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1576
H
aselberger
&
J
acobs
:
J
ournal of
AOAC I
nternational
V
ol
. 99, N
o
. 6, 2016
H
ase berger & Jacobs:
J
urnal of
AOAC I
nternational
V
ol.
99, N
o
. 6, 2016
1
Determination of Fructans in Infant, Adult, and Pediatric
Nutritional Formulas: Single-Laboratory Validation, First
Action 2016.06
Philip Haselberger
and
Wesley A. Jacobs
Abbott Nutrition, 3300 Stelzer Rd, Columbus, OH 43219
Received June 16, 2016. Accepted by SG July 1, 2016.
This method was approved by the AOAC Expert Review Panel for
SPIFAN Nutrient Methods as First Action.
The Expert Review Panel for SPIFAN Nutrient Methods invites
method users to provide feedback on the First Action methods.
Feedback from method users will help verify that the methods are
fit-for-purpose and are critical for gaining global recognition and
acceptance of the methods. Comments can be sent directly to the
corresponding author or
methodfeedback@aoac.org.Corresponding author’s e-mail:
philip.haselberger@abbott.comDOI: 10.5740/jaoacint.16-0190
INFANT FORMULA AND ADULT NUTRITIONALS
A method for fructan analysis designed to comply
with AOAC
Standard Method Performance
Requirements
(SMPR
®
) 2014.002 is described. It
is closely related to existing methods for fructan
analysis, including AOAC 997.08 and 999.03,
as well as a method previously published by
Cuany et al. This new method achieves LOQ of
0.03% fructan on a ready-to-feed (RTF) basis with
mean recoveries ranging from 93 to 108% in the
presence of up to 9% sucrose (even at the 0.03%
level of fructan). Repeatability ranged from 1.09
to 3.67%. Intermediate precision ranged from 2.46
to 6.79%. Sample preparation for quantitative
analysis is simplified compared to some of the
existing methodologies. The method incorporates
a qualitative profile analysis to determine fructan
size category. This allows assignment of appropriate
correction factors without independent knowledge of
fructan type.
A
s defined in AOAC SMPR 2014.002 (1), fructan is a
general term that encompasses fructooligosaccharides,
oligofructose, and inulin. These are all referred to as
inulin-type fructans, despite the fact that ingredient sources
relevant to this category may not necessarily be derived from
inulin. These carbohydrates act as dietary fiber with prebiotic
benefits and range in size from a degree of polymerization
(DP) of 2 to 100. Fructans of this type are represented by two
general structural forms (Figure 1).
Fructooligosaccharides
and intact inulin materials are comprised almost exclusively
of GF
n
type molecules (i.e., an oligosaccharide composed
of a chain of n fructose molecules with a terminal glucose
molecule). Oligofructose and materials that are a mix of
intact inulin and oligofructose contain both GF
n
and F
m
type
molecules (F
m
meaning an oligosaccharide composed of a
chain of m fructose molecules only). GF
n
structures are non-
reducing while F
m
structures are, and the reducing nature of the
latter has significant ramifications for methodology capable of
determining both types.
Because relevant ingredients are all mixtures of varying
complexity, methodology based on direct determination of all
the fructan forms that are present is of limited utility, especially
in complex nutritional formulations. High-temperature GC
methods (2, 3) and HPAEC/PAD profiling methods (4, 5) have
been reported, but the lack of suitable individual reference
standards limits the usefulness of methods attempting direct
quantitative determination of the entire fructan profile, as does
the potential presence of a complex non-fructan carbohydrate
system. In addition, the direct profiling methods are generally
limited to species of DP <5–8 (for the methods noted above).
In one approach, profiling of test samples is used to tentatively
identify the specific fructan ingredient. Subsequent quantitative
analysis is then based on determination of one or a few
“marker” components using a calibration curve constructed
from analysis of actual commodity samples. While this type of
strategy can produce accurate results under ideal circumstances,
there are significant practical limitations, one of which is the
growing diversity of ingredients (and suppliers). It also fails to
account for the fact that even lot-to-lot differences in ingredient
fructan profile is a potential source of uncertainty as well as the
possibility that the final fructan profile in a food product may
differ from that in the original ingredient due to changes incurred
during processing.As a result of the complexities associated with
direct determination, methods generally emphasize a strategy
based on determination of the monosaccharides released from
fructans by enzymatic hydrolysis and subsequent calculation of
fructan content using appropriate correction factors.
Methods basedonpost hydrolysis analysisofmonosaccharides
may rely on determination of both glucose and fructose or
fructose only. Both AOAC
997.08
(6) and AOAC
999.03
(7)
determine glucose
and
fructose. In such methods the only
correction factor required is for water added during hydrolysis:
C
fructan
= k
W
(C
G,f
+ C
F,f
)
(1)
where C
fructan
=
fructan concentration
;
C
G,f
= concentration
of
glucose from fr ct ; C
F,f
= concentration of fructose from
fructan.
k
w
= correction factor for water = 0.9 +
0.1
DP
avg
where
DP
avg
= average DP of fructan.
The presence of reducing sugars negatively impacts AOAC
method
999.03
(7). Because the reducing end of the molecule
of F
m
forms is converted to a sugar alcohol, it will not react with
the PAHBAH reagent (
p
-hydroxybenzoic acid hydrazide) used
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