Scope and field of application

This method is a modification of ICC method 185 (AOAC Official Method of Analysis (OMA) 2017.16) that allows measurement of insoluble, soluble and total dietary fiber in plant material, foods and food ingredients. The definition of dietary fiber adopted by the Codex Alimentarius Commission (CAC) in June 2009 (CODEX, 2009) includes carbohydrate polymers that are not hydrolysed by the endogenous enzymes in the human small intestine, including resistant starch (RS) as well as non-digestible oligosaccharides (where allowed by national authorities). To meet the needs of this definition, a method was developed (McCleary, 2007) and validated as AOAC Method 2009.01 (and 2011.25) (McCleary et al., 2010; McCleary et al., 2011; AOAC INTERNATIONAL, 2016) and AACC Method 32-45.01 and 32-50.01 (McCleary et al., 2012; McCleary et al., 2015). Subsequently, limitations of this method were identified, including the time of incubation with pancreatic α-amylase (PAA) plus amyloglucosidase (AMG) (16 h) (Szarka & Camilleri, 2012; McCleary et al., 2015) not being physiologically relevant; excessive hydrolysis and thus underestimation of phosphate cross-linked starch (RS4); production of resistant oligosaccharides (Brunt & Sanders, 2013; McCleary et al., 2013) from non-resistant starch, underestimation of fructo-oligosaccharides (FOS) (McCleary, 2019) and the use of sodium azide (a toxic chemical) as a preservative. This led to the development of an improved method for measurement of total dietary fiber (TDF) in which all identified limitations were addressed, namely, the rapid integrated total dietary fiber method (RINTDF)(McCleary et al., 2015), which was successfully validated in an AOAC/AACCI/ICC multi-laboratory study, to become AOAC Official Method of Analysis (OMA) 2017.16 (McCleary et al., 2018), AACCI Recommended method 32-60.01 (AACC, 2010) and ICC method 185.

ICC Method 185/AOAC Method 2017.16 was then modified (according to the steps described in AOAC Method 2011.25) to allow the measurement of insoluble dietary fiber (IDF) and soluble dietary fiber (SDF) [as soluble dietary fiber that precipitates in 78% aqueous ethanol (SDFP) plus soluble dietary fiber that remains soluble in 78% aqueous ethanol (SDFS)] and TDF. In the study described here, this modified method has been subjected to interlaboratory validation under the auspices of AOAC INTERNATIONAL.

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 milled 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

Definitions

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.