Drying of carbohydrate food in superheated steam and hot air - Characteristics of coloring of potato slice surfaces

Abstract

Drying by use of atmospheric superheated steam (SHS) as a drying medium has various characteristics: the materials to be dried are heated rapidly by steam condensation, they are sterilized and their oxidization at high temperature is reduced in comparison with that when air is used. Therefore this drying method is petentially applicable to food processing. In this study, coloring of raw sliced potatoes during SHS drying and hot air drying at 170°C and 240°C under atmospheric pressure was investigated. The results showed that starch granules remained at the surface of the samples dried with hot air, but no starch granules remained after the SHS drying. The potato slices dried with SHS were found to be darker in color and to have a glossier surface. Starch gelatinization proceeded more rapidly in SHS drying, than in hot air drying, and amounts of low molecular weight carbohydrates and free amino acids produced, which are thought to contribute to coloring, were higher in SHS drying than in hot air drying.