GIFSQ Tools · Module 1 — Food Composition & Proximate Analysis · Tool 10 of 500
Enzymes digest the starch and protein, ethanol drops the soluble fibre out, and what is left on the filter is the fibre — once you subtract the protein, ash and blank. Enter the residue and its corrections.
Try sample values — fills the form with the worked example below.
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Total dietary fibre (%)
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Corrected residue (g)
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Fibre %, dry basis
Equation: Total dietary fibre % = (mresidue − mprotein − mash − mblank) ÷ msample × 100
Dry basis: Fibre % (dry) = Fibre % ÷ (dry matter % ÷ 100).
Method: Enzymatic-gravimetric, AOAC 985.29 — heat-stable α-amylase, protease and amyloglucosidase digest the starch and protein, 95 % ethanol precipitates the soluble fibre, the residue is filtered, dried and weighed, then corrected for its protein (Kjeldahl) and ash, minus the blank. AOAC 991.43 runs the same steps with the soluble and insoluble fractions filtered separately: total dietary fibre = insoluble + soluble.
Assumptions: the enzymes fully digest starch and protein; ethanol precipitates all soluble fibre; the blank captures the residue the reagents alone leave behind.
Limitations: resistant starch and some soluble fibres are partly lost; the method does not say which fibre types are present; low-molecular-weight soluble fibre (inulin, fructo-oligosaccharides) is missed — AOAC 2009.01 / 2011.25 covers it. Crude fibre (Tool 9) is a different, smaller number for the same food — never compare the two directly.
Rounding: results to 2 decimal places; intermediate values are not rounded.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Dry basis: Fibre % (dry) = Fibre % ÷ (dry matter % ÷ 100).
Method: Enzymatic-gravimetric, AOAC 985.29 — heat-stable α-amylase, protease and amyloglucosidase digest the starch and protein, 95 % ethanol precipitates the soluble fibre, the residue is filtered, dried and weighed, then corrected for its protein (Kjeldahl) and ash, minus the blank. AOAC 991.43 runs the same steps with the soluble and insoluble fractions filtered separately: total dietary fibre = insoluble + soluble.
Assumptions: the enzymes fully digest starch and protein; ethanol precipitates all soluble fibre; the blank captures the residue the reagents alone leave behind.
Limitations: resistant starch and some soluble fibres are partly lost; the method does not say which fibre types are present; low-molecular-weight soluble fibre (inulin, fructo-oligosaccharides) is missed — AOAC 2009.01 / 2011.25 covers it. Crude fibre (Tool 9) is a different, smaller number for the same food — never compare the two directly.
Rounding: results to 2 decimal places; intermediate values are not rounded.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Worked example: sample 1.000 g, residue 0.350 g, protein in residue 0.015 g, ash in residue 0.010 g, blank 0.005 g. Corrected residue = 0.350 − 0.015 − 0.010 − 0.005 = 0.320 g; total dietary fibre = 0.320 ÷ 1.000 × 100 = 32.00 %. With dry matter 90.00 %, fibre on a dry basis = 32.00 ÷ 0.90 = 35.56 %.
Enter values above to see results.
Typical total dietary fibre: white bread 2–3 %, whole wheat bread 6–7 %, oats 10–11 %, wheat bran 40–45 %, lentils 30–31 %. Always state the method with the number — AOAC 985.29 and AOAC 991.43 do not give identical results. Tool 10 of 500 — GIFSQ
