ISO 5377:1981

Overview

ISO 5377:1981 is an international standard developed by the International Organization for Standardization (ISO) that outlines the Lane and Eynon constant titre method for the determination of reducing power and dextrose equivalent in starch hydrolysis products. This standard specifies a titration procedure using mixed Fehling’s solution and methylene blue as an internal indicator to accurately quantify the amount of reducing sugars, expressed as anhydrous D-glucose, in various starch-derived substances.

This method is critical for researchers, quality control laboratories, and industries working with starch derivatives, glucose syrups, and related products, providing a reliable assessment of their reducing sugar content and dextrose equivalence, which are essential parameters in food, fermentation, and chemical manufacturing processes.

Key Topics

• Scope and Application
  ISO 5377 applies to all starch hydrolysis products and defines a standardized procedure for titrating a test solution with Fehling’s reagent to measure the reducing sugar content.

• Principle of Method
  The key analytical technique involves titrating Fehling’s solution volume against a known volume of a test solution until the methylene blue indicator color disappears, signaling the endpoint. This reaction quantifies the reducing power, reflecting the concentration of reducing sugars.

• Reagents and Apparatus

  • Fehling's stock solutions (Copper sulfate, potassium sodium tartrate, sodium hydroxide)
  • Mixed Fehling’s solution prepared fresh prior to use
  • Methylene blue indicator for titration endpoint detection
  • Standard reference anhydrous D-glucose solution for calibration
  • Laboratory glassware compliant with ISO requirements for volumetric accuracy

• Test Procedure

  • Preparation of test sample and solutions
  • Standardization of Fehling’s solution against a glucose standard
  • Precise titration of the sample solution, controlling boiling conditions and increment additions
  • Calculation of reducing power and dextrose equivalent based on titration volumes and sample mass

• Expression of Results

  • Reducing power expressed as grams of anhydrous D-glucose per 100 g of sample
  • Dextrose equivalent expressed relative to dry matter content
  • Repeatability and reproducibility criteria to ensure data accuracy and reliability

• Informative Annex: Quality Control for D-Glucose Standard
  This annex provides a method to verify the quality of the anhydrous D-glucose reference standard, ensuring compliance with purity requirements using paper chromatography to detect impurities such as maltose and other sugars.

Applications

ISO 5377:1981 is principally utilized in industries and laboratories tasked with:

• Food and Beverage Industry
  Determining sugar content in glucose syrups, sweeteners, and starch hydrolysates to ensure product consistency and regulatory compliance.

• Starch Processing and Derivatives Manufacturing
  Monitoring enzymatic hydrolysis results and optimizing production processes based on accurate measurements of reducing sugars.

• Fermentation and Biotechnology
  Assessing fermentable sugar content in substrates to optimize microbial growth and product yields.

• Quality Control Laboratories
  Routine testing of raw materials and finished products to verify labeling claims related to sugar content and to detect adulteration.

• Research and Development
  Studying hydrolysis reactions and evaluating new starch derivatives or enzymatic treatments for improved functionality.

The use of the standard method ensures international comparability of results, facilitates trade, and supports regulatory frameworks governing food and chemical products.

Related Standards

ISO 5377 references and complements several related ISO standards to ensure consistent laboratory practice and result interpretation, including:

• ISO 3851, ISO 38512, ISO 648, ISO 1042, ISO 1773: Standards specifying requirements for laboratory glassware - burettes, pipettes, volumetric flasks, and boiling flasks, ensuring precise measurement and reproducibility.
• ISO 1741, ISO 1742, ISO 1743: Methods for determining dry matter content and loss on drying of glucose or glucose syrups, critical for calculating dextrose equivalents.
• ISO 5809: Specific methods for determining sulfated ash content in starch and derivatives.
• ISO 3851 (Draft): Laboratory glassware standards currently under revision, aiming to enhance volumetric accuracy further.

Together, these standards establish a robust framework for starch and glucose analysis, supporting the effectiveness and reliability of titrimetric methods like the Lane and Eynon procedure described in ISO 5377.

Keywords: ISO 5377, starch hydrolysis products, dextrose equivalent, reducing power, Lane and Eynon method, Fehling’s solution titration, methylene blue indicator, starch derivatives, glucose syrup testing, quality control, reducing sugars determination, international standard.