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Crystallisation and melting properties of dromedary milk fat globules studied by X‐ray diffraction and differential scanning calorimetry. Comparison with anhydrous dromedary milk fat
Author(s) -
Lopez Christelle,
Karray Nadia,
Lesieur Pierre,
Ollivon Michel
Publication year - 2005
Publication title -
european journal of lipid science and technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.614
H-Index - 94
eISSN - 1438-9312
pISSN - 1438-7697
DOI - 10.1002/ejlt.200501179
Subject(s) - differential scanning calorimetry , lamellar structure , crystallization , anhydrous , crystallography , chemistry , melting point , analytical chemistry (journal) , calorimetry , diffraction , dispersion (optics) , materials science , thermodynamics , chromatography , organic chemistry , physics , optics
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 2L 1 (46.7 Å) from 22 °C and β' 2L 2 (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 2L 1 structure melts first, (ii) some TG from 2L 1 melt and are incorporated again in the 2L 2 structure, and (iii) the 2L 2 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 2L 1 and then β' 2L 2 , are formed on cooling in the dispersed and bulk states. However, crystallisation in the unstable α form is favoured in fat globules.