Three dimensional characterization of morphology and internal structure of soft material agglomerates produced in spray fluidized bed by X-ray tomography

Food powders such as maltodextrin are often produced in agglomerate form in spray fluidized beds in order to enhance their user properties. These agglomerates mostly have complex structures and irregular shapes. The internal structure and morphology of food agglomerates have rarely been investigated at the microscopic scale. In this work, a nondestructive X-ray micro-computed tomography technique is used as an appropriate experimental method to overcome this lack of data by a thorough characterization of the three-dimensional internal structure of maltodextrin agglomerates. A sequence of image processing steps is applied to the X-ray images in order to obtain 3D views and to extract data for the morphological characterization. The internal porosity as well as the size and spatial distribution of the pores inside the agglomerates are evaluated. Open pores formed during the agglomeration process are also determined from the X-ray images. The agglomerate shape is investigated and compared by 2D and 3D image analyses. Maltodextrin primary particles with non-spherical shape have a broad size distribution, and they may deform and overlap as they go above the glass transition temperature during the agglomeration process. A comprehensive methodology is developed based on the preflooded watershed segmentation of X-ray images to distinguish the primary particles in maltodextrin agglomerates. On this basis, the radius of gyration and the fractal dimension are calculated. A low fractal dimension of 1.8 is found, which proves-that the structure of maltodextrin agglomerates is more open and fluffier than the structure of insoluble hard material agglomerates. (C) 2015 Elsevier B.V. All rights reserved.