Water sorption properties of dutch type semi-hard cheese edge in the range of common storing temperatures

Moisture sorption isotherms of Dutch type semi-hard cheese edge in the temperature range of 10- 25 °C and water activity (Aw) from 0.11 to 0.98 were determined using manometric method. The sorption curves had a sigmoid shape. The equilibrium moisture content (EMC) of cheese samples increased with an increase in Aw at a constant temperature both for water adsorption and desorption. An increase in temperature caused an increase in Aw for the same moisture content (MC) and,if Aw was kept constant,an increase in temperature caused a decrease in the amount of absorbed water. Critical values of equilibrium moisture content,corresponding to the Aw = 0.6,were between 11 % MC (w.b.) and 17% MC (w.b.) both for moisture adsorption and desorption. Values of sorption heat were calculated from moisture sorption isotherms by applying the Clausius-Clapeyron equation. Values of the heat of desorption are higher than those of adsorption and the difference increases with the MC decrease. Heat of sorption decreased from 48.5 kj/mol (∼5.5 % MC w.b.) to the values approaching the heat of vaporization of pure water,free MC. The critical value for free water evaporation is about w = 27% (w.b.) for the range of temperature 10-25 °C.