Raoult's law based food water sorption isotherm

A new model of water sorption isotherm is developed on the basis of Raoult' s law. It is assumed that water present in food occurs in two states, as fr ee water with properties of the bulk water and as water of hydration. Hydra ted molecules are considered as new entities with molecular weights larger than those of non-hydrated molecules. Hydration reduces the free concentrat ion of water and thus affects water activity in solution. Application of the developed equation to food sorption data showed that it gives approximation of sorption isotherms much better than that offered by the GAB model. Moreover, it predicts infinite adsorption at a(w) = 1, the p roperty which is not offered by the GAB equation. The new equation makes it possible to interpolate isotherms at high water activities close to one. T he probability that the new equation will fit the food isotherm with small RMS is higher than 90% and substantially exceeds that found for the GAB mod el. As a two-parameter model it makes substantial improvement over the thre e-parameter GAB equation. (C) 2000 Elsevier Science Ltd. All rights reserve d.