BEHAVIOUR OF SWEET POTATO MOISTURE CONTENT IN A HYBRID DRYING SYSTEM

The aim of this study is to investigate different time-dependent drying and moisture content under different infrared (IR) and hot-air drying levels and product quality. In this experiment it was used a hybrid drying system to minimize energy consumption during the drying operation and to reduce environmental impact by reducing product loss in wastes. Three different levels of sweet potato slices thickness (1, 3, 5 mm), were pre-treated by dipping into a solution of 0.5 % sodium meta-bisulphite and 1% citric acid for 30 min. Four different levels of infrared radiation (0.861, 0.973, 1.039 and 1.161 kW.m-2) and three different levels of air-drying temperature (45, 55 and 65 degrees C) were using. The changes in moisture content during the drying process with a constant air velocity of 1.2 m. s-1 were noticed. The moisture content decreased with drying time. To obtain the desired moisture content from (6.92% to 7.52%), the drying time for 1mm and 0.861 kW.m-2 was 165,150 and 105 min while for 5mm and 1.161 kW.m-2 was 330, 270 and 240 min at 45, 55 and 65 degrees C, respectively. The total energy consumption decreased from 14.685 kW. h to 5.72 kW. h as the radiation intensity increased from (0.861 to 1.161 kW.m-2).