Water Activity Determination with the Proximity Equilibration Cell

Abstract

ABSTRACT The objective was to develop a new method for water activity (a w ) determination. A reference material (circle of filter paper) of known sorption isotherm was equilibrated to the sample. Sorption isotherm data for this paper were obtained by equilibrating for 24 hr to each of six salt slushes; these data were described well by a linear equation relating moisture content to log (1 − a w ). This equation served as the calibration curve. Results showed that this new method (1) does not require a vacuum, (2) gives a linear calibration equation, (3) is applicable over the a w range from 0.40–0.98, and (4) with minor replication can bring the standard deviation of the mean to less than ± 0.01.