Effects of Drying Conditions on Water Sorption and Phase Transitions of Freeze-Dried Horseradish Roots

The water sorption isotherms for freeze-dried horseradish roots (Armoracia rusticana) were determined using the interval sorption technique, and the thermal behavior of dried and rehumidified products was analyzed using differential scanning calorimetry. The hygroscopicity of the dried material increased when the surface temperature during freeze-drying was increased from 20°C to 60°C. Both sorption and thermal data showed that drying at high surface temperatures affected the physical structure of the material, resulting in increased water adsorption, decreased glass transition temperature, and increased unfreezeable water content. Water sorption isotherms and thermal data can be used to determine the proper drying and storage conditions for horseradish roots.