Dromedary milk fat: thermal and structural properties 1. Crystalline forms ohtained by slow cooling

The thermal and structural behavior of anhydrous dromedary milk fat (ADMF) was studied by a technique that allowed simultaneous time-resolved synchrotron X-ray diffraction as a function of temperature (XRDT) and high sensitivity differential scanning calorimetry (DSC). As the camel probably represents the mammalian species best adapted to the hottest temperatures on earth as well as to harsh climatic conditions, the fatty acid composition of ADMF and its thermal properties are of special interest. In this paper, the first of a series, the crystalline organizations made by the triacylglycerols (TG) of ADMF during a slow cooling rate at \dT/dt\ = 0.1degreesC.min(-1) are addressed. The crystalline form obtained from about 29.5degreesC corresponds to a lamellar structure with a double-chain length longitudinal organization of the TG molecules (2L = 42.3 Angstrom) associated with a beta' lateral packing of the chains. The crystallization range which spreads over about 75-80degreesC, is similar to that observed for bovine milk fat, although the final melting temperature is higher by about 5-8degreesC. DSC scans revealed the existence of up to 6 exotherms on slow cooling. A similar complex behavior was also observed on heating. PEAK-FIT analysis of the XRDT individual patterns and their evolutions observed at small angles also showed the existence of additional molecular packings. However, XRDT analysis was unable to resolve individual structures. A possible epitaxy phenomenon during crystallization is discussed.