Effect of Equilibrium Water Activity on the Bulk Properties of Selected Food Powders

The bulk properties of powdered coffee creamer, infant formula, salt and sucrose at different levels of water activity were characterized by mechanical methods. These included loose bulk density, compressibility, cohesion, % irrecoverable work in compression and asymptotic modulus after stress relaxation. In the crystalline powders the physical characteristics generally followed the pattern established by the moisture content with an apparent critical water activity beyond which changes became drastic. In the creamer and formula which were very cohesive even in the dry form, the changes in bulk properties were generally more gradual. The rheological tests indicated that much of the physical changes in the salt and sucrose powders could be attributed to surface moisture. In the creamer and formula the plasticity of the particles material was also a major factor that affected the bulk behavior.