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H
aselberger
&
J
acobs
:
J
ournal of
AOAC I
nternational
V
ol
.
99, N
o
. 6, 2016
1577
2
H
aselberger & Jacobs
: J
ournal of
AOAC I
nternati nal
Vol. 99, No. 6, 2016
in the post hydrolysis colorimetric determination of fructan-
derived monosaccharides. As a result, the total fructan content
will be underestimated. AOAC
997.08
relies on a correction for
the monosaccharides released by other carbohydrates, including
sucrose (6). This results in compromised precision because of
the error propagation in the background corrections which
generally limits the usefulness of method
997.08
, or similar
methods, to samples with a sucrose:fructan ratio of 3:1 or 4:1
(or less; 8, 9).
Methods based on determination of fructan from only
fructose require two correction factors:
C
fructan
= k
W
k
G
(C
F,f
)
(2)
k
G
= correction for glucose content =
q
+1
q
where q = average fructose to glucose ratio of fructans.
For the special case of GF
n
fructans:
�
G
= � ��
avg
��
���
-1
�
(3)
which makes the overall correction (
k
W
k
G
), in terms of
DP
avg
:
�
W
�
G
= � 0.9��
avg
+ 0.1
��
���
-1
�
(4)
The method of Cuany et al., recognizes that, when sodium
borohydride treatment is used to eliminate free reducing sugars,
Equation 4 applies to fructans of both GF
n
and F
m
type because,
if fructan is calculated on the basis of fructose only, the terminal
glycosyl residue is lost for all forms, just as it would be for
only GF
n
species (10). The shortcoming of this method, as
with all methods to date, is the need to either have independent
knowledge of the fructan ingredient (which would allow
selection of a specific correction factor) or application of a
common factor regardless of fructan type.
The method presented
here is based on the chemistry used in the Cuany method (10),
but with a few distinct differences, the most important being the
addition of a procedure for selecting the appropriate correction
factor to be applied for calculating the total fructan content and
significant procedural simplification by eliminating the need for
SPE cleanup.
Table 2016.06A. Total fructan single-laboratory validation data: precision
Sample type
No. of replicates Mean, g/100g, RTF
a
SD
r
RSD
r
, % SD
IP
b
RSD
IP
, %
c
Materials from SPIFAN sample kit
Child formula powder, placebo
12
d
0.270
0.0055
2.03
0.01547
5.73
Toddler formula powder, milk based
12
d
0.233
0.0080
3.42
0.00806
3.46
Infant formula powder, milk based
12
d
0.283
0.0059
2.09
0.00696
2.46
Child formula powder
12
d
0.277
0.0072
2.61
0.01238
4.47
Infant formula powder with FOS/GOS
e
12
d
0.036
0.0008
2.14
0.00117
3.29
Adult nutritional RTF high fat
12
d
0.500
0.0184
3.67
0.03395
6.79
Abbott Nutrition in-house materials
Infant formula powder, soy based
40
f
0.153
0.0025
1.64
0.00442
2.89
Adult nutritional powder
40
f
0.434
0.0060
1.38
0.01167
2.69
Pediatric powder, milk based
40
f
0.230
0.0052
2.24
0.00892
3.88
Control powder, milk based
60
g
0.370
0.0040
1.09
0.00951
2.57
a
RTF = Ready-to-feed.
b
SD
IP
= Standard deviation (intermediate precision).
c
RSD
IP
= Relative standard deviation (intermediate precision).
d
Duplicates on each of 6 days, one laboratory.
e
FOS/GOS = Fructooligosaccharides/galactooligosaccharides.
f
Duplicates on each of 10 days, in each of two laboratories.
g
Duplicates on each of 10 days, in each of three laboratories.
Figure 1. General formulae for the two major inulin-type fructans relevant to SMPR 2014.002.
Figure 1. General formulae for the two major inulin type fructans relevant to SMPR 2014.02
GF
�
Type: (� − DFru� − (2 → 1))
�
− � − D − Fru� − (2 → 1) − � − D − Glc�
F
�
Type: (� − DFru� − (2 → 1))
�
− (2 → 1)
-
D
- Fru
f
Fru
f
= fructofuranose
Glc
p
= glucopyranose
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