Use of the Fermi Function to Describe Wheat Four Water Sorption Hysteresis: Model Parameters χ and k Based on Vrentas-Vrentas Theoretical Simulation

Water sorption and its hysteresis are widespread phenomena that are important for food processing and food quality. In the present study, water sorption and desorption isotherms of wheat flour were measured at three temperatures using a dynamic vapor sorption (DVS) instrument, and modeled according to the Vrentas-Vrentas (VV) theory. Results showed that the degree of water sorption hysteresis decreased with an increase in temperature. In addition, overlapping between desorption and sorption isotherms was observed at high water activity. Based on this, an approach was proposed to determine the critical water content at which glass transition occurs. For both water sorption and desorption, the Flory-Huggins interaction parameter χ varied with the volume fraction of water, and a modified Fermi function was proposed using the Peleg model to describe this relationship. When desorption isotherms were modeled based on the sorption parameter χ, the VV model parameter k was expressed as a function of the volume fraction of water using a Fermi-type function.