3.2 Nutrient substances of Qingjinju seed oils
Qingjinju seed oils can be utilized as a source of oil for human
consumption. Table 2 shows the nutrient substances of
the
Qingjinju
seed oils obtained by different extraction methods.
β-sitosterol is the main sterol in
vegetable oils. The β-sitosterol content of the Qingjinju seed oils was
1776-1947 mg/kg, which is higher than observed for oils from C.
aurantifolia or C.
grandis 18.
Limonoids are unique substances with highly oxygenated triterpenoid
backbones and are only found in the Rutaceae and
Meliaceae40 families.
Citrus limonoids have been reported to display
anticarcinogenic41activity and have been suggested as natural chemo preventatives or
nutraceuticals42.
Limonin and nomilin are the major
limonoids and are the primary contributors to the bitterness of citrus
fruits and products.
The limonin and nomilin content in
the Qingjinju seed oils significantly varied across the extraction
methods. The limonin content in SO is 722.49
mg/kg, which is 4.22 and 4.90 times
less than SCO and SPO, respectively. The nomilin content in SO is 65.02
mg/kg, which is 10.35 and 8.23 times less than SCO and SPO,
respectively. This decreased limonoid content may be due to the
decomposition of limonin and nomilin during the long exposure to high
temperatures in the solvent extraction. Citrus oils are generally
characterized by a high percentage of
limonin43-44.
Interestingly, the content of limonin and nomilin in the Qingjinju seed
oils was higher than that of other citrus
fruits42.
The flavonoids in the Qingjinju are reported to be
3´,5´-di-C-β-glucopyranosylphloretin, naringin, and hesperidin, and the
total flavonoid content in peel ranges from 1168 to 1888 mg/100
g45. The total
flavonoid content in the Qingjinju
seed oils was greatest for solvent extraction (28.66 mg/mL), followed by
screw press (26.25 mg/mL) and
supercritical CO2 (24.89 mg/mL) extraction. Notably, the
total flavonoid content in the Qingjinju seed oils was higher than that
reported for Moringa oleifera seed oil (18.24
mg/g)46, which has been
valued for its medicinal properties. This suggests that the Qingjinju
seed oils may also display beneficial antioxidant activity and could be
applied for the natural management of various chronic diseases.
The α-tocopherol content of the
Qingjinju seed oils ranged from 171.68 to 202.70 mg/kg, which was higher
than lemon (155-110
mg/kg)14, mitha (26.4
mg/kg)15, and tangerine
(116.74 mg/kg)47 seed
oil, but lower than grapefruit (380 mg/kg), mussami (220 mg/kg), or
kinnow (557.82 mg/kg)15seed oil. The α-tocopherol content varied significantly based on the
extraction method, which agrees with the findings of Malacrida et
al.47
The total phenolic content of the Qingjinju seed oils ranged from 3.83
to 6.25 mg/kg, which was lower than mandarin, orange, lemon, or
tangerine seed oils19,
47. This difference can be attributed to
both the chemical composition of the different Citrus spp. and
the manner in which the results were obtained. There were significant
differences between total phenolic content of the oils obtained using
the different extraction methods, which is in agreement with results
reported by Mustafa el
al.37 The total
phenolic content of SCO was 6.25 mg/kg, which was 1.2 and 1.6 times
higher than SPO and SO, respectively. Overall, screw press and
supercritical CO2 extraction outperformed solvent
extraction in obtaining nutrient substances from Qingjinju seeds.