3. RESULTS and DISCUSSION
3.1 Physicochemical analysis of Qingjinju seed oils
Table 1 details the physicochemical properties of the Qingjinju seed oils isolated by screw press, solvent, and supercritical CO2 extraction and should be interpreted with respect to these specific techniques. The yield of oil significantly varied based on the extraction process, with solvent extraction providing the greatest quantity (35.07%), followed by screw press (31.04%), and supercritical CO2 extraction (27.69%). These results disagree with those reported by Pradhan et al36, which may reflect differences between the initial oil content of the seed varieties.
Both the specific gravity (20 °C) and the refractive index (25 °C, cP) varied across the different extraction techniques; however, they showed similar patterns with screw press extraction oil (SPO) > supercritical CO2 extraction oil (SCO) > solvent extraction oil (SO). The specific gravity of the oils was significantly different, with values ranging between 0.903 and 0.934 across the different extraction techniques. The high specific gravity of SCO is likely due to the inclusion of seed particulate mixed into the oils during the pressing process. The refractive indices ranged from 1.4660-1.4687, which is in good agreement with the findings of Kiralan et al.37
The distinct extraction methods resulted in notable color differences between the Qingjinju seed oils. The color of the oils processed by screw press, solvent, and supercritical CO2 extraction was atrovirens, reseda and faint yellow, respectively. SPO had a deep color, with a value of 4.0 in the red scale, 74.1 in the yellow scale, and 7.0 in the blue scale, which may indicate that screw pressing allows for the extraction of chlorophyll21.
The average acid and peroxide values of the Qingjinju seed oils ranged from 0.85-1.02 mg KOH/g oil and 4.38-11.94 meq O2/kg oil, respectively. These values are lower than those obtained by Yilmaz et al14 in their examination of lemon seed oil. The method of extraction played a role in the acid and peroxide levels of Qingjinju seed oils, with SPO displaying higher acid (1.02) and peroxide (11.94) values as compared to SO and SCO. These findings were in contrast to those reported by Pradhan et al.36, Moreno et al.21 and Ixtaina et al.38 These differences likely result from the high temperature generated during screw press extraction, which can lead to decomposition of the triglycerides into fatty acids and contribute to the formation of peroxides39.
The iodine number of the Qingjinju seed oils ranged between 107.85 and 118.84 g I2/100 g, which was in good agreement with the values reported by Manaf el at.4 While the iodine numbers of SPO and SO were similar, they were significantly higher than for SCO. As the iodine value is a direct measure of the number of double bonds, the higher iodine number for SPO and SO indicates that these oils contain a greater amount of unsaturated compounds. This conclusion is also supported by the GC-MS analysis of the fatty acids performed in this work.
The saponification values of SPO and SCO were 206.16 mg and 207.69 mg KOH/g oil, respectively. These values are slightly higher than those reported by Anwar el al.15 for citrus seed oils from four different Citrus spp. (180.9 to 198.9 mg KOH/g oil). However, SO had a significantly lower saponification value (170.01 KOH/g oil), indicating that the different extraction methods influence the saponification values, which agrees with the findings of Moreno et al.21
The unsaponifiable values of the Qingjinju seed oils ranged from 0.37% to 0.62% and were significantly different across all three extraction methods. These values are notably less than the unsaponifiable values of limonin seed14 and musk lime seed oils4.