Physicochemical properties of Irvingia gabonensiskernel oil (IGKO)
The physicochemical characteristics of IGKO are shown in Table 3. In terms of IGK oil yield, it was found to be 68.80% (by weight) (see Table 3). This value was higher than oil yield values reported for cottonseed [62], and soybean [63], hence, an indication of its economic benefit and possible industrial application of IGKO. As a result, IGKO could constitute an alternative source of oil for industrial application due to its relatively high oil yield. Similarly, Matos et al. [12] and Zoué et al. [11], reported 73.83 % (in mass) and 69.76 % (in mass), respectively, for Irvingia gabonensis kernel oil. These values were higher than that obtained in this work. The variation in the IGKO yield in this work when compared to those in the literature could be linked to the extraction methods and conditions, in addition to the type of solvent used [56]. Also, this difference in IGKO yield could also be attributed to factors like, geographical location, seed variety and period of harvest [59,64]. From Table 3, it would be seen that the viscosity and acidity of IGKO were 19.37 mm2 S-1 and 5.18 mg KOH/g, respectively. However, the value of the viscosity in this work was found to be lower than 45 mm2S-1 for Irvingia gabonensis kernel oil, but higher than 3.2 mm2 S-1 for the IGK oil biodiesel, as reported by Bello et al. [15]. For the acid value, the IGKO acid value (5.18 mg KOH/g) in this work was found to be lower than 9.40 mg KOH/g, reported by Etong et al. [65], but higher than 4.67 mg KOH/g and 1.2 mg KOH/g, reported by Zoué et al. [11] and Bello et al. [15], respectively. As already stated, the difference in the viscosity and acidity of IGKO in this work when compared to those reported elsewhere could be attributed to the breed of Irvingia gabonensis kernel used [56,59]. This difference in viscosities of IGKO in this work and those in the literature could be due to differences in the extraction temperatures, since temperature significantly affects viscosity [58]. As could be seen in Table 3, the iodine value (IV) of the IGKO (98.75 g/I2/100g oil) in this work was higher than the 32.43 g/I2/100g oil and 4.17 g/I2/100g oil reported by Zoué et al. [11] and Yusuf et al. [66], respectively. The high iodine values of the oil are an indication of the high level of unsaturation nature of the oils. As evident in Table 3, the density and moisture content of IGKO were 900 g/cm3 and 3.75 mg kg-1, respectively. This density was lower than 930 g/cm3, reported by Bello et al. [15]. In case of moisture content, that of IGKO was higher than 0.023 reported by Matos et al. [12]. The difference in the moisture content could be attributed to the initial moisture content of the IGK sample prior to the extraction process, as well as the method of extraction used [67]. Furthermore, the pour and flash points values of IGKO were 17 °C and 285 °C, respectively (see Table 3). These values were lower than 28 °C and 300 °C, respectively, reported by Bello et al. [15] for IGKO. However, the pour point value IGKO was lower than the pour point (-6 °C) values ofIrvingia gabonensis kernel oil biodiesel, while its flash point was higher than that of Irvingia gabonensis kernel oil biodiesel (140 °C) [15]. This high flash point of IGKO in this work is an indication of the safety handling nature of the oil, hence, could easily be stored at room temperature [68]. The dielectric strength (DS) value of Irvingia gabonensis kernel oil (IGKO) was 25.83 KV (Table 3). This value was found to be lower than those of soybean oil (39 KV) [69] and Terminalia catappa kernel oil (30.61 KV) [59], but slightly higher than that of palm kernel oil (25 KV) [69]. Although this value is lower than the minimum requirement of 40 to 60 KV for conventional mineral transformer oil, it is important to know that the DS value of IGKO could as well be improved with further purification and transesterification [70].