Chemical composition of selected Nigerian oil seeds and physicochemical properties of the oil extracts

Proximate composition, energy content and mineral concentrations of oil seeds used in the preparation of Nigerian diets were investigated. The paper also reports the physicochemical characteristics of the oil extracts from the seeds. Moisture content (on dry weight basis) was highest (23.13±0.44%) in coconut seeds (CNS), followed by palm kernel seeds (PKS) (14.26±0.35%) but was lowest (4.12±0.95%) in melon seeds (MS). Ash was highest (3.20±0.40%) in castor seeds (CS) followed by groundnut seeds (GNS) with a value of 2.77±0.65% and was lowest (0.43±0.32%) in CNS. Protein ranged from 6.94±0.10% in PKS to 26.5±0.27% in GNS. Dikanut seed (DNS) had the highest crude fat of 62.80±2.41%, followed by CS (57.33±1.63%), and the lowest value of 40.83±0.50% in GNS. Values for MS, oil bean seeds (OBS) and PKS did not differ significantly. Total carbohydrates were generally low in all the seeds and ranged from 12.5±0.94% in OBS to 26.9±1.01% in CNS. The energy content, in kilocalories, per 100g sample, was highest in DNS (688) followed by MS (643) and was lowest in CNS (516). The oil seeds were found to be good sources of minerals. Copper, potassium, sodium and sulphate were highest in OBS, chloride was highest in PKS; zinc and phosphate were highest in CS while iron ranged from 0.130±0.001 in GNS to 0.489±0.00l mg/100 g in CNS. The physical properties of the oil extracts showed the state to be liquid at room temperature (29±1 °C) and the colour to be pale-yellow or golden-yellow, in general. Melting point was highest in MS oil and lowest in PKS oil while setting point was highest in DNS oil, followed by CNS oil and lowest in MS oil (4.67±0.3 °C). Specific gravity ranged from 0.87 in PKS oil to 0.98 in MS oil. Among chemical properties of the oil extracts, acid value, saponification number, iodine number, percent free fatty acid, peroxide value and unsaponifiable matter were, respectively, highest in CS, MS, PKS, CS, DNS/CNS and GNS oils while the lowest values were, respectively, obtained in OBS, CS, GNS, OBS, PKS and OBS oils. It can be inferred that the oil seeds investigated are good sources of crude fat, crude protein, ash, energy and minerals. The oil extracts exhibited good physicochemical properties and could be useful as edible oils and for industrial applications.