201 / 258
G
olay
&
M
oulin
:
J
ournal of
AOAC I
nternational
V
ol
.
99, N
o
.
1, 2016
217
C18:3 TFA
.—The sum of
trans
isomers from C18:3 in
deodorized vegetable oils (i.e., C18:3
trans
-
9,
cis
-12,
trans
-15;
C18:3
cis
-9,
cis
-12,
trans
-15; C18:3
cis
-9,
trans
-12,
cis
-15; and
C18:3
trans
-9,
cis
-12,
cis
-15).
Total TFA
.—Sum of C18:1 TFA, C18:2 TFA, and C18:3 TFA.
G. Calculations
(
1
)
Calculation of response factors.
—Determine the area of
the peaks attributable to each FAME present in the calibration
standard mixture,
D
(
p
), and calculate
Rf
i
, their respective
response factors relative to the internal standard (C11:0):
=
′ ⋅ ′
′ ⋅ ′
Rf
m A
m A
i
i
O
O i
where
m′
i
= mass fraction of FAME
i
in the calibration standard
solution,
D
(
p
);
A′
O
= peak area of C11:0 in the calibration
standard solution chromatogram;
m′
O
= mass of C11:0 in the
calibration standard solution,
D
(
p
); and
A′
i
= peak area of
FAME
i
in the calibration standard solution chromatogram.
The variation between three injections is optimal when
coefficients of variation are <2.5.
Note
: The response factors calculated for C18:2
n
-6
cis
could
be applied for the quantification of C18:2 CLAs, and those
calculated for C18:3
n
-3
cis
could be applied for C18:3
trans
isomers.
(
2
)
Fatty acids expressed on the product.
—Calculate the
mass fraction of the individual fatty acid components (FA
i
),
expressed in grams FA
i
per 100 g product in the test sample by
using the following equation:
gFA g product
m A Rf S FA
A m
i
o i
i
i
o
=
⋅ ⋅
⋅
⋅
⋅
/ 100
( ) 100
where
m
O
= mass in milligrams of C11:0 internal standard
added to the sample solution
D
(
j
);
A
i
= peak area of FAME
i
in the sample chromatogram;
Rf
i
= response factor, calculated
according to
G
(
1
);
S
i
(FA)
= stoichiometric factor to convert
FAME
i
to FA
i
(Table
2012.13
);
A
O
= peak area of C11:0
internal standard in the sample chromatogram; and
m
= mass in
milligrams of the test portion.
Note
: For powder samples, the result is expressed in grams
FA
i
per 100 g product, which can be converted to reconstituted
liquid product (i.e., 25 g powder dissolved in 200 g water).
Note
: In the case of fatty acids analysis carried out on fat
extracted from foods, the mass of test portion
m
corresponds
to fat and not to the finished product. Consequently, fatty acids
results are expressed in grams fatty acids per 100 g fat, which
can then be converted into grams fatty acids per 100 g product,
with the fat extraction value determined with an appropriate
validated extraction method.
(
3
)
Fatty acids expressed on the total fat.
—Calculate the
mass fraction of the individual components expressed in grams
FA
i
per 100 g fat in the test sample by using the following
equation:
=
⋅
/ 100
/ 100
100
%
gFA g fat
gFA g product
Fat
i
i
Figure 2012.13D. Example of GC chromatogram of the SPIFAN matrix sample infant formula powder, milk-based. Monounsaturated fatty
acids and PUFAs are indicated, counting from the terminal methyl carbon toward the carbonyl carbon (designated as n or ω).
201