Determining the Cellular Structure of Two Cereal Food Foams by X-ray Micro-Tomography

The cellular structure of two products, an extruded breakfast cereal and a short dough biscuit, was characterized by two different X-ray micro computed tomographic systems. Acquisitions were made by a compact desktop system Skyscan 1174 (Bruker mu CT, Belgium) and at the European Synchrotron Radiation Facility (ESRF, beamline ID19, France) at different resolutions (voxel size of 6.5 mu m, 7.5 mu m, 16.2 mu m and 25.8 mu m). 3D images were processed for the density, the connectivity index and the granulometry of cells and cell walls. These experiments underlined the importance of the resolution for determination of quantitative measurements such as densities and thicknesses. The median width calculated for the cell walls distribution in the biscuit dropped from 141 to 50 mu m when the voxel size changed from 25.8 to 7.5 mu m. Images well showed that even though the food products had close values of porosity 0.6 and 0.7 for biscuit and extruded breakfast cereal respectively, their cellular structures were very different. The biscuit had small cells (median value of the distribution varied from 125 to 152 mu m, according to resolution) and larger cell walls (50-141 mu m) than the extrudate (32-109 mu m) which, on the contrary, exhibited very large cells (307-400 mu m). Beyond methodological issues, these differences could be clearly attributed to the differences of compositions and processes.