Submitted to: Journal of Association of Official Analytical Chemists International
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 18, 1995
Publication Date: N/A
Interpretive Summary: With the passage of the Nutrition Labeling and Education Act of 1990 and the proposal by FDA in the Federal Register, food carbohydrates; namely sugars and dietary fiber are now considered mandatory nutrients for nutrition labeling. Improved methods of analysis for the five common food sugars, have been developed using either gas-liquid chromatography (GLC) or high-performance liquid chromatography (HPLC). Unlike the sugars, dietary fiber are usually determined gravimetrically as a mixture consisting of non-starch polysaccharides, lignin, and other associated material insoluble in dilute alcohol. Since early 1980s,our laboratory has been evaluating and developing methods for sugars, starches, and dietary fiber analysis. Recently we integrated the procedures for the independent determination of food carbohydrates, and were able to analyze half a gram of a dry sample sequentially for the vaious fractions. Our objective is to validate the method by analyzing portions of selected high consumption foods that have been analyzed by a commercial laboratory for sugars and dietary fiber. Results indicated that total sugar and dietary fiber values method are comparable between laboratories using different methods. There has been very little available data on starch content of foods in general, The data we are presenting here should be useful to nutritionists, epidemiologists, and health professionals.
Technical Abstract: A general scheme has been developed to determine sugars, starches and total dietary fiber (TDF) in a 0.5 g freeze dried food sample. Free sugars are extracted into 80% methanol, dried and derivatized to their trimethysilylated oximes or ethers, and quantitated on a gas-liquid chromatograph (GLC). The residues after the dilute alcohol extraction are suspended in deionized water, autoclaved at 120 deg. C for 1 h, cooled to 60 deg. C, mixed with a solution containing amyloglucosidase in acetate buffer. The mixtures are incubated at 55 deg. C for 2 h. The hydrolyzates are centrifuged and duplicate aliquots (0.1 mL) 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 4 x volume of 95% ethanol, and the mixtures are left at room temperature for l h, then filtered through glass crucibles matted with celite filter aid. The residues are dried at 100 deg. C for at least 2 h, and cooled in the desiccator. One of the pair of residues is analyzed for crude protein and the other for ash. TDF content is calculated as the residue weight corrected for crude protein and ash. A variety of high consumption foods were analyzed for the various carbohydrate fractions using the method described above. Values for total sugar and dietary fiber from this study are compared with those obtained by a commercial laboratory using different methods.