Characterization of the Nanoscale in Triacylglycerol Crystal Networks

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.