PREDICTING THE WATER ACTIVITY OF MULTICOMPONENT SYSTEMS FROM WATER SORPTION ISOTHERMS OF INDIVIDUAL COMPONENTS

Abstract

ABSTRACT Plots of log (water activity/mole fraction water) against the square of the mole fraction solute, usually give straight lines having slopes K. Norrish (J. Food Tech 1966, 1: 251 used K derived for binary solutions in an equation for calculating water activities of multicomponent systems, but this equation gave inaccurate results when used on solutions where a deviation from linearity occurs, or when the linear portion of the plot does not go through the origin. By using both intercept and slope, and adding a correction factor that corresponds to the contribution of the intercept to the total solute interactions to Norrish's equation for multicomponent systems, an equation was derived that accurately predicted water activities of multicomponent systems. This concept of utilizing the intercept was applied to systems containing solids whose molecular weights are not well defined. Plots of log (water activity/moles water in 100g solution) against the square of the weight percent solids in the system, gave a series of straight‐line segments. Slopes and intercepts were different for each concentration range where the straight line segments lie. An equation was derived based on this equation for water activity as a function of concentration. In the derivation, moisture transfer between two components and equality of the water activities of all phases at equilibrium was considered. The derived equation predicted accurately equilibrium water activities of mixtures of two solids.