Simultaneous Drying and Modification of Properties of Starch Using Vacuum Microwave Treatment

Abstract

The prospect of modifying starch properties while drying was investigated. Potato starch (18% moisture, dry basis) was vacuum microwave treated for different durations (60 to 600 s) with power ratings of 600, 1,000, and 1,500 W at a reduced pressure of 5,000 Pa (absolute). The drying rate was observed to be partially constant but was accompanied by a curious rise in sample temperature. Under a polarized light microscope, reduction in granule size was noticed, which was confirmed from the bulk density measurements, and this shrinkage may be explained by the loss of constituent water. Water absorption capacity of the treated starch samples was further studied at 55°C. The results showed a sudden increase in the capacity, indicating a reduction in gelatinization temperature of starch. This may be attributed to the change in nature of starch from crystalline to amorphous as shown by X-ray diffractograms and to the cracks developed on the granule surface during treatment seen in the scanning electron microscope images. This modified starch can serve well in the paper and food industry.

Keywords:

• Microwave drying
• Starch
• Vacuum drying

ACKNOWLEDGMENTS

The authors thank Dr. Christa Blank for the polarized light microscope images and Kathrin Mende for her administrative support.