Design of U-column microwave-assisted extraction system and its application to pigment extraction from food

A microwave-assisted extraction (MAE) system for biological material was designed with a cylindrical cavity, a rectangular wave guide, a magnetron of 2450 MHz and a U-column made of two glass columns; one for heating solvent and the other for the packed bed. The central focusing, dipolar power mode in the cavity was simulated, and the actual mode when using the extraction column was verified with dummy food (agar containing 0-5% NaCl). The position and the alignment of the U-column in the cavity were examined using two design strategies. Firstly, the heating column was matched to the central focusing mode to achieve the highest heating rate of the solvent, and secondly, the packed column was positioned at a mild power mode to disrupt biological cells to increase the extraction rate. The set-up of the MAE system was applied successfully to the extraction of the edible yellow pigment from Cape Jasmine (Gardenia Jasminoides Ellis) and the extraction yield was 50% higher than the conventional extraction method on the basis of identical thermal energy input and flow rate. The extract from the MAE system showed a pulsating flow pattern with a nearly constant volume fraction. In spite of focused microwave irradiation to the heating column, the temperature of the extract was self-regulated in the range of 70-95 degrees C.