ENZYMATIC CHEMICAL-ANALYSIS OF DIETARY FIBER

The Uppsala methodology for rapid analysis and characterization of tot al dietary fiber, defined as the sum of dietary fiber polysaccharides (DFP) and Klason lignin, was studied. A sugar- and starch-free residue was prepared by treatment with a thermostable amylase and amyloglucos idase. Neutral DFP residues were quantified by gas chromatography as a lditol acetates after acid hydrolysis of this residue, and the acid-in soluble fraction, Klason lignin, was determined gravimetrically. Uroni c acid residues were quantified by decarboxylation of the original sam ple. The efficacy of the Uppsala methodology was tested with foods var ying in fiber content and composition, including heat-treated samples. The present method allowed the analysis of up to 40 samples per week. It had good repeatability and coefficients of variation of 3-5% for t he main fiber components. Fiber contents determined with the method we re higher than those determined with a similar method that excludes Kl ason lignin and starch resistant to amylases but soluble in dimethyl s ulfoxide and lower than those determined with an enzymatic/gravimetric method. Important aspects of fiber analysis, like enzyme purity and t he recovery of soluble fiber on ethanol precipitation, also were inves tigated.