TOTAL DIETARY FIBER DETERMINED AS NEUTRAL SUGAR RESIDUES, URONIC-ACIDRESIDUES, AND KLASON LIGNIN (THE UPPSALA METHOD) - COLLABORATIVE STUDY

A joint AOAC/American Association of Cereal Chemists (AACC) collaborat ive study was conducted to determine by the Uppsala method the dietary fiber content and its composition in various foods. The method includ es preparation of a residue by treatment with thermostable alpha-amyla se and amyloglucosidase and then ethanol precipitation of solubilized dietary fiber components while leaving low-molecular weight carbohydra tes in solution. After acid hydrolysis of residue, neutral polysacchar ide residues are determined as alditol acetates by gas-liquid chromato graphy, uronic acid residues are determined by colorimetry, and ash-fr ee acid-insoluble residue (Klason lignin) is determined gravimetricall y. Total dietary fiber, including enzyme-resistant starch, is calculat ed as the sum of nonstarch polysaccharide residues and Klason lignin. Nine laboratories completed the study, analyzing in duplicate 8 unknow n dried products that included 4 cereal products, green peas, potato f iber, carrots, and apples. Total dietary fiber contents of products te sted ranged from 4.6 to 84.3%, with an average RSD(R) value of 8.4% (r ange, 4.8-11.1%). Total neutral polysaccharide residues ranged from 3. 8 to 64.1%, with an average RSD(R) value of 7.5% (range, 5.4-10.5%). I ndividual neutral sugars (rhamnose, arabinose, xylose, mannose, galact ose, and glucose) and uronic acid residues present at more than 1% gen erally had good RSD(R) values (3.3-22.8%), whereas, as expected for Kl ason lignin, only the wheat bran sample with a high content (16%) had an excellent RSD(R) value (5.0%). The gas chromatographic-colorimetric -gravimetric method (Uppsala method) for determination of total dietar y fiber (as neutral sugar residues, uronic acid residues, and Klason l ignin) has been adopted first action by AOAC INTERNATIONAL.