Compositional, physico-mechanical and functional properties of two Ghanaian cowpea (<i>Vigna unguiculata</i>) varieties

Abstract

Cowpea (Vigna unguiculata) is a legume that is cultivated throughout Africa and contributes a significant amount of plant-based protein to human diets.  There are many varieties of cowpeas, and these have varying seed characteristics such as shape, size, colour and nutritional properties. The  compositional, physico-mechanical, and functional properties of two new cowpea seed varieties were investigated in order to determine their full food- use potentials as well as key parameters for their postharvest machinery for processing, handling, and storage. The proximate composition of the two cowpea cultivars was determined using standard methods. Physico-mechanical analyses carried out were the hundred-seed weight and volume, bulk  density, true density, size, aspect ratio, surface area, equivalent diameter, porosity and angle of repose. Functional properties determined were cooking  time and water uptake of the grain as well as water and oil absorption, foam capacity and stability, and emulsion capacity and stability of the flour. The  Padi-Tuya variety was longer, broader and thicker than Wang Kae. The results showed both varieties to be useful sources of macronutrients. The  moisture, fat and fibre in Wang Kae were significantly higher (p<0.05) than Padi-Tuya. However, both cowpea varieties had comparable protein levels of  17.7 g/100g. The cooking time, hydration capacities and indices of the two varieties were also significantly different (p<0.05), but their swelling  capacities, swelling and water uptake indices were comparable. Cooking times were 40 and 62 min for Padi-Tuya and Wang Kae, respectively. The water  and oil absorption capacities, as well as the swelling indices, were similar, but their emulsion capacities and stabilities were significantly different (p<0.05)  for the flour. Padi-Tuya had a higher foam capacity, but was less stable, than Wang Kae. The physico-mechanical properties determined would aid in the  design of cleaning, handling and other processing machinery as well as storage facilities for the new cowpeas. The functional and the compositional  parameters would assist in the food formulations.