Abstract
The moisture sorption isotherms of corn powder prepared from corn kernels roasted for 20 min at 160, 180, 200, 220, and 240°C were determined at 20°C using the static gravimetric method over the range of water activities (aw) of 0.11~0.90. The moisture sorption isotherms showed a typical sigmoid shape, and the equilibrium moisture content tended to increase with increasing aw, and increased sharply at above 0.75 aw. At above 0.53 aw, the equilibrium moisture content of the roasted corn powder increased with the increase in the roasting temperature. Six mathematical models (Bradley, Caurie, Halsey, Henderson, Kuhn, and Oswin) were used to fit the experimental data. The Oswin, Caurie, Henderson, and Halsey models were found to have suitability for describing the sorption curves, and the Oswin model was the best fit model for all the roasting temperatures. Concerning the monolayer moisture content, the Guggenheim-Anderson-Boer (GAB) equation showed high significance. The monolayer moisture content increased as the roasting temperature was increased, to 0.043 and 0.053 kg H2O/kg solids in the corn powder roasted at 180°C and 240°C, respectively. These results suggest that the roasting temperatures of the corn kernels affected the moisture sorption characteristics (20°C) of the corn powder.
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