Chemistry Reference
In-Depth Information
for measuring TDF. Some of these dilute, alcohol-soluble nondigestible carbohy-
drates do possess physiological characteristics similar to DF, such as fermentation to
short-chain fatty acids, effect on fecal bulking, and transit time. In some cases, they
may be considered “prebiotics.”
At present, there are five approved methods for the determination of nondigest-
ible carbohydrates. These methods can be classified as chromatographic or spectro-
photometric procedures; in general, they all require initial extraction with hot (80°C)
or boiling water and centrifugation in an ultrafiltration device when appropriate. In
2008, a new method was published for the determination of fructo-oligosaccharides
using ion cyclotron resonance mass spectrometry.
1.3.1 Ion Chromatographic Method
1.3.1.1 For Fructans and Fructo Oligosaccharides
Fructans are polysaccharides consists of fructose linked by β-(2-1) bonds with
degree of polymerization (DP) range from 2 to 60 as in inulin, and 2 to 10 as in
fructo-oligosaccharides.
AOAC method 997.08/AACC 32-31
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was the first method approved by AOAC
International and AACC specifically for the determination of fructans and their
oligomers. Test samples are extracted with boiling water; the extract is hydrolyzed
sequentially with amyloglucosidase and inulinase. Free fructose, glucose, and sucrose
are separated and quantified by high-performance anion-exchange chromatography
with pulsed amperometric detection (HPAEC-PAD) in the extract before hydrolysis,
then glucose and fructose after each of the two enzyme hydrolysis steps. Fructan
content in the test sample is calculated by difference from the amount of each sugar
in different solutions.
1.3.1.2 For Polydextrose
Polydextrose is a manufactured polysaccharide prepared by acid catalyzed vac-
uum thermal polymerization of glucose and sorbitol. The average DP is 12 with
range of molecular weight between 162 and 20,000. AOAC method 2000.11
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incor-
porates hot water extraction and ultrafiltration. The filtrate is treated with a mix-
ture of isoamylase, amylogluco-sidase, and fructanase. Polydextrose standards are
treated in similar manner, and used to quantify a high-molecular-weight fraction of
polydextrose using HPAEC-PAD.
1.3.1.3 For trans-Galacto-Oligosaccharides
trans
-Galacto-oligosaccharides (TGOS) are manufactured oligosaccharides pro-
duced from lactose by enzymatic transgalactosylation and with DP range from 2 to 7.
AOAC method 2001.02
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employs hot (80°C) phosphate buffer for the extraction of
TGOS and lactose from test samples. The extract is treated with β-galactosidase to
hydrolyze the di- and oligosaccharides to yield glucose and galactose. Free galactose
