MOISTURE ADSORPTION ISOTHERMS AND HEAT OF SORPTION OFAGARICUS BISPORUS

Abstract

ABSTRACT Moisture adsorption isotherms of Agaricus bisporus were determined at different temperatures (5, 15, 25 and 35C) using a static gravimetric method. Several saturated salt solutions were prepared to obtain different water activities in the range of 0.11–0.93. Freeze-dried A. bisporus was equilibrated with designed saturated salt solutions. For certain water activity, the equilibrium moisture contents of A. bisporus decreased with increasing temperature. Adsorption isotherms of freeze-dried A. bisporus followed type III isotherm, which is typical for polysaccharide products. Nine models were used to fit experimental data by linear regression analysis method to ascertain the best of fit. Comparisons were based on mean relative percent error (E), standard error (SE), coefficient of correlation (R2) and residual plots. Among the models tested, the Halsey model achieved the best fit. Based on Clausius–Clapeyron equation, the net isosteric adsorption heat of A. bisporus decreased from 12.12 to 0.30 kJ/mol when the moisture content increased from 8 to 50 g/100 g dry matter. PRACTICAL APPLICATIONS A. bisporus's shelf life is only 1–3 days at ambient temperature. Drying, especially freeze-drying, is one of the main preservation methods for A. bisporus. Developing moisture sorption isotherms (MSIs) for A. bisporus could provide essential information about optimizing its drying process and storage conditions. In addition, isosteric heat of sorption in dehydrated and intermediate moisture food also plays an important role in modeling of various food processing and storage. Optimization of drying process and storage conditions of dried A. bisporus could be obtained by developing its MSI.