Optimization of Process Parameters for Microwave Drying of Garlic Cloves

摘要

Application of microwaves for drying garlic cloves was investigated. A laboratory microwave-con vective dryer was developed which had the provision of regulating microwave power, air temperature and air velocity. Garlic cloves of uniform size were used in the drying experiments which were carried out at air temperatures of 40,50, 60 and 70℃, air velocities of 1.0 and 2.0 m/s and microwave power levels of 10, 20, 30 and 40 W. Microwave-convective drying was accomplished till the moisture content of the garlic cloves reduced from initial moisture content of 1.85 kg water/kg solids to a safer level of 0.06 kg water/kg solids. The drying time increased as the air velocity was increased from 1.0 to 2.0 m/s at all levels of air temperatures and microwave power. The specific energy consumption involved in all drying conditions was also estimated. The quality attributes of the fresh and dehydrated garlic cloves were evaluated for colour (L, a, b values), flavour strength and vitamin C. The rehydration ratio was also determined for the dehydrated garlic cloves. A convectionally dried commercial sample of garlic cloves from a local manufacturer was obtained. The quality attributes of this sample were compared with products dried by microwave-convective drying technique. The quality of garlic cloves, dehydrated by microwave-convective drying process, was found superior to the commercial sample. The process parameters for microwave-convective drying were optimized for the garlic cloves using Tukey's multi-comparison pair-wise test. The results revealed that the microwave power of 40 W, air temperature of 70℃ and air velocity of 1.0 m/s gave good quality dehydrated garlic cloves and involved low specific energy consumption in the drying process.