A general method for predicting the water activity of simple and multi‐component mixtures of solutes and non‐solutes

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Abstract
Caurie's (1985) equation for predicting the water activity (aW) of binary solutions has been revised by replacing molal concentration units and activity coefficient with equivalent expressions for weight concentration (g/kg H2O). Results obtained using the revised equation, which now applies to both solutes and non‐solutes, agree closely with measured literature values. The equation reveals that the relationship between the weight concentration of solute/non‐solute binary solution or dispersion and the corresponding aW exhibits a minimum for carbohydrates and proteins. Electrolytes exhibit no such minimum and are the most effective in depressing aW while proteins are the least effective. The substitution of the new binary equation into the Ross (1975) equation results in an equation for a mixture identical with the recently corrected Ross one (Caurie, 1985), except that the correction factor in the new equation is expressed in g/kg H2O making it applicable to simple and multi‐component mixtures of both solutes and non‐solutes. The new equation has been applied to literature data from various sources and has been found to agree very closely with measured values.