Searching the most optimal model of water sorption on foodstuffs in the whole range of relative humidity

Water sorption on foodstuffs is very important in different areas of food science engineering. However, usually measured range of relative humidity covers only two of three stages of water sorption mechanism i.e. polymolecular sorption and capillary condensation. Since in this range different water sorption models can fit the experimental data well it is hard to decide which model is the most correct. In this study the results of water sorption isotherms measured from low humidity levels on marjoram, dill, granulated garlic, semolina, skim milk powder and ground coffee are reported. They are fitted by the most popular models applied in food science (i.e. proposed by: Halsey, Lewicki, Henderson, Chung and Pfost, Ferro Fontan et al. and Guggenheim, Anderson and de Boer (GAB)). We also extend the study to the newest models successfully applied in food engineering, i.e. the generalized D’Arcy and Watt model (GDW) and the approach of the cooperative multimolecular sorption (CMMS). Finally, we discuss the limits of the models at low humidity levels, the possibility of reduction to Henry’s law and we show the advantages and disadvantages of all approaches. It is concluded that among studied models the GDW equation seems to be the best for description of data in the whole range of relative humidity.