Evaluation of the drying process in spouted bed and spout fluidized bed of xanthan gum: focus on product quality

It has been shown that spouted bed (SB) dryers are an alternative way to obtain high quality dried powder products. Xanthan is a biopolymer, which gives highly elastic dispersions, while at the same time exhibiting great pseudoplasticity. This hydrocolloid is widely used as a stabilizer: thickener or as gelling agent when associated to other gums. In this work, the drying of xanthan gum in two-dimensional SE, and in a two-dimensional spouted bed with additional aeration (SFB) was evaluated. The product quality was studied as a function of the gum dispersability, and of the rheological properties under steady and dynamic shear. The dried gum dispersed in water shows a similar rheological behavior to the dispersion of commercial xanthan, i.e., significant break-up of the gum structure does not occur even if the biopolymer has undergone shear drying conditions. Turbidimetric measurements were done in order to quantify the dispersability of powder materials. A light microscopic analysis has shown that the material obtained via SFB acquires a shape of large agglomerates with spins, while the commercial powder exhibits an ellipsoid shape. The SE drying process yields a material with an intermediate shape. Such results were associated to the dispersability with the powdered gum. (C) 2000 Elsevier Science S.A. All rights reserved.