Compositional evaluation of some cowpea varieties and some under-utilized edible legumes in Nigeria

The nutritive potentials of some cowpea varieties such as Ife Brown, Ife Bimpe, IT84E-124, K59 and TVX716 and some under-utilized edible legumes grown in Nigeria such as pigeon pea (Cajanus cajan), lima bean (Phaseolus lunatus), lablab bean (Dolichos lablab), mucuna bean (Mucuna sp.) and Sphenostilis sternocarpa have been evaluated with respect to their proximate chemical composition, mineral content and some endogenous toxic constituents. The cowpea varieties contained on the average 22.5 g crude protein (CP), 2.60 g crude fibre (CF), 5.89 g either extract (EE) and 3.36 g ash/100 g DM while the under-utilized legumes contained 21.7, 6.10, 2.86, and 3.56 g/100 g DM for CP, CF, EE and ash respectively. Distinct varietal differences were observed for EE values as indicated by the coefficients of variation (CV) of 102% for cowpea and 60.8% for the under-utilized legumes. The CF content of the under-utilized legumes were generally higher than those of the cowpea varieties. Potassium was the most abundant mineral in both the cowpea varieties and the under-utilized legumes with mean values of 1.45 and 1.66% respectively, while P was the least abundant with 13.1 and 8.50 ppm, respectively. There were marked intra-varietal differences in the P content as shown by the high CV of 84.0 and 73.9% for the cowpea varieties and the other legumes. The cowpea varieties generally had higher levels of thioglucosides, trypsin inhibitor activity (TIA) and lower haemagglutinating activity (mean values of thioglucosides: 3.86%, of TIA: 13.9 mg/g protein and of haemagglutinating activity: 13.0 HU/mg N respectively), than the under-utilized legumes with mean respective values of 1.22%, 9.84 mg/g protein and 22.7 HU/mg N. The nutritional implications of these anti-nutritional components were discussed and some reasons adduced for the under-utilization of some of these legumes inspite of their apparent similarity in nutritional quality to the more commonly consumed grain legumes.