33-1 |
Use of calorimetry and x-ray diffraction to study lipid polymorphism |
M. OLLIVON, Université Paris-Sud, Chatenay-Malabry, 92296, France, C. Lopez, Université de Paris-Sud/ARILAIT, 5 rue J. Clément, Chatenay, 92296, France, and C. Loisel, University of Paris-Sud/Danone, UMR8612, 5 rue JB clément, Chatenay, 92296, France. The polymorphism of lipids make the study of thermal and structural properties of fat-containing food products difficult. Such properties are dependent on sample history and determined using Differential Scanning Calorimetry (DSC) and X-ray diffraction techniques. Phase and polymorph identification are difficult due to the closeness of transition temperatures. A new instrument combining time-resolved synchrotron X-Ray Diffraction at both wide and small angles as a function of Temperature (XRDT) and high sensitivity DSC, in the same apparatus at scanning or isothermal modes over -30 +150°C was developed. This technique is regularly used on the D22 and D24 lines of DCI synchrotron of LURE, as well as at ELETTRA (Trieste) and at ESRF (Grenoble) to examine polymorphism of lipids in food and biological products. The coexistence of two solid and one liquid phase was established for cocoa butter (CB) at room temperature. Both solid phases which were characterized on CB by XRDT, DSC and by rheological measurements, show their own independent polymorphism. A liquid crystalline phase is also identified in CB as well as in palm oil. The time- and temperature-dependent thermal and structural behavior of milk fat are compared to that observed within the fat globules of dairy emulsions. Up to four different crystal types can be identified and formation and evolution of crystals are determined quantitatively as a function of temperature. The polymorphic evolution is shown to be slower in fat globules compared to that in bulk. The fat may act as a reporter of the nucleation induced by emulsifiers, proteins and lipids, at the oil-water interface of the globules. The interfacial curvature of the globule was shown to influence crystallization. XRDT is a complex and expensive technique that cannot be used routinely in food analysis, but the thermal events that accompany the structural changes might easily be identified by DSC-XRDT.
Session 33, Applications of calorimetry in food and biological materials
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