A COMPARATIVE-STUDY OF THE EFFECTS OF WATER-CONTENT ON THE COMPACTIONBEHAVIOR OF SOME FOOD MATERIALS

This study compares compaction and stress transmission data for crysta lline and amorphous food powders of different water content compacted in a cylindrical geometry. An increase in water content leads to a gre ater density for a given pressure, with sucrose and potato starch appr oaching zero porosity at the higher water contents. The limiting gradi ent of the Heckel plot, which is a generalised deformation stress, dec reases with increasing water content for all the materials studied. In potato starch and maltodextrin this is believed to be due to a plasti cisation mechanism; whereas in sucrose and sodium chloride water lubri cates the particle movement. The latter is supported by an increase in the ratio of transmitted to applied stresses with water content for s ucrose and sodium chloride, which is consistent with a reduction in wa ll friction. The stress ratio is largely independent of compacted heig ht as predicted by the classical semi-particulate analysis for the suc rose and sodium chloride. By contrast the stress ratio shows irregular variation with water content and degree of compaction for potato star ch and maltodextrin.