An Isothermal Sorption Model Based on the Flory-Huggins Theory: Application to Analyze Water Sorption of Wheat Flour

In this work, an isothermal sorption model was proposed based on the Flory-Huggins theory. In the framework of the proposed model, adsorption of the bound water was assumed to follow the Langmuir isotherm, and the adsorption of the rest water to the solid-bound water mixture was described using the Flory-Huggins adsorption theory. In addition, the contribution of elasticity effect to chemical potential of water was also included into the model and calculated based the phantom model of rubber elasticity theory. Water adsorption and desorption isotherms of wheat flour were determined using a dynamic vapor sorption system at 20, 30 and 40 ℃, and adopted to validate the proposed model. The results showed that the proposed model could give a good prediction of isothermal water sorption in wheat flour, with the Flory-Huggins interaction parameter χ ranging from 0.86 to 1.52 and the cross-linking density of polymer ranging from 3000 to 6400 mol/m³, which suggested that the model was reasonable. Analyzing the water sorption of wheat flour based on the proposed model indicated that the impact of temperature on equilibrium water content could mainly attribute to its influence on the Langmuir water, in addition, mixing effect dominated the chemical potential of water at low-mediate water activities, while elasticity effect became nonnegligible at high water activity levels.