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Collaborative Study Report: Determination of Insoluble, Soluble, and Total Dietary Fiber (Codex Definition) by an Enzymatic-Gravimetric Method and Liquid Chromatography B. V. McCleary (1), J. W. DeVries (2), J. I. Rader (3), G. Cohen (4), L. Prosky (5), D. C. Mugford (6), M. Champ (7), and K. Okuma (8). (1) Megazyme International, Bray, Co. Wicklow, Ireland. (2) Medallion Laboratories/General Mills, Golden Valley, MN, U.S.A. (3) U.S. Food and Drug Administration, College Park, MD, U.S.A. (4) Kraft Foods (retired), New City, NY, U.S.A. (5) U.S. Food and Drug Administration (retired), Rockville, MD, U.S.A. (6) BRI Australia Pty. Ltd., North Ryde, NSW, Australia. (7) UMR PhAN, INRA, CRNH, Nantes, Cedex 1, France. (8) Matsutani Chemical, Research Laboratory, Itami City, Japan. Cereal Foods World 56(6):238-247. A method for the determination of insoluble, soluble, and total dietary fiber (IDF, SDF, and TDF, respectively), as defined by the Codex Alimentarius Commission, was validated for foods. Based on the principles of AACC Intl. Approved Methods 32-05.01, 32-07.01, 32-41.01, and 32-40.01, the method quantitates water-insoluble and water-soluble dietary fiber. This method extends the capabilities of the previously adopted AACC Intl. Approved Method 32-45.01 (Total Dietary Fiber in Foods, Enzymatic–Gravimetric–Liquid Chromatographic Method). (This method is applicable to plant materials, foods, and food ingredients consistent with the 2009 Codex definition [ALINORM 09/32/REP], including naturally occurring, isolated, modified, and synthetic polymers meeting this definition.) In 2007, McCleary described a method of extended enzymatic digestion at 37°C designed to simulate human intestinal digestion followed by gravimetric isolation and quantitation of HMWDF (high molecular weight dietary fiber) and the use of liquid chromatography (LC) to quantitate LMWSDF (low molecular weight soluble dietary fiber). The use of the terms HMWDF and LMWSDF in this context is a bit misleading, because the method does not quantitate dietary fiber on the basis of molecular weight, but rather on the basis of solubility in a solution of one part water and four parts alcohol. Thus, HMWDF actually consists of dietary fiber that is insoluble or precipitates in the water-alcohol mixture, and LMWSDF is dietary fiber that remains soluble in the same mixture. The method reported here quantitates water-insoluble dietary fiber (IDF) separately from water-soluble dietary fiber (SDF). SDF includes the dietary fiber that precipitates (SDFP) in the presence of 78% aqueous ethanol or IMS (industrial methylated spirits) and dietary fiber that remains soluble (SDFS) in 78% aqueous ethanol (formerly termed LMWSDF). The method, thus, quantitates the complete range of water-insoluble and water-soluble fractions (by inclusion of the fractionation steps of AACC Intl. Approved Methods 32-20.01 and/or 32-07.01) of dietary fiber components from resistant starch (by utilizing the digestion conditions of AACC Intl. Approved Method 32-40.01) to digestion-resistant oligosaccharides (by incorporating deionization and LC procedures similar to those of AACC Intl. Approved Method 32-41.01). A further option for increased laboratory productivity using on-line, simultaneous deionization and LC quantitation has recently been published and has been incorporated as an option in the new method. The method was evaluated through an AACC International/AOAC International collaborative study. A total of 22 laboratories participated, with 19 laboratories returning valid assay data for 16 test portions (8 blind duplicates) consisting of samples with a range of traditional dietary fiber, resistant starch, and nondigestible oligosaccharides. The dietary fiber content of the eight test pairs ranged from 10.45 to 29.90%. Digestion of samples under the conditions of AACC Intl. Approved Method 32-40.01 followed by the isolation, fractionation, and gravimetric procedures of AACC Intl. Approved Methods 32-05.01and 32-07.01 resulted in quantitation of IDF and water-soluble but water-alcohol–insoluble dietary fiber (SDFP). The filtrate from the quantitation of SDFP was concentrated, deionized, concentrated again, and analyzed by LC to determine water-alcohol–soluble dietary fiber (SDFS), i.e., all dietary fiber polymers with DP >= 3, consisting primarily, but not exclusively, of oligosaccharides. SDF was calculated as the sum of SDFP and SDFS. TDF was calculated as the sum of IDF and SDF. For IDF the within laboratory variability (s(r)) ranged from 0.18 to 0.71, and the between laboratory variability (s(R)) ranged from 0.42 to 2.24. For SDF, s(r) ranged from 0.28 to 1.03, and s(R) ranged from 0.85 to 1.66. For TDF, s(r) ranged from 0.47 to 1.41, and s(R) ranged from 0.95 to 3.14. This is comparable to other official and approved dietary fiber methods. The study directors recommended this method be granted First Approval status by AACC International. Method 32.50.01 was approved in August 2011.
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