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.