Quantitative Assessment of Triacylglycerol Crystallite Thickness by ¹H Spin-Diffusion NMR

Abstract

Properties and consumer appreciation of fat containing food products are greatly influenced by the growth of the fat crystalline domains and their morphology. Various analytical methods can be exploited to provide insight into the multilength scale microstructure of fat networks, but very few are able to discriminate structural features between different ways of processing fats. We selected in this work methods that highlight the mesostructure of fat crystalline systems. In this respect, 1H spin-diffusion NMR and XRD methods were employed to determine the fat crystallite thicknesses (crystalline domain size). This is the first attempt to quantify the mesostructure domains of triglyceride-based fat crystals by means of 1H spin-diffusion NMR experiments. The crystalline domain sizes determined by spin-diffusion NMR were found to be in good agreement with the crystallite thickness determined by the Scherrer analysis of the first order diffraction line from SAXS data. These results demonstrate the ability of the NMR technique to characterize the mesostructure of fats in a quantitative manner. This method is of particular interest for the structure analysis of fats, especially because of the possibility to quantify the size of the crystalline domains in diluted systems where scattering techniques struggle with the amount of diffracting material.

Global Small-Angle X-ray Scattering Data Analysis of Triacylglycerols in the Molten State (Part I)

“…The first X-ray diffraction experiments on TAGs were carried out by the pioneers Clarkson and Malkin in 1934 who were among the first to analyze the polymorphism of TAGs . TAG polymorphism has since been widely studied, applying various methods − such as microscopy, − infrared and Raman spectroscopies, − nuclear magnetic resonance, − differential scanning calorimetry, ,,− ultrasound measurements, − X-ray and neutron scattering methods, ,− and computer simulations. , We note that TAGsalthough overall nonpolar moleculespossess a slight amphiphilic character, for the glycerol backbone is moderately hydrophilic because of the partial charges of both the oxygen and carbon atoms of the ester bond, whereas the acyl chains are completely hydrophobic . Therefore, they undergo aggregation into ordered structures with repeat distances in the order of few nanometers.…”

Global Small-Angle X-ray Scattering Data Analysis of Triacylglycerols in the α-Phase (Part II)

“…Other studies mainly focus on the determination of the polymorphs present at different crystallization stages − but disregard the role of coexisting molten TAGs. An exception concerns the small-angle X-ray scattering (SAXS)-based work of Dewettinck et al., who fitted the diffuse X-ray scattering arising from the liquid state of TAGs with a Lorentzian distribution; however, this was done to only roughly estimate the liquid-to-solid phase ratio in any given diffraction pattern.…”

Multiscale assessment of food lipid structures

“…A particular advantage of spin-diffusion NMR over SAXD is that it can sense very thin fat crystal nanoplatelets which cannot be detected by SAXD. The potential of 1 H spin-diffusion NMR as a tool to measure crystal domain sizes in fat based food dispersions has recently been demonstrated (Voda, Den Adel, van Malssen, & van Duynhoven, 2017). In this study the magnetization of the crystalline nanoplatelets was selected using a double quantum (DQ) filter.…”

“…The non-invasive and almost real-time nature of SFC measurements allows for monitoring of lipid crystallisation and further crystal growth under shear and variable temperature conditions (Marangoni et al, 2011;Marangoni & Wesdorp, 2013). The crystalline mesostructure, from a few tens up to a few hundred nanometers, can be explored by 1 H spin-diffusion NMR (Voda et al, 2017). In application to the fat crystal systems this technique can provide the thickness of the crystalline domains ( Figure 1.4).…”