Moisture adsorption isotherms and thermodynamics properties of sucuk (Turkish dry-fermented sausage)

Moisture adsorption isotherms of sucuk were determined using the isopiestic method at 10 °C, 20 °C and 30 °C and within the range of 0.2–0.9 water activity. The isotherms of sucuk exhibited Type II behavior according to BET classification. The adsorption data were analyzed using mathematical equations of Halsey, Caurie, Peleg, Smith, Oswin, Henderson, Modified-BET, GAB, Ferro-Fontan and Harkins–Jura. The best fit of experimental data was obtained with Peleg equation in the range of temperatures and water activities investigated. Thermodynamic properties such as differential enthalpy and entropy, enthalpy–entropy compensation, spreading pressure, net integral enthalpy and entropy were determined from moisture adsorption isotherm data of sucuk. The net isosteric heat of sorption and differential entropy decreased with increasing moisture contents in an exponential function. The spreading pressure increased with increasing water activity, and decreased with increasing temperature. The net integral enthalpy decreased with increased moisture content. The integral entropy increased with moisture content, but it was negative in value. The enthalpy–entropy compensation theory was applied to water adsorption of sucuk.

Research highlights
► Adsorption isotherms of sucuk are investigated.
► The adsorption data are analyzed using mathematical equations.
► Thermodynamic properties are determined from moisture adsorption isotherm data of sucuk.
► The enthalpy–entropy compensation theory is applied to water adsorption of sucuk.