Comparative Evaluation of Physicochemical Properties and Fatty Acid Composition of Selected Indigenous Plant Oils

Abstract

The need to meet the human consumption and industrial demand of oils has continued to attract research interests to unravel other alternative sources especially under-utilized and agro-waste source. Physicochemical properties and fatty acid profiles of oil extracts of some indigenous under-utilized seeds were compared with some conventional oils. Soxhlet extraction of the crushed seed samples was carried out using N-hexane as solvent. The density, viscosity, saponification value (SV), iodine value (IV), peroxide value (PV) of the oil extracts were studied as well as gas chromatographic profile of the fatty acids to evaluate their compositional quality. No significant differences were observed in the refractive index (1.46) and specific gravity (0.95 – 1.10) of all the test samples as well as viscosity of oils from groundnut, African nutmeg, oil bean and palm kernel in comparison with the reference olive oil. Iodine values of the test samples which were significantly lower than the standard oil (129.42 ± 0.16) fell in the range of 62.50 ± 0.21 and 112.846 ± 0.24. Significantly high saponification values of 613.17 ± 23.67 and 566. 45 ± 25.01 were obtained in oil bean and groundnut samples respectively. Free fatty acid (FFA) content of oil extracts of African nutmeg, watermelon and cashew nut were significantly higher than that of olive oil (4.44%) with values corresponding to 30.58 ± 0.16%, 9.99 ± 0.09% and 4.68 ± 0.06% respectively. The sterol contents of the test samples except African nutmeg oil (194.70 ± 2.95 ppm) were significantly below the sterol content of olive oil (21.11 ± 0.16 ppm). All the test samples had higher peroxide values than olive oil (3.228 ± 0.13) with African nutmeg oil possessing the highest peroxide value of 21.857 ± 0.20 mEq/kg. However, the thiobarbaturic acid (TBA) of the test samples were comparable to that of olive oil (0.76 ±0.04) except that of cashew nut oil which was significantly higher (5.17). High percentage saturated fatty acid was predominant in cashew, soybean, watermelon, nutmeg, palm kernel and oil bean while groundnut oil had significantly higher polyunsaturated fatty acid than olive oil. Among the polyunsaturated fatty acids, linoleic was predominant in soybean, oil bean, palm kernel and groundnut oil extracts though significantly highest in olive oil and absent in watermelon. Significant amount of oleic acid in groundnut, cashew, palm kernel, oil bean, watermelon and soybean oil extracts compared to olive oil content is an indication that the various oils could serve as anti-inflammatory agent among other benefits. The various oil extract from the plant samples showed beneficial properties that could be harnessed for domestic and industrial utilization.