MOISTURE SORPTION CHARACTERISTICS OF FREEZE-DRIED BLUEBERRIES

Moisture sorption isotherms of freeze dried lowbush blueberries at 4, 16, 25, 35, and 45 degrees C were determined using indirect gravimetri c method. Moisture sorption kinetics at these temperatures and 75% RH were also investigated. The isotherms followed a type III shape with a temperature inversion effect at 0.9 water activity. They were best de scribed by the GAB equation. Net isosteric heat of moisture sorption i n freeze dried blueberries, determined using the Clausius Clapeyron eq uation, varied from 5.5 to 0.25 kJ/mol as moisture content changed fro m 8 to 36% (dry basis). Moisture adsorption kinetics in freeze dried b lueberries were well described by the first order kinetics equation. T he rate constant followed the Arrhenius relationship with an activatio n energy of 38.6 kJ/mol.