The influence of drying on the physical properties of sweet potato slices

Abstract

The effects of varying drying conditions on the physical properties of sweet potato slices were studied. Fresh tubers were peeled, washed and cut into two shapes (rectangular: 50 x 60 mm and cylindrical 60 mm diameter) of two thicknesses (4 and 6 mm) slices. Some slices were blanched in water at 90oC for 5 mins and some unblanched. Both were either sun dried or oven dried at various temperatures; 50 oC , 70 oC and 90 oC. The bulk density, dimensional changes and moisture loss were investigated. The results shown that, moisture loss and percent shrinkage increased with increased in temperature. Sweet potato of 4 mm thick samples lost more moisture with higher % shrinkage than 6 mm thick samples, although not significantly (P>0.05). Logarithmic equations gave best fit of moisture loss with time at the different temperatures. Generally, in all the samples, thickness had a greater influence on % shrinkage than shape. Blanching minimized %shrinkage although not significantly (P>0.05). Greater shrinkage took place in the sample thickness (up to 63%) than across product diameter or thickness (values up to 26.3%). % shrinkage can be predicted using either the linear or logarithmic equations. The bulk densities of dried sweet potato slices were not influenced by blanching.