Dromedary Milk Fat: Biochemical, Microscopic and Rheological Characteristics

et al. 2004

Lait

-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

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…Shortchain FA (C4-C12) are present in very small amounts in camel milk fat compared with bovine milk fat [1,3,6].…”

Section: Introductionmentioning

confidence: 99%

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

Karray¹,

Lopez²,

et al. 2004

Lait

“…Although data on the general composition of camel's milk is reported by several sources [3,11,12,26], data on the chemical and physical properties of anhydrous Dromedary milk fat polymorphism 435 dromedary milk fat (ADMF), which is the fat isolated from butter, are still scarce. ADMF is an essential nutriment in desert areas with a complex fatty acid composition [2,5,8], which has already been discussed in the first article of this series [9]. As observed for other fats and in the previous study [9], the coupling of X-ray diffraction (XRD) as a function of temperature (XRDT) and differential scanning calorimetry (DSC) is the best technique to characterize the structural and thermal behavior of ADMF [14][15][16][17][18][19][20][21]25].…”

Section: Introductionmentioning

confidence: 99%

Dromedary milk fat: thermal and structural properties 2. Influence of cooling rate

Karray¹,

Lopez

et al. 2005

Lait

-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

Crystallisation and melting properties of dromedary milk fat globules studied by X‐ray diffraction and differential scanning calorimetry. Comparison with anhydrous dromedary milk fat

Lopez

Karray²,

Euro J Lipid Sci & Tech

et al. 2005

Crystallisation and melting properties of triacylglycerols (TG) in dromedary milk fat (DMF) globules are studied by X‐ray diffraction (XRD) as a function of temperature coupled with high‐sensitivity differential scanning calorimetry (DSC), using synchrotron radiation. The crystallisation properties studied on cooling at ∣dT/dt∣ = 1 °C.min−1 from 60 °C to −8 °C show the successive formation of two double‐chain length (2L) lamellar structures: α 2L1 (46.7 Å) from 22 °C and β' 2L2 (41.7 Å) from 9 °C, which coexist until the end of the cooling process. These two types of crystals are related to the two exothermal peaks recorded simultaneously by DSC. The melting properties are studied on subsequent heating of DMF globules at dT/dt = 1 °C.min−1. The detailed analysis of the intensity and position of the XRD peaks recorded as a function of time shows that (i) the α 2L1 structure melts first, (ii) some TG from 2L1 melt and are incorporated again in the 2L2 structure, and (iii) the 2L2 structure melts with a final melting temperature over 44 °C. The influence of the dispersion of TG molecules in individual fat globules, with the presence of an interface with water, was determined by comparing their crystallisation behaviour to that of the same TG extracted from cream (anhydrous DMF) under the same experimental conditions. Results show that the same lamellar structures, α 2L1 and then β' 2L2, are formed on cooling in the dispersed and bulk states. However, crystallisation in the unstable α form is favoured in fat globules.