Drying of sliced raw potatoes in superheated steam and hot air

Drying experiments were conducted on raw potato slices, using atmospheric pressure superheated steam and hot air as drying media at 170 and 240 degreesC. Mass changes of the material were continuously measured, the conditions of cross section near the surfaces were observed with an electron microscope, also color changes of their surface were measured during drying. The respective drying methods and temperature conditions were compared and it was found that, in the case of superheated steam drying, moisture content temporarily increases due to steam condensation in the initial stage of drying, therewith, as well as starch gelatinization rapidly develops. Meanwhile, in case of hot air drying, starch gelatinization occurs more slowly than with superheated steam drying and that non-gelatinized starch granules remain on the surface when drying was completed. Furthermore, surface color measurements showed that samples dried by superheated steam were more reddish than ones dried by hot air and the surfaces were more glossy, because no starch granules remain on the surface in case of superheated steam drying.