Refining of oils
Crude silflower and sunflower oils were refined by degumming (Diosady et
al., 1982; Ghazani et al., 2013), alkali refining (Suliman et al.,
2013), and bleaching with Fuller’s earth (Soldo et al., 2019). In brief,
crude oil (200 g) was heated to 70 °C under argon, a 64 % aqueous
citric acid solution (1.4 grams) was added to oil, stirred for 30 min,
distilled water (4.0 g) was added, and stirred for another 30 min. After
cooling to room temperature, the gums were removed via centrifugation at
7500 rpm for 10 min, and oil was washed with deionized water (25 ml).
Degummed oil was mixed with 2% sodium hydroxide solution (16 g) at 40
°C with slow agitation for 30 min. After cooling to room temperature,
soap stock was separated by centrifuging at 7500 rpm for 10 min. The oil
was dissolved in hexane (100 ml), washed with deionized water (100 ml)
three times using a separatory funnel, and dried over
MgSO4, filtered, and the solvent was removed using a
rotary evaporator and then a vacuum pump. Fuller’s earth (8.0 g) was
added to the oil and stirred at 40 °C for 40 min under argon. Then, it
was cooled to room temperature and filtered through a thin layer of
celite (Strieder et al., 2017).