GIFSQ Tools · Module 2 — Food Chemistry & Physicochemical Testing · Tool 25 of 500
Lane-Eynon titration: titrate the sample solution against boiling Fehling’s solution and get the reducing sugar as invert sugar, in percent. AOAC 923.09.
Try sample values — fills the form with the worked example below.
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Reducing sugar (%)
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Titre (mL)
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Fehling factor (mg)
Equation: Reducing sugar % = F × V ÷ (T × m × 10), where F is the Fehling factor in mg of invert sugar per 10 mL of Fehling’s solution, V the dilution volume in mL, T the titre in mL, and m the sample weight in g.
Method: AOAC 923.09, Lane-Eynon general volumetric method — the sample solution is titrated against 10 mL of boiling Fehling’s solution (5 mL A + 5 mL B) to the methylene blue end point. The factor depends on the titre: AOAC Table 19 gives 50.5 mg at a 15 mL titre and 51.1 mg at a 25 mL titre, for invert sugar with no sucrose present. The default 51.1 mg suits a titre near 25 mL — enter the table factor for your own titre.
Assumptions: the Fehling’s solution is standardised; the end point is the disappearance of the blue colour; no other reducing substances are present.
Limitations: the titre must fall between 15 and 50 mL — outside that range the factor is not valid and the sample must be re-diluted. Sucrose does not reduce Fehling’s solution and is not counted here (see Tool 26).
Rounding: reducing sugar to 2 decimal places; titre and factor to 1 decimal place.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Method: AOAC 923.09, Lane-Eynon general volumetric method — the sample solution is titrated against 10 mL of boiling Fehling’s solution (5 mL A + 5 mL B) to the methylene blue end point. The factor depends on the titre: AOAC Table 19 gives 50.5 mg at a 15 mL titre and 51.1 mg at a 25 mL titre, for invert sugar with no sucrose present. The default 51.1 mg suits a titre near 25 mL — enter the table factor for your own titre.
Assumptions: the Fehling’s solution is standardised; the end point is the disappearance of the blue colour; no other reducing substances are present.
Limitations: the titre must fall between 15 and 50 mL — outside that range the factor is not valid and the sample must be re-diluted. Sucrose does not reduce Fehling’s solution and is not counted here (see Tool 26).
Rounding: reducing sugar to 2 decimal places; titre and factor to 1 decimal place.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Worked example: 5.000 g of jam made up to 250 mL; 25.0 mL of the solution reduces 10 mL of Fehling’s solution; factor 51.1 mg. Reducing sugar = 51.1 × 250 ÷ (25.0 × 5.000 × 10) = 10.22 % as invert sugar.
Enter values above to see results.
Typical reducing sugar: honey 60–75 %, jam 25–40 %, fruit juice 5–10 %, table sugar under 0.1 %. Keep the titration under 3 minutes at a full boil — a slow titration over-reduces and reads high. Tool 25 of 500 — GIFSQ
