Drying kinetics and quality of vacuum-microwave dehydrated garlic cloves and slices

Whole garlic cloves, halved and sliced were subjected to vacuum-microwave (VM) drying at three microwave power levels: 240, 480 and 720 W. The process of drying was described by a sigmoid function. Slicing the cloves prolonged the time of drying. An increase in microwave power resulted in increased drying rate. The temperature of garlic samples measured in a vacuum flask amounted to 50 degrees C till the moisture content of 0.6 g/g dry matter. Further drying of garlic was associated with temperature increase to about 70 C. Decreasing moisture content, till 0.6 g/g dry matter, was accompanied by decreasing relative volume of the dried material. On exceeding this value no further change in volume of the slices was observed, though for whole cloves and halves a marked increase in volume was observed. Lowering of moisture content below 0.6 g/g dry matter and increasing microwave power caused an increase in garlic cloves compressive strength. Increasing the degree of the material subdivision and microwave power resulted in increased water absorption capacity. Drying the garlic samples with the VM made the color brighter, shifting it towards red and blue, compared to fresh garlic cloves. The best retention of volatile oils was observed for garlic slices dehydrated with microwaves at 720 W. (C) 2009 Elsevier Ltd. All rights reserved.