Various postharvesting processes such as handling, drying, storing and transportation of pistachio nuts are affected by their equilibrium moisture content (EMC). The static gravimetric method, along with different saturated salt solutions, was used in a range of water activity of 0.11-0.88, and at 15, 25, 35 and 40C to obtain sorption isotherms of pistachio nuts. Each set of sorption data was fitted to six mathematical equations, including Brunauer, Emmett and Teller; Guggenheim, Anderson and De Boer; Smith; Oswin; Halsey; and Henderson. The Smith model gave the most appropriate results (fitness) over the entire range of the mentioned temperatures. The isosteric sorption heats were determined for adsorption and desorption of pistachio nuts using the relevant thermodynamic relations (i.e., Clausius-Clapeyron equation). Based on experimental sorption data, a noticeable hysteresis effect between adsorption and desorption processes was observed, and their EMC plots were significantly deviated and different from each other.
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