Chemistry Reference
In-Depth Information
transform ion cyclotron resonance mass spectrometry. The method was used to mon-
itor the consumption of fructo-oligosaccharides in bacterial fermentation samples to
better understand the role of inulin and FOS as prebiotics.
1.4 NEEDs
1.4.1 reliable Methods for Determining lignin
as a Component of Dietary Fiber
In any enzymatic-gravimetric method, DF as oligo- and polysaccharides that are
nonhydrolyzable by the specific enzymes are usually recovered along with lignin and
other associated substances, such as waxes, cutin, and suberin from 78 percent alco-
hol. In the enzymatic-chemical method, only the constituent sugars and lignin rep-
resent DF. However, there is no accurate method for routine measurement of lignin,
whose structure as a phenyl-propanoid polymer has not been well defined. Klason
lignin determined by AOAC method 994.13, as the acid insoluble organic matter in
the DF residue, may include some tannins and Maillard reaction products. A modi-
fied permanganate method has been shown to be more reproducible and the values
are lower when compared with those obtained after acid detergent fiber extraction
followed by permanganate treatment or after Klason lignin treatment.
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1.4.2 Methods to Determine resistant starch,
Naturally occurring and Added
The fraction of starch that escapes digestion in the small intestine and is fer-
mented in the large intestine is known as resistant starch (RS).
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Analytically, the
amount of RS isolated as part of DF varies depending on the food and the method.
At present, all AOAC methods for TDF include a certain amount of RS in their DF
values for starchy foods. AOAC method 2002.02/AACC method 32-40
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specifically
measures RS. Test samples are incubated with a mixture of pancreatic α-amylase
and amyloglucosidase at 37°C for 16 hours. A pellet is obtained by centrifugation,
then dissolved in 2
M
KOH; the alkaline solution is neutralized with acetate buf-
fer, and treated with amyloglucosidase. The absorbance of glucose in the enzyme
hydrolyzate is measured at 510 nm after the addition of glucose oxidase-peroxidase
reagent. RS content is calculated from the amount of glucose in the hydrolyzate.
1.4.3 Integrated Methods to Determine Alcohol-soluble and
Alcohol-Insoluble Nondigestible Carbohydrates
With the exception of AOAC method 2001.03 for the determination of resistant
maltodextrins and TDF, all the existing methods mentioned above are applicable for
the determination of either alcohol-soluble or alcohol-insoluble nondigestible carbo-
hydrates, but not both simultaneously in the same test portion. Integrated methods
ought to be developed to do just that. Such methods should also be able to quantify
