Sorption isotherms of barnyard millet grain and kernel

Abstract

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