Effect of soaking temperature on water absorption characteristics of selected Ghanaian cowpea varieties

Abstract

The water absorption kinetics of three cowpea varieties (Asontem, Hewale and Asomdwee) was studied following the phenomenological models derived from Fick’s law of diffusion. Soaking of seeds from each cowpea variety was carried out for 10 h at four temperatures (30˚C, 40˚C, 50˚C and 60˚C). The saturation moisture content was higher for Asontem (106.9 g water/1000 g dry weight) and Hewale varieties (108.7 g water/1000 g dry weight) and lower for Asomdwee hybrid (100.7 g water/1000 g dry weight), respectively. The proposed Fick’s law of diffusion satisfactorily described the kinetics of water absorption regardless of the variety and temperature. The estimated values for water diffusion coefficient for Asontem, Hewale and Asomdwee varied from 5.12 × 10−10 m2/s to 6.64 × 10−10 m2/s, 3.96 × 10−10 m2/s to 5.12 × 10−10 m2/s, 4.93 × 10−10 m2/s to 6.08 × 10−10 m2/s, respectively. The strong influence of temperature on the water diffusion coefficient was adequately described by an Arrhenius- type equation with activation energy values for Asontem, Hewale and Asomdwee as 7.27 kJ/mol, 7.26 kJ/mol and 6.26 kJ/mol, respectively