Drying of aqueous green tea extracts using a supercritical fluid spray process
Author: D. Meterc and M. Petermann and E. Weidner
Natural extracts are widely used in groceries, in pharmaceutics and nutraceuticals. For foods these extracts are mainly used for flavoring or coloring the products. For pharmaceuticals and nutraceuticals active ingredients like antioxidants are of special interest. Traditionally these extracts are obtained by water or organic solvent extraction. Afterwards the liquid extracts are dried with classical spray drying techniques or freeze drying. In this work a new process for the gentle drying of natural extracts is presented. The process is based on a high-pressure spray technique called particles from gas saturated solutions (PGSS). The solution to be dried is dosed with a high-pressure pump to a static mixer, where compressed and preheated carbon dioxide is added. Afterwards this mixture is rapidly depressurized from high pressure via a nozzle into a spray tower, operated at ambient pressure—fine droplets are formed. By adjusting the pre-expansion conditions it is possible to evaporate the solvent in spray tower. The solvent can be withdrawn with the expanded carbon dioxide and finally a dry powder of the extract is obtained. Like the most supercritical fluid processes the drying is carried out at low temperature (30–60 °C) and in an inert, oxygen-free atmosphere. This makes the process very promising for sensitive substances. First investigations with this technique were made with green tea extracts, which contain antioxidants polyphenols. Dry and free flowing powders were obtained by the spray process without degradation of the active ingredients.