FSA – An evaluation of the methodological approaches for the determination of different carbohydrate fractions in foods

Paul Lawrance

16 November 2009

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An evaluation of the methodological approaches for the determination of different carbohydrate fractions in foods.

Food Standards Agency 2009.

• Aim

To review and evaluate options available to analysts determining the various carbohydrate fractions that occur naturally and that have been added to foods.

What are carbohydrates?

• Sugars: glucose, fructose, sucrose, maltose, galactose

• Starch: Various types, resistant starch, modified starch

• Partially hydrolysed starch products : Maltodextrins, glucose syrups,

fructose syrups

• Other oligosaccharides: FOS, GOS, XOS, Polydextrose etc

• Dietary fibre: NSP, cellulose, hemi-cellulose, pectins, gums and

mucilages, algal polysaccharides, lignin

Confusing terms

• Carbohydrates: Available, non-available, glyceamic, non-glyceamic

• Sugars, reducing sugars, non-reducing sugars, total sugars, free sugars, added sugars, refined sugars, extrinsic sugars, intrinsic sugars, milk sugars, monosaccharides, disaccharides, oligosaccharides……

• Partially hydrolysed starch, maltodextrin, glucose syrup, fructose syrup….

• Starch, slowly digestible starch, rapidly digestible starch, resistant starch, modified starch, polysaccharides....

• Dietary fibre, Non-starch polysaccharides (NSP), insoluble fibre, soluble fibre, cellulose, hemicellulose, … No agreed definition.

Carbohydrates by difference

• %Carbohydrate =

100% - %protein - %fat - %moisture - %minerals

• Non-specific

• No information about different carbohydrate types

• Subject to uncertainty in the other determinations.

• Specific methods preferred.

Methods for sugars

• Physical methods:

– Polarimetry, refractometry

• Chemical methods:

– Gravimetry: e.g.Munson & Walker (Total reducing sugars)

– Titration: e.g. Lane & Eynon (Total reducing sugars)

– Colorimetry: Anthrone method, Phenol-sulphuric (reducing and non-reducing

sugars)

– Enzymatic Assays (e.g. hexakinase / glucose oxidase for glucose)

• Instrumental methods

– HPLC, GLC, HPAEC,

Methods for starch

• Physical and chemical methods– Iodine titration, polarimetry- Ewer’s method

• Acid hydrolysis methods

• Enzymatic methods– Hydrolysis of starch (& other α-glucans) with amylase and

amyloglucosidase to form glucose.

– AOAC, AACC, Englyst, Megazyme, Other

– Modified starch

– Resistant starch

Methods for fibre

• Many methods proposed in the last two decades:

• Crude fibre, acid detergent fibre, neutral detergent fibre, Uppsala method, Theander method, AOAC methods, Englyst (NSP) methods.

• AOAC (985.29, 991.43) most commonly used

• Englyst (NSP) in UK for claims but AOAC also used for labelling.

• Newer methods for resistant starch, oligosaccharides,

polydextrose, resistant maltodextrins, fructans

Codex definition of dietary fibre

Dietary fibre means carbohydrate polymers1 with ten or more monomeric units 2, which are not hydrolysedby 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,

• 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.

Methods of Analysis for Dietary Fibre→ To be agreed.

1 When derived from a plant origin, dietary fibre 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 fibre 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. These substances are included in the definition of fibre insofar as they are actually associated with the poly- or oligo-saccharidic fraction of fibre. However, when extracted or even re-introduced into a food containing non digestible polysaccharides, they cannot be defined as dietary fibre. When combined with polysaccharides, these associated substances may provide additional beneficial effects (pending adoption of Section on Methods of Analysis and Sampling).

2 Decision on whether to include carbohydrates from 3 to 9 monomeric units should be left to national authorities.

EC definition (Directive 2008/100/EEC) includes carbohydrates with >3 monomeric units with similar categories and includes the concepts of indigestibility and physiological effect.

Background to the project

• For nutrition labelling, claims and enforcement purposes, there is a need to accurately quantify the presence of a range of carbohydrate components in foods.

• Information should be of nutritional relevance, should assist consumers with informed dietary selection and should not be open to misinterpretation.

• A large number of AOAC and other methods for the determination of various fractions of starch, oligosaccharides and dietary fibre are available.

• Industry and enforcement analysts face difficult analytical choices if they wish to produce data that will withstand critical review.

• Increasing knowledge of the physiological effects of carbohydrate components, the complexity of carbohydrate products commercially available and the ever increasing consumer and marketing interest in this area requires more complex analytical methods and a greater understanding of what is being determined.

• There is a need to evaluate the rationale, specificity, accuracy and reproducibility of individual, as well as combinations of methods, to ensure that reliable and defendable food composition information can be derived by analysts.

Problems of combining methods

FSA Project –Evaluation of methods for carbohydrates in food

• Objective 1 Method review and evaluation

– Review information on methods used for the determination of carbohydrate fractions

– Review information on innovative carbohydrates available for food supplementation with respect to foods and food supplements

• Objective 2 Selection and preparation of test ingredients and foods

– Preparation of model food substrates

– Identification of carbohydrate ingredients

Objective 3

• Evaluation of methods (particularly for dietary fibre)

• Direct chemical approach – FSA project E01078 by Englyst Carbohydrates

• Empirical approach – (AOAC 991.43 etc)

• New AOAC method for Total dietary fibre according to McCleary 2007 (AOAC 2009.01)

• Specific methodology issues

• Polyols

• Maltodextrins

• Starch

• Resistant starch

• Resistant short chain carbohydrates

Objective 4

• Effect of food processing and sample preparation on RS determination.

• Investigate the effect of food and sample preparation on RS content

• Dissemination of results relating to RS determination

Objective 5

• NSP constituent sugar profiling

• Development of a system utilising NSP constituent sugar profiles as a forensic tool to identify and/or authenticate the presence of added polysaccharide extracts

Objective 6

• Production of a guidance document for carbohydrate determination

• Prepare guidance document summarising the findings of the project

• Carbohydrate analysis workshop – end 2010.

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