Properties of silflower oil extracted with hexane
Unhulled silflower seeds were extracted with hexane at 55 °C, and for
side-by-side comparisons, unhulled sunflower seeds were purchased and
extracted under the same conditions. Table 1 shows the oil contents and
properties of silflower oil in comparison with sunflower oil. The oil
content in unhulled silflower seeds
(15.2%, w/w) was slightly lower
than that in unhulled sunflower oil (18.0%, w/w). TPC in silflower oil
was significantly higher (12.3%, w/w) than sunflower oil (4.1%, w/w).
It also had a higher content of total phenolics (1.12 mg GAE/g) than
sunflower oil (0.46 mg GAE/g). In addition to the major components,
triacylglycerols, plant oils contain polar lipids such as phospholipids
and galactolipids, monoacylglycerols, diacylglycerols, free fatty acids,
sterols and sterol derivatives (for example, phytosterols), tocopherols,
carotenoids, chlorophylls, other phytochemicals (Zambelli et al., 2015).
Apparently, silflower oil contained more of these compounds than
sunflower oil. High total phenolics of silflower oil may be beneficial
to its oxidative stability since many phenolic compounds are known to
have antioxidant activity. It is also possible that silflower oil may
contain large amounts of biologically active compounds that are
beneficial to human health, which should be further studied. The ABTS
assay is a widely used method to assess the radical scavenging ability
of antioxidants in oil (Ilyasov et al., 2020; Re et al., 1999). The ABTS
assay of the methanol extract of crude silflower oil was slightly, but
not statistically significantly lower than that of crude sunflower oil
despite having higher total phenolics content.
The fatty acid composition of silflower oil (Table 1) analyzed in this
study is similar to those in previous studies (Evangelista et al., 2023;
Kowalski & Wierciński, 2004) and that in sunflower oil indicating that
this oil has potential as a new edible oil. As shown in Table 1, the
linoleic acid (C18:2, c9,12) and oleic acid (C18:1, c9) contents in
silflower oil (65.53 and 19.86%, respectively) were similar to those in
sunflower oil (65.48% and 22.49%, respectively). Some minor fatty acid
contents were different in the two oils. For example, contents of
myristic acid (C14:0) and palmitic acid (C16:0) were higher in silflower
oil while those of stearic acid (C18:0) and behenic acid (C22:0) were
lower. Total contents of unsaturated fatty acids were similar in the two
oils with 86.2% in silflower oil and 88.5% in sunflower oil.
It should be noted that silflower oil contained 4.34% (the peak area in
GC) squalene. Since this finding is very important for the application
of silflower oil as an alternative source of squalene, the isolation of
squalene was conducted using column chromatography on silica gel.
Squalene was isolated from silflower oil in the yield of 4.89% (w/w),
and its structure was confirmed with 1H NMR in
comparison with previous results (Shi et al., 2019). Squalene has
antioxidant, anticancer, immune stimulating, and emollient activities,
and its use in nutraceutical, cosmetic, pharmaceutical, and vaccine
industries is growing (Rani et al., 2018). Shark liver oil is the most
abundant source of squalene (up to 79%) and has been the most common
source (Lozano-Grande et al., 2018). However, due to the international
concern on overfishing as well as potential risks of polychlorinated
biphenyls (PCBs), heavy metals, and other contaminants in the oil,
consumers and industries are seeking alternative sources. Currently, the
best plant sources of squalene are olive oil (0.15-0.75%) and amaranth
oil (6-8%) (Gutiérrez-Luna et al., 2022; Lozano-Grande et al., 2018).
Therefore, the high content of squalene in silflower oil indicates the
potential application of this oil as a promising alternative source of
squalene.
Analysis of all the tocopherols including α-, β-, γ, and δ-tocopherols
was attempted, but their signals were overlapped with other unknown
signals, and only the level of
α-tocopherol could confidently be determined in this study. The level of
α-tocopherol was lower in silflower oil (305.5 μg/g) than in sunflower
oil (660.1 μg/g). Free fatty acid content in silflower oil (1.00%, w/w)
was higher than in sunflower oil (0.47%, w/w). It contained a very
large amount of chlorophyll (1002.8 mg/kg).