Methodology Development

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The McGovern commission recommended that FDA establish a definition of complex carbohydrates. The FDA methodology for measuring complex carbohydrates is determined by summing the total dietary fiber and available starch measured in the sample. Using 80% aqueous ethanol simple carbohydrates (sugars

' Leon Prosky and Susan Sungsoo Cho

Lineback et al.

and low-molecular-weight dextrins) are removed from the food to be analyzed. Fat is extracted if the food contains more than 10% fat.

Duplicate samples of the de-sugared, sugar- and fat-extracted food are treated with a heat-stable amylase to degrade its starch. Each sample is then digested with a protease and an amyloglucosidase mixture to remove protein and starch. Incubation is performed under conditions specified in the AOAC International current method for dietary fiber in food and food products. After the addition of four volumes of ethanol, each sample is filtered. The filtrate is collected and set aside for analysis of available starch content. The residue collected on the filter is washed with ethanol and acetone to remove any remaining low-molecular-weight materials, dried, and weighed.

Total dietary fiber is calculated after correction for the protein and ash contents of the collected residue. The available starch content of the original food is calculated from the glucose content of the filtrate set aside after the addition of four volumes of ethanol. The collected filtrate is evaporated before various spectrophotometric or chromatographic procedures determine its glucose content. Spectrophotometry procedures include either an ultraviolet-enzymatic or a visible-colorimetric method. Chromatographic methods use high-pressure liquid chromatography (HPLC) with either a bonded-amine column, which is preferred, or an ion-exchange column.

In a recent survey conducted by the AOAC International Food and Nutrition Committee the FDA methodology appears to meet the definition criteria most frequently cited as appropriate by scientists working in the area of complex carbohydrates. However, a number of methodology issues still require resolution. Two basic issues concern completeness of starch digestion by the alpha-amylase-protease-amyloglucosidase mixture, and elimination of the long and tedious step of filtrate evaporation through implementation of newer, more sensitive HPLC detectors. Complex carbohydrate methodology must address quantification of oli-gosaccharides resistant to digestion in the human alimentary system. Finally, methodology implemented for determining complex carbohydrates requires multi-laboratory validation of its ruggedness, accuracy, and precision no matter how it is defined.

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