Collaborative study report: determination of insoluble, soluble, and total dietary fiber (Codex definition) by an enzymatic-gravimetric method and liquid chromatography.

摘要

A method for the determination of soluble, insoluble and total dietary fibre (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 32-40.1, the method quantitates water-insoluble and water-soluble dietary fibre. This method extends the capabilities of the previously adopted AACC Intl. Approved Method 32-45.01 (Total Dietary Fiber in Foods, Enzymatic-Gravimetric-Liquid Chromatography Method). In 2007, a method was described that included extended enzymic digestion at 37 degrees C, designed to simulate human intestinal digestion, followed by gravimetric isolation and quantitation of high mol. wt. dietary fibre (HMWDF) and the use of LC to quantitate low mol. wt. soluble dietary fibre (LMWSDF). Use of the terms HMWDF and LMWSDF in this context may be misleading because the method does not quantitate dietary fibre on the basis of mol. wt., but rather on the basis of solubility in a solution of 1 part water and 4 parts alcohol. Thus, HMWDF actually consists of dietary fibre that is insoluble or precipitates in the water-alcohol mixture and LMWSDF is dietary fibre that remains soluble in the same mixture. The method reported here quantitates water-insoluble dietary fibre (IDF) separately from water-soluble dietary fibre (SDF). SDF includes the dietary fibre that precipitates (SDFP) in the presence of 78% aqueous ethanol or industrial methylated spirits (IMS) and dietary fibre 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 of dietary fibre components from resistant starch to digestion-resistant oligosaccharides. A further option for increased laboratory productivity using on-line, simultaneous deionization and LC quantitation was incorporated as an option in this 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 fibre, resistant starch and nondigestible oligosaccharides. The dietary fibre content of the 8 test pairs ranged from 10.45 to 29.90%. Digestion of samples under the conditions of AACC Intl. Approved Method 32-10.01 followed by the isolation, fractionation and gravimetric procedures of AACC Intl. Approved Methods 32-05.01 and 32-07.01 resulted in quantitation of IDF and water-soluble but water-alcohol-insoluble dietary fibre (SDFP). Filtrate from the quantitation of SDFP was concentrated, deionized, concentrated again and analysed by LC to determine water-alcohol soluble dietary fibre (SDFS), i.e., all dietary fibre 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, within laboratory variability (s_r) ranged from 0.18 to 0.71, and 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 was comparable to other official and approved dietary fibre methods. It was recommended that this method be granted First Approval status by AACC International, and method 32.50.01 was approved in Aug. 2011.