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

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 (1 µm) in comparison to that of the XPS (5 nm); 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.

Advances in food powder agglomeration engineering.

Food powders are used in everyday life in many ways and offer technological solutions to the problem of food production. The natural origin of food powders, diversity in their chemical composition, variability of the raw materials, heterogeneity of the native structures, and physicochemical reactivity under hydrothermal stresses contribute to the complexity in their behavior. Food powder agglomeration has recently been considered according to a multiscale approach, which is followed in the chapter layout: (i) at the particle scale, by a presentation of particle properties and surface reactivity in connection with the agglomeration mechanisms, (ii) at the mechanisms scale, by describing the structuration dynamics of agglomerates, (iii) at the process scale, by a presentation of agglomeration technologies and sensors and by studying the stress transmission mode in the powder bed, and finally (iv) by an integration of the acquired knowledge, thanks to a dimensional analysis carried out at each scale.

Comparative study of particle structure evolution during water sorption: skim and whole milk powders.

Surface composition of dairy powders influences significantly a quantity of functional properties such as rehydration, caking, agglomeration. Nevertheless, the kinetic of water uptake by the powders was never directly related to the structure and the composition of the surface. In this work, the effect of relative humidity on the structural reorganization of two types of dairy powder was studied. The water-powder interaction for industrial whole milk powder, and skim milk powder was studied using dynamic vapor sorption. The water sorption isotherms were fitted with a Brunner-Emmet-Teller model and each stage of the sorption curve was analyzed with a Fickian diffusion. The water content in the monolayer predicted for each powder and the moisture diffusivity calculated were discussed and compared. Concurrently, powders microstructure and powders surface under variable relative humidity were assessed by X-ray photoelectron spectroscopy, scanning electron microscopy coupled with energy dispersive X-ray and atomic force microscopy. A correlation between the data obtained from the sorption isotherms and the modifications of structure allowed us to conclude that powder microstructure and chemical state of the components could play an important role in determining the water diffusivity.