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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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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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Abstract  

Nutritional-physiological research of near past decades had established the real nutritional value of fats and oils. In the former theory the nutritional value of fats and oils is influenced mainly by the rate of saturated/unsaturated fats. It was ruled out, and positive, inert or risk physiological effect of every single fatty acid had been established. The health-care effect of omega-3 fatty acid mainly by the favourable (<3:1) rate of omega-6/omega-3 was established, as inert was concerned the saturated C16 fatty acid and the maximal amount of trans-fatty acids carrying health risk in fats was legally regulated in some countries. These nutritional-physiological requirements were mainly fulfilled by margarine producers and the elementary fats were selected in such a way that they should meet these requirements. Our method helps to the producers to quickly determine the amount of the liquid and solid fat at certain temperature and/or to adjust the technological temperature parameters. The main steps of our method are: a./ determination of cooling rate (K min–1) of the crystallizer device; b./ determination of the rate of liquid/solid fat at 10°C temperature. This value is used for the determination of the rate of fats and oils as a function of technology and required consistency firmness (spread ability); c./ determination of the temperature from the cooling curve where the crystallization of most part of the fat has finished. This value is used for the determination of outlet temperature parameter of product coming out from the crystallizer device for margarines or mixed-fat spreads with water-in-oil system.

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