Physical properties and rehydration kinetics of two varieties of cowpea (Vigna unguiculata) and bambara groundnuts (Voandzeia subterranea) seeds

The water absorption kinetics of the cowpea (varieties CW and CG) and bambara seeds (varieties BB and WB) were studied following the first order, Peleg with a proposed sigmoid model. Significant intra and inter varietal variations were observed on the physical characteristics of the seeds. In general the saturation water content was higher for the cowpea varieties (1.39-1.50 g g(-1)) and lower for the bambara varieties (0.88-1.00 g g(-1)). The proposed sigmoid model was shown to significantly describe the kinetic of absorption irrespective of the variety and temperature. The effective diffusivity of the seeds were shown to vary in the order GC > WB > BB > WC and increased as the soaking temperature increased from 35 to 45 degrees C. The variation in the effective diffusivity at 25 and 35 degrees C was observed to be linearly correlated (R-2 > 0.82; p < 0.05) to the percent seed coat, suggesting its role in the process of mass exchange. In addition the effective diffusivity varied with temperature according to the Arrhenius equation and the resulting activation energy varied from 78.8 kJ mol(-1) for GC variety to 11.20 kJ mol(-1) for WB variety. (c) 2007 Elsevier Ltd. All rights reserved.