Influence of water activity on the compressibility and mechanical properties of cocoa products

The work described in this paper investigated influence of content (cocoa, crystal and sugar powders, milk powder and maltodextrin) and water activity (at three levels of 0, 0.34 and 0.65) on compressibility and mechanical properties of cocoa products. The flow characteristics of powders were determined according to the Jenike test. Compression test was done by ZWICK 1445 at the compressive stress of 5.34 kPa. Ingredients of cocoa powder beverages are characterized by very diverse particle size distribution and bulk density which in turn has an influence on relative humidity of powders. An increase of water activity in powders causes an increase in cohesion for all powders. Particle size has an influence on the values of cohesive forces and compressibility ratio. The increase of water activity in powders causes the increase of flow index. The increase of normal consolidating stress for cocoa causes the increase of flow index. Crystal sugar has the greatest values of flow index at all the levels of water activity.