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.
Highlights
Cowpea (Vigna unguiculata) is an essential member of the legume family Fabaceae
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
The basic dimensions (length (L), breadth (B) and thickness (T) all in millimeters) of sample seeds from each cowpea variety were determined in triplicate using a digital Vernier caliper with a least count of 0.02 mm for each single seed of 10 seeds sampling before soaking and average value was determined for each sample
Summary
Cowpea (Vigna unguiculata) is an essential member of the legume family Fabaceae. It is widely consumed in many parts of the world including Ghana. For industrial purposes, whether in designing food processing equipment or determining favorable conditions under which soaking can be carried out and how these conditions change with time and temperature, it is necessary to have measurable data which describe the effect of the processing variables on agricultural materials [8] [9] [10]. Several hydration models such as the exponential model, the Peleg’s model, first-order kinetics, Becker’s model among others have been developed by various researchers to predict rehydration of several legume seeds [11] [12] [13].
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