Author
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Li, Betty |
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Submitted to: New Techniques in the Analysis of Food
Publication Type: Proceedings Publication Acceptance Date: 1/1/1998 Publication Date: N/A Citation: N/A Interpretive Summary: A method has been developed and modified in this laboratory for the determination of free sugars, starches, and dietary fiber polysaccharides (DFP) starting with half a gram of a dry food sample. The procedures consist of extracting free sugars into dilute methyl alcohol, hydrolyzing starches to glucose, and isolating dietary fiber residues, which are hydrolyzed with sulfuric acid to yield a mixture of neutral sugars. The various sugar mixtures in different carbohydrate fractions are separated and quantified on the same high performance anion exchange chromatographic column with pulsed amperometric detection(HPAE-PAD)using slightly different chromatographic conditions. Good correlations were found between the total sugar, starch, and DFP contents of 5 selected test samples using HPAEC-PAD method and a gas-liquid chromatography-flame ionization detection method (from an earlier study). We have shown the practicality of determining sugars, starches, and DFP from the same half gram subsample of a freeze dried food using a simplified fractionation scheme and the same High Performance Liquid Chromatographic column for the quantification of different mixtures of sugars. This method should be useful for all analysts interested in food carbohydrates. Data that will be generated using this method are much needed by nutritionists, health professionals, and consumers. Technical Abstract: Carbohydrates, as a class of macronutrient, have been for many years, calculated by difference in proximate analysis. During the past two decades, chromatographic separations of food sugars in their free form or as hydrolysis products of their polymers have become more prevalent using gas-liquid chromatography (GLC) or high-performance liquid chromatography HPLC). With sequential solvent extractions, enzyme hydrolysis and mineral acid hydrolysis, sugar, starch, and dietary fiber polysaccharide contents can now be determined in the same half-gram subsample of a variety of foods. Sugars (mono-and disaccharides) are extracted into 80% methanol, starches are hydrolyzed to glucose by amyloglucosidase in acetate buffer, and dilute alcohol insoluble materials are isolated as dietary fiber residues, which are hydrolyzed in sulfuric acid to yield a mixture of monosaccharides. Individual sugars in different fractions can be quantified as specific derivatives on GLC. Recently, high performance anion exchange chromatography coupled with pulsed amperometric detection (HPAEC-PAD) has been used for determining the same sugars in aqueous solution without further derivatization. |
