PH—Postharvest Technology: Water Vapour Adsorption Properties of Fuzzy and Starch-coated Cottonseeds

Abstract

Adsorption isotherms of fuzzy and starch-coated cottonseeds were determined for relative humidity (r.h.) in the range between 11 and 100% each at 5, 15, 25, 35, and 45°C. Fuzzy and starch-coated cottonseeds exhibited S-shaped isotherms. The Guggenheim–Anderson–Boer (GAB) equation, regressed using direct non-linear regression method, described the sorption behaviour of the samples satisfactorily. Estimated GAB constants were in good agreement with the literature and/or what the theory of the GAB equation dictates. In the multilayer sorption region, fuzzy and starch-coated cottonseeds had almost the same equilibrium moisture contents X at the same r.h. and temperature, and X increased linearly with increasing r.h.. In the capillary condensation sorption region, values for X of the cottonseeds departed from each other and the gap became more pronounced with increasing r.h. and decreasing temperature. Starch-coated cottonseed exhibited always smaller X values than the fuzzy cottonseed in the capillary region. Monolayer moisture content X m was determined to be 4.35 and 4.59% d.b. for the fuzzy and starch-coated cottonseeds, respectively. Average heat of adsorption Q estimated using the Clasius–Clapeyron equation was 74 and 70 kJmol −1 below X m, and 47 and 46 kJ mol −1 above X m for the fuzzy and starch-coated cottonseeds, respectively.