Density Changes in Selected Agglomerated Food Powders Due to High Hydrostatic Pressure

Traditional compression tests are usually carried out by using the Brazilian test, confined uniaxial compression cells, and cubical triaxial tester. The high hydrostatic pressure unit (HHP) may be added as a new and useful tester to the compression test family because of its unique high pressure range and multi-directional forces. The bulk density changes of selected food agglomerates affected by hydrostatic pressure, HHP processing time, agglomerate size, and water activity after compressed by HHP were studied and assessed by a modified Hausner ratio. The microstructures of these agglomerates before and after HHP treatment were observed by SEM. It was found that the higher the pressure, the higher the bulk density for each material. Beyond a certain high pressure, the bulk density remained constant and the SEM observations showed there was little void space within the compressed samples for each material, therefore, the HHP unit could be used to measure the `ultimate bulk densityʹ for agglomerated powders. The HHP processing time had no effect on the final bulk density at a constant pressure. The compressed bulk densities at the same pressure for powders with different initial particle sizes and water activities were not significantly different. The modified Hausner ratio was higher for larger agglomerate under the same pressure.