Résumé
Agglomeration technologies are considered as a relevant way to improve functionalities of food powders. The agglomeration process makes it possible to limit segregation phenomena, to reduce dust production, to improve wettability and powders hydration during use, etc. Although largely used in the field of dairy or cereal food products, agglomeration processes are still managed with more or less empirical approaches, and tools. The objective of the present study is to investigate the agglomeration technologies according to a generic approach by considering similar external strengths (water addition, heat treatments and mechanical energy input) applied at different levels and for different times, on the final powder properties. Experiments were realized using one food powder as raw material (i.e. durum wheat semolina) and three different technologies that have been considered for food powder agglomeration (i.e. spray dryer, fluidized bed, and low shear mechanical mixer coupled with a air dryer). Different process conditions of temperature, residence time, and water addition level were tested at pilot scale. Agglomeration yield to produce grains within a specific size range (between 1 and 2 mm diameter) was measured in order to evaluate the process efficiency. To compare the product quality, the agglomerates were characterized according to different parameters related to physical properties (size distribution, morphology, porosity, density, microstructure, friction coefficient), biochemical modifications (extend of starch gelatinization), and functionalities (rehydration and water absorption). The results firstly demonstrated that it is possible to agglomerate food powder using very different technologies. The agglomeration yields were significantly affected by the process type and also by the process parameters. Characterization of the obtained agglomerates demonstrates significant differences in term of internal structure and intensity of the physicochemical changes induced by the process. The results are discussed with regards to the thermal treatment intensity as a function of the real product water content during processing. The paper tries to develop some generic criteria to describe the agglomeration mechanisms for food powders and to propose some agglomeration scenarios.