Ethanol Pretreatment Before Air Drying of Beetroot: Water Sorption Isotherms, Glass Transition Temperature and Shrinkage During Drying

This study investigates the effects of ethanol pretreatment on the drying characteristics, thermodynamic properties, and shrinkage of beetroot. Ethanol pretreatment was applied under various conditions prior to air drying at 70 °C. Water sorption isotherms were determined at different temperatures and six models were evaluated for their ability to describe sorption behavior. Ethanol-treated beetroot demonstrated a lower equilibrium moisture content and a diminished capacity for water absorption in comparison to untreated samples. Thermodynamic parameters, including isosteric heat of sorption and entropy were analyzed, revealing that the sorption process is enthalpy-driven. Water functioned as a plasticizer, resulting in a reduction of the glass transition temperature (Tg), which was effectively predicted by the Gordon-Taylor model. The ethanol pretreatment led to a slight increase in Tg values, thereby enhancing structural integrity during the drying process. Shrinkage was closely linked to moisture loss and was more accurately characterized by integrating the concept of glass transition.