Preliminary evaluation of physical and chemical properties of Piper guineense and Xylopia aethiopica seed oils.
Piper guineense and Xylopia aethiopica are commonly used as spices and traditional medicine in Southern Nigeria. The nutritional and health potential of their seed oils were evaluated by the study using standard methods. Values of all measured properties of the oil samples, except for peroxide and pH, were significantly (p < 0.05) different. The peroxide value of Piper guineense oil sample was 0.92 ± 0.01 mEq/Kg while Xylopia aethiopica oil gave a peroxide value of 13.35 ± 0.05 mEq/Kg which suggested that some level of oxidation might have occurred in the Xylopia aethiopica oil between the time of extraction and analysis. The iodine, saponification and ester values of Piper guineense oil sample were 13.66 ±0.70 gI2/100g; 13.18 ± 0.98 mgKOH/g and 154.97 ±1.10 mgKOH/g whereas those of Xylopia aethiopica oil were 75.30 ± 1.83 gI2/100g; 171.82 ± 5.07 mgKOH/g and 108.70 ± 1.50 mgKOH/g, respectively. However, their acid values (21.48 ± 1.21 mgKOH/g for Piper guineense and 16.85 ± 1.64 mgKOH/g for Xylopia aethiopica) and free fatty acid values (10.74 ± 0.82 mgKOH/g for Piper guineense and 8.43 ± 0.41 mgKOH/g for Xylopia aethiopica) were low whereas their unsaponifiable matter values were correspondingly high (69.16 ± 1.03% for Piper guineense and 19.16 ± 0.92% for Xylopia aethiopica) when compared to those of some popular seed oils. Their pH values at 25oC were mildly acidic (5.76 ± 0.08 for Piper guineense and 5.10 ± 0.07 for Xylopia aethiopica). Some level of antioxidant activity was observed in the two oil samples. Thus, the oil samples investigated could be classified as non-drying.