Abstract In this paper we predict the water activity and initial freezing point of food products (meat and fish) based on their composition. The prediction is based on thermodynamics (the Clausius–Clapeyron equation, the Ross equation and an approximation of the Pitzer equation). Furthermore, we have taken the effect of bound water into account, by using a linear relation between mass fractions of bound water and the mass fractions of soluble biopolymers. Model parameters are estimated using data of meat. The validity of the model is checked against data of fish. Good agreement with experimental data are obtained in the range of a w>0.70. Furthermore, our results remove the inconclusiveness on the prediction of bound water that exists in literature.