Effects of Crystal Growth and Polymorphism of Triacylglycerols on NMR Relaxation Parameters. 2. Study of a Tricaprin−Tristearin Mixture (original) (raw)
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Being able to determine the physical properties of fats such as polymorphism and crystal size is very important for the food industry. After a relationship was observed between spin-lattice relaxation time and crystal size in a solid-liquid mixture of triacylglycerols, the effects of polymorphism and crystal size were investigated by low-field NMR relaxation and powder X-ray diffraction on three binary mixtures of tricaprin and tristearin in the solid state. Second moment (M 2) was proven to be only sensitive to polymorphism. Its measurements permitted the quantification of polymorphic forms in a binary mixture, with a model based on M 2 of the pure components. As for the spin-lattice relaxation time (T 1), it was proven to be only sensitive to crystal size and not to polymorphism. Quantification was not possible with T 1 measurements, but information on the pattern of the crystal thickness distribution was obtained using the maximization entropy method algorithm. The determination of polymorphism was thus possible because of the difference in size between the R and β triacylglycerol crystals. Finally, a phase diagram mainly based on NMR data was constructed for the tricaprin/tristearin system.
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A rapid and accurate nlethod using nuclear magnetic resonance (NMR) spectroscopy is presented for determining the percentage of solids in fats and shortenings conditioned at selected temperatures or as received in the laboratory. This method provides more reliable information on the solids content of fatty materials than the empirical dilatometric solid fat index, and is applicable in the range of 50-100% solids which is beyond the limit of the official solid fat index method. The relationship between instrument response and actual solids present was determined on known nlixtures of liquid and solid triglyeerides. NMR and solid fat index (SFI) measurements were made on a series of commercial margarine oils of varying composition and consistency. Comparisons are presented giving the precision of the two techniques and the relationship between percentage of solids by the NMR technique and the solids fat index.
Biotechnology for Biofuels, 2015
Background: To identify and develop the best renewable and low carbon footprint biodiesel substitutes for petroleum diesel, the properties of different biodiesel candidates should be studied and characterized with respect to molecular structures versus biodiesel liquid property relationships. In our previous paper, 1 H low-field nuclear magnetic resonance (LF-NMR) relaxometry was investigated as a tool for studying the liquid-phase molecular packing interactions and morphology of fatty acid methyl esters (FAMEs). The technological potential was demonstrated with oleic acid and methyl oleate standards having similar alkyl chains but different head groups. In the present work, molecular organization versus segmental and translational movements of FAMEs in their pure liquid phase, with different alkyl chain lengths (10-20 carbons) and degrees of unsaturation (0-3 double bonds), were studied with 1 H LF-NMR relaxometry and X-ray, 1 H LF-NMR diffusiometry, and 13 C high-field NMR. Results: Based on density values and X-ray measurements, it was proposed that FAMEs possess a liquid crystal-like order above their melting point, consisting of random liquid crystal aggregates with void spaces between them, whose morphological properties depend on chain length and degree of unsaturation. FAMEs were also found to exhibit different degrees of rotational and translational motions, which were rationalized by chain organization within the clusters, and the degree and type of molecular interactions and temperature effects. At equivalent fixed temperature differences from melting point, saturated FAME molecules were found to have similar translational motion regardless of chain length, expressed by viscosity, self-diffusion coefficients, and spin-spin (T 2 ) 1 H LF-NMR. T 2 distributions suggest increased alkyl chain rigidity, and reduced temperature response of the peaks' relative contribution with increasing unsaturation is a direct result of the alkyl chain's morphological packing and molecular interactions. Conclusions: Both the peaks' assignments for T 2 distributions of FAMEs and the model for their liquid crystal-like morphology in the liquid phase were confirmed. The study of morphological structures within liquids and their response to temperature changes by 1 H LF-NMR has a high value in the field of biodiesel and other research and applied disciplines in numerous physicochemical-and organizational-based properties, processes, and mechanisms of alkyl chains, molecular interactions, and morphologies.
European Journal of Lipid Science and Technology, 2010
In this study, the crystallization and melting properties of four different fat blends with the same saturated fat content (30%) but with different ratios of symmetric and asymmetric monounsaturated triacylglycerols were investigated using pNMR, DSC and polarized light microscopy. Blends were either palmitic (P) or stearic (S) based, and were combinations of SatOSat-rich (Sat = saturated, O = oleic) and SatSatO-rich vegetable oils with high-oleic sunflower oil. The DSC results demonstrate that there was almost no difference in crystallization mechanism and crystallization rate between the two P-based blends. Both blends showed a two-step crystallization, which can be explained by polymorphism. Stop-and-return DSC results suggested an initial crystallization into an unstable polymorph followed by polymorphic transition during the crystallization. For the S-based blends there was a clear difference between the SOS-rich and the SSO-rich blend, with a slower crystallization for the SSO-rich blend. Possibly, this can be explained by fractional crystallization. The microstructure did not differ greatly between the blends. Directly after crystallization, the crystals of the SSO-rich blend were slightly larger than the crystals of the SOS-rich blend.
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Journal of Food Engineering, 2003
Triacylglycerols undergo solid-to-liquid phase transitions between ambient and body temperatures. This reversible feature is highly desirable for many fats as functional ingredients for foods, providing properties such as structure, mouthfeel, and flavor delivery. The objective of this paper was to study the interactions in binary and ternary mixtures of commercial hydrogenated fats. The following properties were determined: (a) crystal morphology, by polarized light microscopy at temperatures of 30, 35, and 40°C
International Journal of Food Properties, 2017
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Journal of Polymer Science Part B: Polymer Physics, 2018
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The polymorphic state of edible fats is an important quality parameter in fat research as well as in industrial applications. Nowadays, X-ray diffraction (XRD) is the most commonly used method to determine the polymorphic state. However, quantification of the different polymorphic forms present in a sample is not straightforward. Differential Scanning Calorimetry (DSC) is another method which provides information about fat crystallization processes: the different peaks in the DSC spectrum can be coupled to the melting/crystallisation of certain polymorphs. During the last decade, nuclear magnetic resonance (NMR) has been proposed as a method to determine, qualitatively and/or quantitatively, the polymorphic forms present in fat samples. In this work, DSC- and NMR-deconvolution methods were evaluated on their ability to determine the polymorphic state of cocoa butter, with XRD as a reference method. Cocoa butter was subjected to two different temperature profiles, which enforced coco...