Moisture adsorption behaviour of oatmeal biscuit and oat flakes

Adsorption isotherms of oatmeal biscuit (convective-baked and microwave-baked) and oat flakes were determined using a gravimetric static method at 5, 20, 40 and 60 °C (relative humidity range 0.03–0.96). The oatmeal biscuits and oat flakes exhibited Type III and II behaviour, respectively, with the sorption capacity decreasing with increasing temperature. The Ferro-Fontan model provided the best description of the experimental sorption behaviour, followed by the Guggenheim–Anderson de Boer equation. Differential enthalpy showed a power law relation with moisture content, with differential entropy also decreasing with increasing moisture content. The linear relation between differential enthalpy and entropy confirmed the existence of compensation. Spreading pressure increased with increasing water activity and decreasing temperature. Net integral enthalpy decreased with increasing moisture content. However, net integral entropy increased with moisture content, but was negative with respect to the entropy of water.