Microwave Dielectric Heating for Spray Drying of Mandarin Orange Juice

Abstract

The application of microwave dielectric heating to spray drying of mandarin orange juice was investigated by mobile miner type spray dryer of Niro Atomizer Company connected with a microwave generator with the frequency of 2450 MHz. The improvement of the yield of dryed powder was demonstrated by microwave heating. In drying of mandarin orange juice, sticking on the wall of dryer was observed by melting of dryed powder at higher drying temperature. On the contrary, adhesion on the wall resulted by insufficient drying was observed at lower drying temperature. It was concluded that the optimal drying conditions were critically in a narrow range, and that in this particular study, the optimal outlet temperature of hot air was determined to be around 55°C for mandarin orange juce and 70°C for the juice added with 3% of dextrin. Drying rate of mandarin orange juice rapidly decreased at less than 100% moisture content (dry basis), and microwave absorption efficiency for orange juice compared with that for pure water decreased also rapidly at 70-80% moisture content (dry basis). From this facts, it was suggested that concentrated quick microwave heating at about 100% moisture content should be effective for increasing the yield of dryed powder.