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United States Department of Agriculture

Agricultural Research Service

Title: Determination of Complex Carbohydrate Fractions in Foods

Author
item Li, Betty

Submitted to: Association Official Analytical Chemists Annual Intrl Meeting & Exposition
Publication Type: Proceedings
Publication Acceptance Date: December 10, 1996
Publication Date: N/A

Interpretive Summary: For a number of years, "Dietary Guidelines for Americans" has been recommending eating more foods containing complex carbohydrates (CC), without providing a clear definition what they are. Are they only referring to starches or starches and dietary fiber? During the past 2 years, nutritionists, food analysts, and food manufacturers have begun to search for a workable definition for this term along with practical analytical methods. Based on the definitions given by the National Research Council in "Recommended Dietary Allowances", The sum of starches and dietary fiber represents complex carbohydrates. Based on this definition, we have a method which separates half gram of freeze-dry food sample into various carbohydrate fractions; namely, sugars, starches, and total dietary fiber. Now, values for CC can be calculated from the analytical data on starches and dietary fiber. The method was used to analyze a variety of high consumption foods, and some sample data will be presented in this Workshop. This method will be useful to everyone who needs carbohydrate data for nutrition labelling , clinical studies, and other research on diet and health. The method is more cost effective and less labor intensive compared to any existing methods, which still needs further modifications.

Technical Abstract: A general scheme has been developed to determine sugars, starches, total dietary fiber, and dietary fiber polysaccharides in a half-gram freeze dried food sample. Triplicate samples are weighed into teflon tubes; free sugars (mono- and disaccharides) are extracted into 80% methanol and analyzed on a gas-liquid chromatograph (GLC). The residues after 80% methanol extraction are incubated with amyloglucosidase and hydrolyzates are removed for glucose determination by GLC. Starch content is calculated as glucose (g/100 g) x 0.9. The remaining hydrolyzates are diluted with 95% ethanol, filtered through glass crucibles matted with celite filter aid. The residues are dried and weighed. One of the triplicate residues is analyzed for crude protein, and the second one for ash. The third residue is hydrolyzed in H2SO4; analyzed for neutral sugars on GLC and uronic acids spectrophotometrically. Total dietary fiber content is calculated as the residue weight corrected for residual protein and ash, and dietary fiber polysaccharides are the sum of neutral sugars and uronic acids. According to this scheme, complex carbohydrates are found in the fractions represented by starch, total dietary fiber, and dietary fiber polysaccharides. Data will be presented on the contents of these complex carbohydrate fractions of some frequently consumed foods.

Last Modified: 11/26/2014
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