Reconstitution of fruit powders: A process – structure – function approach

Abstract

Reconstitution of six fruit powders, compacted and non-compacted, were studied. It appears that powder reconstitution behavior under sheared conditions was significantly different with regards to the water activity (aw). At low aw, the powders exhibit a glassy state with a stiff surface measured by Atomic Force Microscopy and porous/angular shapes were observed by Scanning Electron Microscopy. In that case, increasing the shear rate accelerated the kinetics of reconstitution by improving water penetration through particle surface pores thus reducing the reconstitution time. Therefore, the reconstitution is shear rate dependent. At high aw, the powders are under a rubbery state with a soft surface and a smooth shape. Under these environmental conditions (i.e. above powder's glass transition temperature), increasing the shear rate did not improve their reconstitution. Therefore, the reconstitution kinetics is not shear-dependent in the stirring rate studied (from 800 to 1500 rpm). It is suggested that the viscous layer created on the particle surface blocks the entrance of water for these powders rich in sugar and presenting low glass transition temperatures.