CHARACTERIZATION AND COMPARATIVE ASSESSMENT OF THE PHYSICO-CHEMICAL PROPERTIES OF COCONUT (Cocos nucifera) AND WALNUT (Tetracarpidium conophorum) OILS
Characterization and comparative assessment of Cocos nucifera and Tetracarpidium conophorum seeds and the oils were evaluated in this work using standard techniques. The percentage proximate analysis of the samples revealed that the moisture, ash, fibre and protein contents of coconut sample were significantly lower (p<0.05) than that of walnut while the fat, carbohydrate and energy value of walnut sample were significantly lower (p<0.05) than that of coconut sample. The phytochemical constituents of the samples were also qualitatively and quantitatively analysed. The quantitative phytochemical constituents of the samples showed that the amount of alkaloids (2.29 mg/100g), saponins (8.07 mg/100g) and glycosides (2.19 mg/100g) were significantly higher (p<0.05) in walnut than that of coconut sample. On the other hand, the amount of reducing sugar (10.07 mg/100g), flavanoid (1.864 mg/100g) and tannins (2.77 mg/100g) were significantly increased (p<0.05) in coconut sample when compared with that of walnut sample. Soluble carbohydrate, hydrogen cyanide and tepernoids show no significant differences (p>0.05) between the samples. The mineral analysis of the seed samples revealed that the manganese (3.20±0.02 mg/100g), zinc (6.78±0.08 mg/100g), iron (2.89±0.02 mg/100g), phosphorus (265.92±0.32 mg/100g) and calcium (44.99±0.14 mg/100g) contents of the walnut sample were significantly higher (p<0.05) than that of the coconut sample while the opposite was the case when magnesium, potassium and sodium are considered. However, the amount of copper (1.24±0.02 mg/100g and 1.87±0.02 mg/100g) observed showed no significant difference (p>0.05) between the samples. The result of the vitamin analysis revealed an appreciable amount of vitamin A (3.12±0.06 mg/100g and 2.24±0.06 mg/100g) and vitamin C (14.71±0.02 mg/100g and 5.08±0.00 mg/100g) in both Cocos nucifera and Tetracarpidium conophorum samples. However, it was observed that walnut sample contains a great amount of vitamin E (70.00±0.08mg/100g). The result also revealed that the amount of vitamin A, C, B2 and B6 were significantly lower (p<0.05) in walnut sample than that of coconut sample while vitamin E content significantly increased (p<0.05) in walnut sample than that of coconut sample. Other vitamins detected in the respective samples though in trace amount, were reported in Table 10. The oils of Cocos nucifera and Tetracarpidium conophorum were extracted by cold method and the percentage oil yields gave 42.5% and 24% respectively. The physicochemical properties of the coconut and walnut oils were determined and the result revealed that the oils have agreeable odour with a colour, yellow and golden yellow, specific gravity of 0.89 and 0.91, refractive index of 1.46 and 1.48, viscosity of 10.96 mm2/s and 21.69 mm2/s at 40oC, acid value of 5.54 mgKOH/g and 19.2 mgKOH/g, saponification value of 267.90 mgKOH/g and 186.95 mgKOH/g, peroxide value of 0.13 meq/kg and 0.93 meq/kg, iodine value of 7.87 mI2/g and 29.44 mI2/g for Cocos nucifera and Tetracarpidium conophorum respectively. All the physical properties observed for the oils were in agreement with those recommended by Codex Standard for Vegetable oils (1999) and as such indicate edibility. The chemical properties of oils extracted from Cocos nucifera and Tetracarpidium conophorum seeds were compared well with selected commercially available oils in the Nigerian market.