Preparation of stripped oils
To avoid the influence of the minor compounds in oil such as
tocopherols, phospholipids, free fatty acids, and mono- and
diacylglycerols, stripped oils were used in this study. Stripped oils
were prepared using the previously reported method (Hwang et al., 2019).
In brief, a column (5.5 cm i.d., 55 cm length) was prepared with hexane
(500 ml) and dry aluminum oxide (333 g). Sand was added to make a thin
layer on top of aluminum oxide. Oil (500 g) dissolved in hexane (about
500 ml) was added into the column and eluted to a 2 L round-bottom flask
wrapped in aluminum foil under argon blown into the flask. After
completion of elution, hexane (800 ml) was added into the column, and
the oil/hexane mixture was collected in the flask. Hexane was removed
using a rotary evaporator for 2 h at 30-35 ºC followed by drying under
high vacuum for 2 days. HPLC was used to confirm the removal of
tocopherols and other polar compounds in oil. Stripped oils were stored
at -20 ºC under argon, and the storage studies started within a week.