Moisture Adsorption Isotherms and Thermodynamic Properties of Auricularia auricula

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Abstract

Moisture adsorption isotherms of Auricularia auricula were determined using the gravimetric static method at 15–35C and within the range of 0.1–0.9 water activity. The adsorption data were fitted into eight isotherm models. The best fit of experimental data was obtained with GAB model in the range of temperatures and water activities investigated. The moisture adsorption isotherms obtained were type II sigmoid shape. The thermodynamic properties such as net isosteric heat, differential entropy and spreading pressure were also determined from moisture adsorption isotherm data of A. auricula. The net isosteric heat of adsorption and differential entropy decreased with increasing moisture contents. From the values obtained for net isosteric heat and differential entropy, it was verified that the enthalpy–entropy compensation theory could be applied, the process being carried out by enthalpy (Tᵦ > Tₕₘ). The spreading pressure increased with increasing water activity, and decreased with increasing temperature.

PRACTICAL APPLICATIONS: Auricularia auricula, belonging to heterobasidiae of basidiomycetes and also called Jew's ear, wood ear, red ear, black tree fungus or ear fungus, is a nontoxic edible mushroom widely used in traditional Chinese cuisine and is known for their pharmaceutical effects in Chinese herbal medicine. Increasing attention has been paid to its exploitation and utilization in food industry. The objective of this study was to investigate the adsorption isotherms of A. auricula at 15C, 25C and 35C to select the most suitable model describing the isotherms, to determine the thermodynamic properties and to evaluate the application of the enthalpy–entropy compensation theory.