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-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| = 0.1 °C·min -1 are addressed. The crystalline form obtained from about 29.5 °C corresponds to a lamellar structure with a double-chain length longitudinal organization of the TG molecules (2L = 42.3 Å) associated with a β' lateral packing of the chains. The crystallization range which spreads over about 75-80°C, is similar to that observed for bovine milk fat, although the final melting temperature is higher by about 5-8 °C. DSC scans revealed the existence of up to 6 exotherms on slow cooling. A similar complex behavior was also observed on heating. PEAKFIT 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. Polymorphism / X-ray diffraction / differential scanning calorimetry / solid fat content / epitaxyRésumé -Propriétés thermiques et structurales de la matière grasse de lait de dromadaire. 1. Formes cristallines obtenues lors d'un refroidissement lent. Les propriétés thermiques et structurales de la matière grasse anhydre extraite du lait de dromadaire (ADMF) ont été étudiées par une nouvelle technique qui permet des mesures simultanées, sur un même échantillon, des signaux de microcalorimétrie différentielle à balayage (DSC) et de diffraction des rayons X en fonction du temps et de la température. L'étude des propriétés thermiques de la matière grasse du lait de chamelle, en relation avec sa composition, revêt un intérêt particulier si l'on considère les conditions

The thermal and structural behaviors of anhydrous goat's milk fat (AGMF) have been determined as a function of temperature using a powerful technique allowing simultaneous time-resolved synchrotron X-ray diffraction as a function of temperature (XRDT) and high-sensivity differential scanning calorimetry (DSC) measurements from the same sample. This first paper, aiming at the characterization of the physical properties of AGMF, we examine crystalline organizations made by triacylglycerols (TG) upon slow cooling at /dT/dt/ = 0.1 degrees C/min from 45 to -20 degrees C in order to approach system equilibrium. Three overlapped exotherms were observed by DSC upon cooling, whereas four endotherms were found on the subsequent heating at 1 degrees C/min. XRDT evidenced that AGMF crystallizes under four different lamellar structures, two with double-chain length packings at 41.5 and 38.2 angstroms and two with triple-chain lengths of 72 and 64.7 angstroms stacking. Simultaneous wide-angle XRDT has shown that initial nucleation mainly occurs in a packing of beta' type from approximately 26 degrees C, although some transient presence of alpha was detected. The absence of polymorphic transition, on heating, until final melting (approximately 40 degrees C) demonstrated the relative stability of the structures formed.

-The crystallization behavior of anhydrous dromedary milk fat (ADMF) was examined using Microcalix (Centre National de la Recherche Scientifique, Châtenay-Malabry, France), an instrument coupling time-resolved synchrotron X-ray diffraction as a function of temperature (XRDT) at both small and wide angles and high-sensitivity differential scanning calorimetry (DSC) at an intermediate (1 °C·min -1 ) and at a fast (5 °C·min -1 ) cooling rate from 60 to -20 °C, together with their subsequent melting at 1 °C·min -1 . Upon cooling at 1 °C·min -1 , the crystallization of ADMF started at about 24 °C with the formation of a lamellar structure with a 46.9 Å period corresponding to a double-chain length molecular stacking and hexagonal chain packing (2L 1 α). From 20 °C, a major crystalline species also with double-chain lengths of 42.5 Å and orthorhombic chain packing (2L 2 β') was observed. The successive crystallizations of varieties 2L 1 and 2L 2 were correlated with the apparition of two large exothermal events recorded simultaneously by thermal analysis (DSC). However, comparison of XRDT and DSC recordings revealed the presence of a third exothermal peak probably related to a transition α → β'. At fast cooling (5 °C·min -1 ) of ADMF, three crystalline varieties were formed: the 2L 1 α (47.6 Å), 2L 2 β' (42.15 Å) and a new crystalline structure with 4 chain lengths: 4L β' of period 84.5 Å, while three endotherms were recorded by DSC. This last crystalline form which had never been characterized until now, likely corresponds to the accumulation of defects in the stable 2L β' form (42.15 Å) resulting from fast cooling and then to a local lack of symmetry in the 4L cell along the c axis of the crystals. This lack of symmetry was released during a transition 4L → 2L observed upon heating. A polymorphic transition α →β' was always observed upon ADMF heating following cooling at either 5 or 1 ° C·min -1 . Compared with the slow cooling at 0.1 °C·min -1 which was studied in the previous paper of this series, ADMF presented different structural and thermal properties. Indeed, the cooling at 1 °C·min -1 and 5 °C·min -1 generated an unstable crystalline form (α) that was not found at slow cooling at 0.1 °C·min -1 . However, the major stable form 2L β' was always observed in the three types of cooling.polymorphism / X-ray diffraction / differential scanning calorimetry / camel's milk * Corresponding author ( ): michel.ollivon@cep.u-psud.frArticle published by EDP Sciences and available at http://www.edpsciences.org/lait or http://dx

Crystallization and melting properties of triacylglycerols (TGs) in anhydrous goat's milk fat (AGMF) are investigated by X-ray diffraction as a function of temperature (XRDT) coupled with high-sensitivity differential scanning calorimetry (DSC), using synchrotron radiation and Microcalix. The polymorphic behavior of AGMF was monitored by varying the cooling rates between 5 and 1 degrees C/min from 45 to -20 degrees C with their subsequent melting at 1 degrees C/min. Quenching of AGMF at -20 degrees C was also examined to determine the metastable polymorphic form of AGMF. At intermediate cooling rates, TGs in AGMF crystallize, from about 18 degrees C in two different lamellar structures with triple chain length 3Lalpha stacking of 72 A and a double chain length 2Lalpha stacking of 48 A, which are correlated to two overlapped exothermic peaks recorded by DSC. A reversible transition sub alpha <--> alpha was observed. Subsequent heating at 1 degrees C/min shows numerous structural rearrangements before final melting. At fast cooling of AGMF (5 degrees C/min), similar unstable crystalline varieties are formed while three endotherms are recorded. Several new unstable lamellar structures are observed after quenching. All of these data are compared to those previously reported at slow cooling (0.1 degrees C/min) showing a relative stability of the structures formed. In spite of general similitude, the thermal and structural behavior of the goat's milk is more complex than that of the cow's milk.