Effect of drying conditions on the quality of vacuum-microwave dried potato cubes

The influence of drying conditions on the color, starch content, sugar content, mechanical properties and microstructure of dried potatoes was studied. Statistically significant differences between the color of raw and dried materials were observed for every drying methods. It was observed that the vacuum-microwave drying technique prevents color damage during drying. Potato cubes dried in a vacuum-microwave oven had lower starch and total sugar losses than those dried under forced convection conditions. The maximum force values obtained from compression tests indicated statistical differences between samples dried in a microwave-vacuum drier and a convection drier. The averaged force and energy required to cause 3 and 5.5 mm deformation were the highest for blanched and hot-air dried (70 degrees C) potato cubes, and the lowest for vacuum-microwave dried material (24 kPa). The application of microwave energy led to different physical changes in product microstructure, compared to those observed during hot-air drying. The extent of changes was depended on the method and parameters of drying. In both cases the drying process caused deformation and disintegration of cell walls and starch granules. Experiments show that in the case of hot-air drying the intensity of structural changes depends on drying temperature. A higher temperature causes greater damage to the microstructure of potato cubes. Microwave drying at 24 kPa ensured the shortest drying time and the best overall quality of dried potato cubes, and thus was chosen as the most appropriate technique for potato drying. (c) 2006 Published by Elsevier Ltd.