Proximate Composition of Some Selected Legumes and Quality Attributes of Oils Extracted from Soybean, Oil Bean and Groundnut Seeds

Oil contents through analysis of proximate composition of the seeds of six legumes were investigated in order to assess the quality attributes of some of their oils. These legumes were cowpea (Vigna unguiculata), bambara groundnut (Voandzeia subteranea), yam bean (Sphenoostylis stenocarpa), oil bean (Pentaclethra macrophylla), soybean (Glycine max) and groundnut (Arachis hypogaea) seeds. The oil yields ranged from 2.5% in cowpea to 40.3% in groundnut seeds. Crude protein contents ranged from 20.86% in bambara groundnut seeds to 43.02% in soybean seeds indicating they are good sources of protein. Cowpea seeds had highest content (57.76%) in carbohydrate, followed by yam bean (56.54%) and bambara groundnut (51.64%), while oil bean had the lowest value of 6.92%. The physicochemical properties of the oils from soybean, oil bean and groundnut seeds were further examined since their oil yields were above 10.00%. Seventy grams of oil in each case were extracted from these legumes for these analyses. The specific gravity ranged from 0.910 in oil bean oil to 0.917 in soybean oil. Oil bean oil, with highest values in moisture content (0.75 %) and peroxide value (21.2 mg/g oil) had highest saponification number of 306.86 mg/g oil while soybean oil with lowest values both in moisture content (0.43 %) and peroxide value (9.80 mg/g oil) had the lowest saponification number of 187.94 mg/g oil. Free fatty acid ranged from 0.17 in soybean oil to 0.48 in groundnut oil. Iodine value was highest (98.22 mg/100g) in soybean oil, followed by oil bean oil (98.22 mg/100g) and was lowest (93.40 mg/100g) in groundnut oil. These results obtained highlighted the potentials of these three oils in the manufacture of soaps, cosmetics, paints, confectioneries, margarines and edible oils. The results also maintained that soybean oil exhibited the best physicochemical properties amongst them and thus could be used better as edible oil and for industrial applications.