Empirical Models for Moisture Sorption Isotherms at Very High Water Activities

Abstract
Published moisture sorption data of selected gums, fibers and starch determined at water activities of up to 0.98‐0.99 were fitted by an empirical three parameter model. It had the general mathematical structure of the GAB model but its abscissa's range was expanded from zero to one, to zero to infinity. This was done by substituting In [1/(1 ‐aw)] or aw/(1‐aw) for aw, terms that could be derived from Henderson's and Oswin's models. This hybrid model with either substitution had a particularly good fit to the isotherms part that accounted for moisture sorption at high water activities. The model with the logarithmic transformation, however, appeared to be more practical and to better account for the intermediate part of the moisture sorption isotherm.

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