analysis of dietary fibre - centre for food · pdf fileanalysis of dietary fibre. 2 hk...
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Analysis of Dietary Fibre
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HK Regulation
Dietary fibre means any fibre analyzed by means of any official methods adopted by AOAC International.
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AOAC Official Methods
Enzymatic-Gravimetric MethodTotal Dietary Fibre (Applicable to determination of total fibre in cereals, beans, vegetables and fruits)
AOAC 992.16
etc
Enzymatic-Gravimetric MethodInsoluble Dietary Fibre in Foods and Food Products
AOAC 991.42
Enzymatic-Gravimetric MethodTotal, Soluble, and Insoluble Deitary Fibre in Foods
AOAC 991.43
Enzymatic-Gravimetric MethodTotal Dietary Fibre in FoodsAOAC 985.29
AOAC 993.19 Enzymatic-Gravimetric MethodSoluble Dietary Fibre in Food and Food Products
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AOAC 985.29
Duplicate test portions of
sample
Duplicate test portions of
sample
Enzymatic digestioni) α-amylaseii) proteaseiii) amyloglucosidase
Enzymatic digestioni) α-amylaseii) proteaseiii) amyloglucosidase
Total dietary fibre = weight (residue) – weight (ash + protein)Total dietary fibre = weight (residue) – weight (ash + protein)
Precipitation and filtration (residue)Precipitation and filtration (residue)
One residue for ash analysis
One residue for ash analysis
One residue for protein analysisOne residue for protein analysis
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AOAC 985.29
Homogenize and dry sample (freeze-dry is recommended).
Defat with petroleum ether if >10% fat content, otherwise false high results.
Weigh duplicate test portions (difference in weight should not >20 mg).
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AOAC 985.29Preparing for digestion
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AOAC 985.29Preparing for digestion
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AOAC 985.29α-Amylase: gelatinize
Add phosphate buffer (pH 6.0, 50 mL) to sample.
Adjust to pH 6.0 ± 0.2.
Add enzyme, incubate at 95 – 100 °C.
30 minutes in water bath.
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AOAC 985.29
Protease: remove protein
Cool to room temperature.
Adjust to pH 7.5 ± 0.2.
Add enzyme, incubate at 60 °C for 30 minutes.
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AOAC 985.29
Amyloglucosidase: remove starch
Cool.
Adjust to pH 4.0 – 4.6.
Add enzyme, incubate at 60 °C for 30 minutes.
Note: final solution volume is about 70 mL.
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AOAC 985.29Summary
pH 6.0 ± 0.2, α-amylase, 95 – 100 °C,15 - 30 min.
pH 7.5 ± 0.2, protease, 60 °C, 30 min.
pH 4.0 – 4.6, amyloglucosidase, 60 °C, 30 min.
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AOAC 985.29
Add 280 mL 95 % ethyl alcohol (60 oC).
Let precipitate form at room temperature for 60 minutes.
Collect the residues (soluble fibre + insoluble fibre) in pre-weight crucibles.
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AOAC 985.29Precipitation
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AOAC 985.29Filtration
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AOAC 985.29One test portion for protein, using N x 6.25 as conversion factor.
Incinerate second test portion at 525 oC for5 hours.Total dietary fibre = [weight residue – protein –
ash – blank] / weight test portion
Weight residue = average of duplicateWeight test portion = average of duplicate
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AOAC 985.29Test for enzyme purity every half yearly
95-1000.1β-Glucanaseβ-Glucan (barley gum)
0-20.3ProteaseCasein
0-21.0AmylaseCorn Starch
0-11.0AmylaseWheat Starch
95-1000.1HemicellulaseStractan (larch gum)
95-1000.1PectinaseCitrus pectin
Expected recovery (%)
Test portion (g)Activity testedTest sample
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AOAC Method for functional fibre
AOAC 2002.02C*ActistarResistant starch
AOAC 2001.03Fibersol-2Resistant maltodextrin
AOAC 2001.02Yacult, Borculo Whey ProductsGalactooligosaccharides
AOAC 2000.11Litesse®Polydextrose
AOAC 997.08 or 999.03Neosugar, Actilght®Fructooligosaccharides
AOAC 997.08 or 999.03 Raftilose®, OliggoFiberTMOligofructose
AOAC 995.16Imprime PGG®Beta-glucan
Test MethodCommercial nameFunctional fibre
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AOAC 2001.03
Dietary Fiber Containing Supplemented Resistant Maltodextrin (RMD)
High MW RMD by Method 985.29 andLow MW RMD by HPLC
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AOAC 2001.03
Filtrate (by 985.29)
Filtrate (by 985.29)
i) Concentrateii) Desalti) Concentrateii) Desalt
Total dietary fibre = [weight of residue -protein – ash - blank] + [weight of low MW soluble fibre determined by HPLC]
Total dietary fibre = [weight of residue -protein – ash - blank] + [weight of low MW soluble fibre determined by HPLC]
Analysed by LCAnalysed by LC
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AOAC 2001.03
Only a portion of the resistant maltodextrin is precipitated in the aqueous ethanol when Method 985.29 is applied to foods containing resistant maltodextrin.
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AOAC 2001.03
In Method 2001.03, resistant maltodextrin that are soluble in aqueous ethanol are desalted, concentrated and measured by liquid chromatography.
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Desalting
Ion exchange column(OH-type and H-type)
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AOAC 2001.03
Total dietary fibre =fibre as measured by Method 985.29 plus low molecular weight resistant maltodextrin
Note: low molecular weight resistant maltodextrin refers to resistant maltodextrin that are soluble in the aqueous ethanol in Method 985.29.
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Calculation of available carbohydrate when method 2001.03 is used
Available carbohydrate = 100 – [moisture + ash + protein + fat + alcohol + (soluble dietary fibre + insoluble dietary fibre) + low molecular weight resistant maltodextrin]
Note: low molecular weight resistant maltodextrin refers to resistant maltodextrin that is measured by AOAC 2001.03.
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Recoveries for other functional fibreswhen tested by AOAC 2001.03
88Resistant maltodextrin
46Glucooligosaccharides
117Polydextrose
111Galactooligosaccharides
101*β-Glucan
98Fructooligosaccharides
Recovery (%)Functional fibre
* * Recovery of insoluble dietary Recovery of insoluble dietary fibrefibre and soluble dietary and soluble dietary fibrefibre is particular high.is particular high.
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Points to note
Definition of “0”: ≤1 g/100 g.Results are method dependent.
Functional fibre should be included in the calculation of available carbohydrate.
AOAC 2001.03 may give higher TDF results but with higher testing cost.
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Available proficiency test
FAPAS
AOAC
LGC
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Thank You