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 com position), cocoa butter (CB)(2), lard, and a stearin obtained from anh ydrous milk-fat (AMF) fractionation, were studied by both DSC and X-ra y diffraction as a function of temperature (XRDT). To perform temperat ure explorations between -30 degrees C and +80 degrees C, at rates ide ntical to those used for DSC and ranging from 0.1 K min(-1) to 10 K mi n(-1), a new set of X-ray sample-holders, temperature-controlled by Pe ltier effect, has been developed. It is shown that the three more stab le polymorphic forms of CB were easily characterized by either X-ray d iffraction or DSC, and existence of two beta-3L forms was confirmed. O n the contrary, the more complex polymorphism of lard and AMF required combined examination by DSC and XRDT and the brightness of the synchr otron source for studies at the highest heating rates. Quantitative an alysis of the long spacings of XRDT recordings is invaluable for inter pretation of thermal events. For instance, it was found that the simul taneous formation of two polymorphic forms, of apparent long spacing o f 34 and 42 Angstrom, at the onset of lard crystallization might expla in the difficulty of its fractionation.