185 Measurement of Total Dietary Fibre in Cereals, Ingredients and Food Products Using the Rapid Integrated TDF Procedure (RINTDF)

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Methods Type: Generic Methods
Key data
Number: 185
Analyte: Total Dietary Fibre
Matrix: Cereals, Ingredients and Food Products
Year of Approval as Draft: 2017
Year of Approval as Regular Standard: 2019
 
Scope and field of application:

This method is an update of AOAC Method 2009.01 (also published as AACC Method 32-45.01) for the determination of total dietary fiber in foods and food ingredients as defined by the Codex Alimentarius Commission. Enzymatic digestion with pancreatic a-amylase (PAA) plus amyloglucosidase (AMG) at 37°C for 4 h is used to simulate human intestinal digestion. Higher molecular weight dietary fiber (HMWDF), including insoluble dietary fiber (IDF) and fiber which precipitates in the presence of 78% ethanol (SDFP) is measured gravimetrically. Resistant starch (RS) is captured in the IDF fraction. Dietary fiber that is soluble in 78% aqueous ethanol (SDFS) is recovered and measured by high-performance liquid chromatography (HPLC). Total dietary fibere is the sum of HMWDF (IDF plus SDFP) and SDFS.  The method measures the complete range of dietary fiber components from RS to digestion-resistant oligosaccharides (SDFS). Reducing the  incubation with PAA plus AMG from 16 h to 4 h makes the assay more physiologically relevant, resulting in more accurate measurement of RS, including RS2 and RS4, and complete hydrolysis of non-resistant starch and starch derived oligosaccharides. In this update of AOAC Method 2009.01, sodium azide is removed from buffers; desalting of samples for HPLC is simplified; accurate measurement of fructo-oligosaccharides and all other oligosaccharides is achieved using TSKgel® G2500PWXL  HPLC columns (in place of the Waters Sugar-Pak® column); and glycerol is employed as the internal standard in place of D-sorbitol (which occurs in some food products).

References:

- ICC Standard No 101/1, Sampling of grains.

- ICC Standard No. 110/1, Determination of moisture content of cereals and cereal products (practical method).

- ICC Standard No 130, Sampling of milling products (Semolina, flours, agglomerated flours and by-products)

- ICC Standard No 138, Mechanical sampling of milled cereal products

- ISO 24333, Cereal and Cereal products—sampling.

- ISO 3696, Water for analytical laboratory use-Specification and test methods.

Definition:

Based on the recommendation for endorsement of the Codex Committee on Nutrition and Foods for Special Dietary Uses (CCNFSDU) in November 2008, a definition for dietary fiber was adopted in June 2009 by the Codex Alimentarius Commission (CAC), as follows:

“Dietary fiber consists of carbohydrate polymers (a) with ten or more monomeric units (b), which are not hydrolysed by the endogenous enzymes in the small intestine of humans and belong to the following categories: edible carbohydrate polymers naturally occurring in the food as consumed; carbohydrate polymers which have been obtained from food raw material by physical, enzymatic or chemical means and which have been shown to have a physiological effect of benefit to health as demonstrated by generally accepted scientific evidence to competent authorities, and synthetic carbohydrate polymers which have been shown to have a physiological effect of benefit to health as demonstrated by generally accepted scientific evidence to competent authorities.

 a) When derived from a plant origin, dietary fiber may include fractions of lignin and/or other compounds when associated with polysaccharides in the plant cell walls and if these compounds are quantified by the AOAC gravimetric analytical method for dietary fiber analysis: Fractions of lignin and the other compounds (proteic fractions, phenolic compounds, waxes, saponins, phytates, cutin, phytosterols, etc.) intimately “associated” with plant polysaccharides (are often extracted with the polysaccharides) in the AOAC 991.43 method.

b)  Decision on whether to include carbohydrates of 3 to 9 monomeric units should be left up to national authorities.”

 

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