ISO 5547:2008

Overview

ISO 5547:2008 | IDF 91:2008 is an internationally recognized reference method for determining the free acidity of caseins. Developed jointly by the International Organization for Standardization (ISO) and the International Dairy Federation (IDF), this standard specifies a precise laboratory procedure for measuring free acidity in caseins derived from acid precipitation, lactic fermentation, or rennet coagulation. Accurate determination of free acidity is critical for quality control and characterization of casein products used extensively in the dairy industry.

This standard is essential for laboratories and dairy manufacturers who require consistent and repeatable analytical results for the acidity profile of casein powders and related products.

Key Topics

• Scope and Application
  ISO 5547:2008 applies specifically to caseins obtained by acid precipitation, lactic fermentation, or rennet caseins. It defines a standard titrimetric method using sodium hydroxide and phenolphthalein indicator for quantifying free acidity expressed as millilitres of 0.1 mol/l NaOH required for neutralization.

• Method Principle
  The method involves extracting casein at 60 °C using distilled water, filtering, and titrating the aqueous extract with standardized sodium hydroxide while monitoring the endpoint with phenolphthalein.

• Sampling and Sample Preparation
  A representative, well-mixed laboratory sample must be prepared. Samples are sieved or ground to pass through a 500 µm test sieve to ensure homogeneity and avoid moisture changes during handling.

• Reagents and Apparatus
  Use of analytical grade reagents including a standard 0.1 mol/l sodium hydroxide solution and phenolphthalein indicator is required. Specified laboratory glassware such as burettes, pipettes, and measuring cylinders compliant with ISO standards ensure measurement accuracy.

• Calculation and Reporting
  The free acidity is calculated by the volume of sodium hydroxide used, adjusted for sample mass and solution concentration. Results are reported to the nearest 0.1 ml sodium hydroxide per gram of product, with options to express acidity on a dry basis considering moisture content measured by a referenced standard (ISO 5550).

• Precision and Repeatability
  The standard defines acceptable limits for repeatability (within 0.02 ml NaOH per 1 g) and reproducibility (within 0.04 ml NaOH per 1 g) between tests and laboratories, ensuring reliable data.

Applications

• Dairy Quality Control
  Ensures consistent acidity profiles in casein ingredients, critical for end-use applications including cheese production, nutritional products, and industrial formulations.

• Product Development and Research
  Enables formulation optimization by accurately assessing the acid balance in caseins derived from various processing routes (acid, fermentation, or rennet).

• Regulatory Compliance
  Provides a standardized method accepted internationally for laboratory accreditation, product specification, and export/import quality assurance.

• Industry Benchmarking
  Facilitates comparison of free acidity values across suppliers and product batches, promoting standardization in international dairy trade.

Related Standards

• ISO 5550 | IDF 78 – Determination of moisture content of caseins and caseinates
• ISO 707 | IDF 50 – Guidance on sampling of milk and milk products for laboratory testing
• ISO 385 – Laboratory glassware - Burettes
• ISO 648 – Laboratory glassware - Single volume pipettes
• ISO 835 – Laboratory glassware - Graduated pipettes
• ISO 3310-1 – Test sieves - Requirements for metal wire cloth sieves
• ISO 4788 – Laboratory glassware - Graduated measuring cylinders

These related standards provide the laboratory controls and sampling frameworks supporting reliable free acidity measurement per ISO 5547:2008.

By following ISO 5547:2008, dairy laboratories can achieve consistent, accurate, and internationally comparable determinations of free acidity in caseins, supporting quality assurance and product integrity in dairy manufacturing and trade.