Sorption Isotherms of Barnyard Millet Grain and Kernel

The moisture sorption isotherms of grain and kernel of barnyard millet (Echinochloa frumentacea) were determined at 20, 30, 40, and 50 °C. A gravimetric static method was used under 0.112–0.964 water activity (a _w) range for the determination of sorption isotherms. The models were compared using the coefficient of determination (r ²), reduced chi-square (χ ²) values, and on the basis of residual plots. In grain, modified Chung–Pfost (r ² > 0.99; χ ² < 0.7) and modified Oswin (r ² > 0.99; χ ² < 0.55) models were found suitable for predicting the M _e –a _w relationship for adsorption and desorption, respectively. Modified Henderson model was found to give the best fit (r ² > 0.99 and χ ² < 0.55) for describing the adsorption and desorption of the kernel. The isosteric heat, calculated using Clausius–Clapeyron equation, was varied between 46.76 and 61.71 kJ g⁻¹ mol⁻¹ at moisture levels 7–21% (d.b.) for grain and 47.11–63.52 kJ g⁻¹ mol⁻¹ at moisture level between 4% and 20% (d.b.) for kernel. The monolayer moisture content values ranged from 4.3% to 6% d.b. in the case of adsorption of barnyard millet grain and 5.2–6.6% d.b. in the case of desorption at the temperature ranges of 50–20 °C. The monolayer moisture values of barnyard millet kernel ranged from 4.4% to 6.67% d.b. in adsorption and 4.6% to 7.3% d.b. in desorption in the temperature ranges of 50–20 °C.