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) and two thicknesses (4 and 6mm) slices. Some slices were blanched in water at 90 ^oC for 5 mins and some untreated. The slices were dried in the sun or oven (50 ^oC , 70 ^oC , 90 ^oC ). The bulk density, dimensional changes and moisture loss were investigated. Moisture loss and percent shrinkage increased with higher temperature and longer drying time. 4mm thick samples lost more moisture and higher % shrinkage than 6mm thick samples, although not significantly (P>0.05). Logarithmic equations gave best fit of moisture loss with time at the different temperatures. Initial sample thickness had a greater impact on shrinkage than sample 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 length (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.

Keywords: moisture content, drying kinetics, blanching, dimensional changes, bulk density.