Effect of different drying procedures on physicochemical properties and flow behavior of Aloe vera (Aloe barbadensis Miller) gel

Abstract

The main aim of this study was to evaluate the effect of different drying procedures, used at industrial scale, on physicochemical properties, such as water activity, solubility, hygroscopy and, also, on the flow behavior of Aloe vera (Aloe barbadensis Miller) gel. The drying methods applied were: spray-drying, industrial freeze-drying, refractance-window-drying and radiant-zone-drying. Further, the flow behavior of all dehydrated Aloe vera samples was investigated at different temperatures (10, 20, 30, 40, and 50 °C). In addition, fresh Aloe vera gel was lyophilized and used as a reference. All processed samples exhibited lower water activity (<0.4), higher solubility (>90%) and higher hygroscopy (>80%) than the reference sample. Moreover, a shear-thinning behavior, exhibited by the fresh Aloe vera gel, was modified to a Newtonian behavior in all the processed samples. Interestingly, the viscosity of all the processed samples exhibited a higher temperature dependence (Ea > 28 kJ/mol) than the reference sample (Ea = 21 kJ/mol). These important changes in the physico-chemical properties and, also, in the flow behavior of the dehydrated Aloe vera samples could be related to structural modifications observed for the acemannan polymer, the main bioactive polymer present in Aloe vera gel; and in particular, to the modification of its degree of acetylation.