2.2. Fatty Acid Composition
Soybean oil was derivatized to fatty acid methyl esters (FAME) as
described by Kiefer (Kiefer, 1997), then analyzed with GC according to
AOAC Official Method 996.06 (AOAC, 2005). A gas chromatograph (GC-2010,
Shimadzu) was used with a polar ionic liquid capillary column SLB-IL60
30 m x 0.25 mm x 0.20 μm (Sigma-Aldrich, St. Louis, MO), and a flame
ionization detector (FID) at 280°C. Helium was used as the carrier gas
with a flow rate of 1 mL/min. The column temperature was programmed from
150°C to 280°C at a heating rate of 5°C/min. A volume of 1L was
injected, with a split mode of 50:1. Supelco 37-component FAME mix
10mg/mL (Sigma-Aldrich, St. Louis, MO, USA) was used as an external
fatty acid standard to identify the components. Dodecanoic acid
(Sigma-Aldrich, St. Louis, MO) was added as an internal standard.
SLB-IL60 column allows separating oleic acid (C18:1) with the double
bond in 9c or 11c position in the hydrocarbon chain, being 11c a small
fraction of monounsaturated fatty acids (MUFA).
The insoluble fraction in hexane was quantified by the amount of sample
used for fatty acid composition analysis. During derivatization of the
triglycerides into fatty acid methyl esters, a fraction of the treated
sample did not dissolve completely. The filtered (0.2 \(\mu\)m) samples
were injected into the GC, and the insoluble part was quantified as
reported elsewhere (AOAC, 2005).