Theoretical Background Water Vapor Sorption Isotherms

The term sorption is generally used to describe the initial penetration and the dispersal of the permeant molecules into food matrices (Chirife and Iglesias 1978) and, more generally, into all kinds of polymers (Naylor 1989; Tsujita 1992). This term includes adsorption, absorption into microvoids, and cluster formation. When a food matrix is placed in a humid atmosphere, the relationship between the ambient water activity aw ð Þ and the water concentration Qw ð Þ in the material at a given temperature is described by an equilibrium sorption isotherm Qw 1⁄4 f aw ð Þ ð Þ. Water concentration Qw ð Þ can be defined as the ratio of the mass of sorbed water at equilibrium Mw ð Þ to the mass of dry matter Md ð Þ: