciously engineering the nanoscale of fatstructured products in order to formulate products with specific functionalities including hardness, liquid oil binding, water vapor barrier properties, and metabolic response in humans.

This article reports on the effect of laminar shear on structural and mechanical properties of physical mixtures of fully hydrogenated soybean oil (FHSO) in soybean oil (SO). Blends were crystallized statically and under laminar shear rates of 30 and 240 s(-1) at different wall temperatures (-10, 0, 20 degrees C). The micro- and nanocrystalline structures were characterized using Polarized Light Microscopy (PLM), and Cryogenic Transmission Electron Microscopy (Cryo-TEM). Rheological analysis was used to determine changes in mechanical properties. Oil-binding capacity was analyzed through the measurement of the oil lost from the fat samples (OL). Shearing greatly affected the structure at the nano- and mesoscale. At low shear rates, blends displayed the largest increase in crystal size with an increase in wall temperature at both the nano- and mesoscale. On the other hand, at shear rates of 240 s(-1), the effect of crystallization temperature was observed only at the nanoscale since no changes in meso-crystal sizes were observed at different temperatures. Crystallization under laminar shear promoted the growth of spherical crystalline particles at the mesoscale, called here "solid-lipid meso-particles". Crystallization under higher shear rates led to the formation of a weak network with low oil-binding capacity and promoted the asymmetric growth of nanoplatelets. In statically crystallized blends, nanoplatelets had an aspect ratio of -2, while in sheared blends this value increased significantly. These results revealed the existence of critical shear rate values above which strong alterations in the structure of the solid crystalline network took place. Shearing also affected the material's strength. Laminar shear induced a decrease in elastic modulus and yield stress values which was more pronounced at higher shear rate-temperature combinations. Shear-temperature combinations were successfully used to structure fats at the nano and mesoscale.

Structural length scales within a fat crystal network, from TAG molecules packing into lamellae, crystalline nanoplatelets and fractal aggregates of nanoplatelets.