Determination of Insoluble, Soluble and Total Dietary Fiber in Foods using a Rapid Integrated Procedure of Enzymatic-Gravimetric-Liquid Chromatography: First Action 2022. 01.

BACKGROUND: A simple, accurate and reliable method for the measurement of total dietary fiber (TDF) according to the Codex definition (2009) was developed and successfully validated as AOAC Official Method of Analysis (OMA) 2017.16. Subsequently, OMA 2017.16 was modified to allow separate measurement of soluble and insoluble dietary fiber fractions.

OBJECTIVE: To perform a collaborative study to evaluate the repeatability and reproducibility of OMA 2017.16 modification for the measurement of TDF as insoluble dietary fiber (IDF) and soluble dietary fiber (SDF) measured as a) water soluble dietary fiber that precipitates in 78% aqueous ethanol (SDFP), and b) water soluble dietary fiber that remains soluble in 78% aqueous ethanol (SDFS) of degree of polymerization ≥3.

METHOD: Duplicate test portions are incubated with pancreatic α-amylase, amyloglucosidase, and protease under the conditions employed in OMA 2017.16. For the measurement of IDF, the digestate is filtered and the IDF determined gravimetrically. SDFP in the IDF filtrate is precipitated with alcohol and captured by filtration and determined. SDFS in the SDFP filtrate is recovered and quantitated by LC. The matrixes included cereal products and flours, vegetables, health food snacks, soup, chocolate and beans. Additional materials were analyzed by collaborators as "practice samples".

RESULTS: With the diethylene glycol internal standard, all MLV matrixes resulted in repeatability relative standard deviations (RSDr) for TDF analyses of < 3.60% and reproducibility relative standard deviations (RSDR) ranging from 4.55 to 9.26%. For the practice samples, the RSDR for TDF ranged from 6.69 to 11.68%.

CONCLUSIONS: OMA 2022.01 meets the AOAC requirements for repeatability and reproducibility and the data support First Action status.

HIGHLIGHTS: OMA 2022.01 is a robust and reproducible method for the analysis of insoluble, soluble (SDFP and SDFS) and total dietary fiber in a wide range of matrixes.