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Interest of energy dispersive X-ray microanalysis to characterize the surface composition of milk powder particles

Murrieta-Pazos, I., Galet, L., Rolland, C., Scher, J., Gaiani, C.
Colloids and Surfaces B: Biointerfaces 2013 v.111 pp. 242-251
X-radiation, X-ray photoelectron spectroscopy, colloids, dried milk, energy, energy-dispersive X-ray analysis, lactose, milk composition, particle size, powders, whey protein, whole milk
Energy dispersive X-ray (EDX) is a technique rarely used for organic powders. Nevertheless, this technique is of great interest in the characterization of milk particle surface. In order to validate the method, the EDX technique was tested on pure milk components, on model powders composed of different ratio of lactose/whey proteins and on whole milk powders presenting or not free fat at the surface. For all these powders, satisfactory results were obtained with correct experimental atomic percentages in comparison with expected theoretical percentages. The technique was then applied to skimmed and whole milk powders sieved in 4 fractions. The surface and the core (cut particle) were analyzed by EDX and compared. A relationship between the particle size and the surface composition was observed. X-ray photoelectron spectroscopy (XPS) often used to characterize milk powder surface, however no differences were observed between surface and core composition using this method. The depth of analysis by EDX is far more significant (1μm) in comparison to that of the XPS (5nm); hence it was concluded that the analysis of cut particle by EDX was not interesting since too close to the results obtained at the surface. Finally, the technique was coupled with XPS and successful hypothesis concerning composition gradients were done.