Investigation of the complex thermal behavior of fats - Combined DSC and X-ray diffraction techniques

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 degrees C and +80 degrees 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 beta-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 Angstrom, at the onset of lard crystallization might explain the difficulty of its fractionation.