Effect of Temperature on the Moisture Sorption Isotherms and Water Activity Shift of Two Dehydrated Foods

The water activity (a_w) of eight salt solutions was determined at three temperatures (25, 30, 45°C) using a pressure transducer‐vapor pressure manometer. The a_ws of the salts showed a decrease with increasing temperature, which was explained with the help of a thermodynamic equation. This is opposite to the increase in a_w with increase in temperature for foods. Moisture sorption data for fish flour and cornmeal were obtained at 25–65°C. The Guggenheim‐Anderson‐deBoer model was evaluated and shown to be comparable to the Brunauer‐Emmett‐Teller model for prediction of the monolayer. Product was equilibrated at different a_ws at 25°C then subsequently shifted to 30°C and 45°C in a sealed chamber. The resultant a, change, measured on the Kaymont‐Rotronics, was predictable from the isotherm at each temperature using the Clausius Clapeyron relationship.