Overview
EN ISO 5377:1994 (ISO 5377:1981) specifies the Lane and Eynon constant‑titre titration method for measuring the reducing power and dextrose equivalent (DE) of starch hydrolysis products. The procedure uses a prescribed volume of mixed Fehling’s solution titrated against a test solution, with methylene blue as the internal indicator. An informative annex describes a paper‑chromatography check of standard reference anhydrous D‑glucose required for standardization.
Key topics and technical requirements
- Scope: Applicable to all starch hydrolysis products (glucose syrups, dextrose, maltodextrins) to determine reducing sugars and DE by titration.
- Reagents and solutions: Composition of Fehling stock solutions (CuSO4 solution and tartrate/NaOH solution) and preparation of the mixed Fehling’s solution immediately before use. Methylene blue (internal indicator) and anhydrous D‑glucose standard are required.
- Standardization: Mixed Fehling’s solution must be standardized daily against a D‑glucose standard; operators are advised to perform their own standardization titration.
- Titration procedure: Boiling test flask, timed heating, controlled addition of glucose or test solution in small increments until the methylene blue colour is discharged. Target titre range for standardization is 19.0–21.0 mL (operator‑specific).
- Sample preparation: Test portion prepared to make 500 mL test solution containing a specified amount of reducing sugars; dry matter (DMC) determination is required (referenced ISO methods for glucose syrup/dextrose).
- Calculations: Results expressed as reducing power (g anhydrous D‑glucose per 100 g sample) and dextrose equivalent (DE) (% of dry matter) calculated from titration volumes, test portion mass and dry matter content.
- Quality criteria: Repeatability (same analyst) limit ≈ 0.75% of mean; reproducibility (different labs) limit ≈ 1.5% of mean.
- Annex: Paper‑chromatography method for validating the anhydrous D‑glucose standard (detection of maltose/other sugars).
Applications and users
- Quality control laboratories in starch, syrup and sweetener production (glucose syrup, dextrose manufacturers)
- Food industry QC and R&D teams needing DE and reducing sugar data for formulation, labelling and process control
- Analytical chemistry laboratories performing regulatory or specification testing of starch‑derived products
- Suppliers and auditors verifying raw material conformity and standard reference solutions
Related standards
- ISO glassware and sampling standards referenced for burettes, pipettes and volumetric flasks (e.g., ISO 3851x series, ISO 648, ISO 1042) and ISO methods for dry matter determination of glucose/dextrose (ISO 1741, ISO 1742, ISO 1743).
Keywords: EN ISO 5377:1994, Lane and Eynon, reducing power, dextrose equivalent, starch hydrolysis products, Fehling’s solution, methylene blue, titration method, glucose syrup, anhydrous D‑glucose.
