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Abstract  

The crystallisation properties of a mixture of triacylglycerols (TG), cocoa butter (CB) 75%/miglyol 25%, were investigated on cooling at 0.5 °C/min using differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The influence of (i) the dispersion of TG within nanoparticles stabilised by proteins, and of (ii) the presence of polar lipids were characterised. In bulk, crystallisation of TG successively occurred with a α 2L (49.3 Å) structure, then the formation of longitudinal stackings of 44.5 and 34.5 Å of β′ form was interpreted as co-crystallisation of TG from CB and miglyol. The dispersion of TG in nanoparticles of about 400 nm induced a higher supercooling and changed their crystallisation properties. The formation of α 49.2 Å and β′ 45 Å structures corresponded to the segregation of TG from CB in solid phases while TG from miglyol remained liquid. Phospholipids with saturated fatty acid chains affected the thermal properties of TG, which demonstrated their localisation at the surface of the nanoparticles. DSC and XRD revealed to be very sensitive and adapted methods to increase the knowledge about the mechanisms of crystallisation in emulsion.

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Investigation of the complex thermal behavior of fats

Combined DSC and X-ray diffraction techniques

Journal of Thermal Analysis and Calorimetry
Authors: G. Keller, F. Lavigne, C. Loisel, M. Ollivon, and C. Bourgaux

The thermal behavior of three ural fats (displaying very different composition), cocoa butter (CB)2, lard, and a stearin obtained from anhydrous milk-fat (AMF) fractionation, were studied by both DSC and X-ray diffraction as a function of temperature (XRDT). To perform temperature explorations between −30‡C and +80‡C, at rates identical to those used for DSC and ranging from 0.1 K min−1 to 10 K min−1, a new set of X-ray sample-holders, temperature-controlled by Peltier effect, has been developed. It is shown that the three more stable polymorphic forms of CB were easily characterized by either X-ray diffraction or DSC, and existence of two Β-3L forms was confirmed. On the contrary, the more complex polymorphism of lard and AMF required combined examination by DSC and XRDT and the brightness of the synchrotron source for studies at the highest heating rates. Quantitative analysis of the long spacings of XRDT recordings is invaluable for interpretation of thermal events. For instance, it was found that the simultaneous formation of two polymorphic forms, of apparent long spacing of 34 and 42 å, at the onset of lard crystallization might explain the difficulty of its fractionation.

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Abstract  

Polymorphism of trilaurin mixed with 4% of cholesterol was studied with a setup coupling calorimetry and phase characterisation by in-situ X-ray diffraction (Microcalix). Four polymorphic forms were identified. Monotropic and enantiotropic transitions were identified from the reconstruction of Gibbs free energy diagram which allows the control of trilaurin polymorphism.

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Abstract  

Trichlorofluoromethane (CCl3F) and water form clathrate hydrate which melts at 8.5 °C under atmospheric pressure. By DSC and X rays analysis we could distinguish between hydrate and ice formed in emulsion containing NaCl and show that quantity of hydrate formed and its dissociation temperature are dependent on solution concentration. The equilibrium curve hydrate-NaCl solution is displaced towards higher temperatures with respect to corresponding ice curve. Consequently solid–liquid equilibrium can not be established in presence of both solids. Growth of hydrate crystals at the expense of ice was evidenced. Role of salt in hydrate growth and ice melting is examined.

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Order-disorder transitions were investigated in native cassava starch at intermediate moisture contents (35 to 60% wt. water), using Differential Scanning Calorimetry (DSC) and dynamic Wide Angle X-ray Diffractometry (WAXS) with a synchrotron radiation source.

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Journal of Thermal Analysis and Calorimetry
Authors: M. Ollivon, G. Keller, C. Bourgaux, D. Kalnin, P. Villeneuve, and P. Lesieur

Abstract  

Coupling of time-resolved synchrotron X-ray diffraction at both small and wide angles with differential scanning calorimetry is a new technique that allows simultaneous characterization of thermal and structural properties of a sample. The apparatus, called Microcalix, works between –30 and +230C at scanning rates comprised between 0.01 and 20C min–1 with a high sensitivity in both measurements using a single sample of small volume (from about 1 to 20 μL). The last version of the instrument is designed for laboratory bench and conventional source but preferably with rotating anode or multilayered mirrors. Measurements under low pressure or under shear as well as recordings of isothermal evolution are also possible. The example of the study of polymorphism of a monounsaturated triglyceride (PPO) will be presented as an application.

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