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

    Paul Lawrance

    16 November 2009

  • LGC

    Established over 150 years ago

    UK government laboratory

    Privatised in 1996

    Acquisitions include: Promochem Group

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  • Group structure

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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- Ewers method

    Acid hydrolysis methods

    Enzymatic methods Hydrolysis of starch (& other -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 incr

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