2.3.2. Fatty acid composition
The fatty acid methyl esters were determined by gas chromatography (GC), based on the AOCS Official Method Ce 1–62.
Boron trifluoride in methanol was used as the methylating agent.
The resulting fatty acid methyl esters (FAME) were analysed on a
PU 4410 gas chromatograph (Philips, UK), using a capillary column
RTX-2330 that was 105 m in length with a diameter of 0.25 mm i.d.
and a film thickness of 0.2lm. The detector (FID) and injection
temperatures were 260C. The column temperature ranged from
160C (30 min.) to 180C (17 min.) at 3C/min. and to 220C
(15 min.) at 5C/min. Helium was the carrier gas. The Star Chromatography Workstation (version 6.6) with software from Varian
was used for the data handling system. The fatty acid composition
was expressed as the percentage shares of the total fatty acids calculated using the integrated peak areas of the FAMEs identified in
the samples.
Oil degradation during frying decreased the levels of polyunsaturated fatty acid and increased the saturated fatty acid content.
The losses of polyunsaturated fatty acids (defined as changes to
the unsaturation ratio of C18:2 and C16:0), in relation to the initial
summary content of these fatty acids in fresh oils, were calculated
according to:
LC18:2
C16:0
¼
C18:2
C16:0
0C18:2
C16:0
f
C18:2
C16:0
0
where C 18:2 and C 16:0 are the percentage shares of fatty acids, ‘f’
represents a thermally treated oil and ‘0’ is the initial oil.