Moisture Adsorption Characteristics of Bambara Groundnut (Vigna subterranea) Powders

Adsorption equilibrium moisture content data of Bambara groundnut (Vigna subterranea) powders were determined at 20, 30 and 40 ° C using the static gravimetric method. The equilibrium moisture content of the powders decreased with increasing storage temperature and increased with water activity. Four commonly used three-parameter moisture sorption isotherm models were evaluated for their ability to fit the experimental data using direct non-linear least squares regression techniques. The models were the modified Henderson, modified Chung-Pfost, modified Oswin and the modified Halsey models. The models were compared for their goodness of fit using their percent root mean square of error (%RMS) and standard error of estimate (SEE). The modified Chung-Pfost moisture sorption isotherm model gave the best fit to the experimental data (RMS = 8.321 % and SEE = 0.051) The net isosteric heats of sorption of dehulled bambara groundnut powders (DBP) were generally higher than those of the undehulled (UBP) seeds and decreased with increase in moisture content. Similarly, the isosteric heat of adsorption of the first molecule of water (Qo) was higher in the DBP than in the UBP. Conversely, the characteristics moisture content (Mo) of the DBP was lower than that of the UBP. The entropy of sorption of DBP was higher (-0.050 to-0.030 kJ K-1 mol-1) than that of UBP (-0.055 to-0.039 kJ K-1 mol-1) showing a greater degree of freedom of moisture in powders of dehulled than those of undehulled bambara groundnut