Overview
ISO 11866-2:2005 – Milk and milk products - Enumeration of presumptive Escherichia coli - Part 2: Colony-count technique at 44 °C using membranes – is an international standard developed jointly by ISO and the International Dairy Federation (IDF). This standard defines a method for enumerating presumptive Escherichia coli (E. coli) in dairy products, using a membrane-based colony-count procedure carried out at 44 °C. The standard is applicable to a broad range of milk and milk-derived products, including liquid and dried milks, whey, caseins and caseinates, cheeses, butter, frozen and dessert milk products, and cream.
This membrane filtration technique is the preferred method for samples suspected of containing high levels of E. coli (more than 100 per gram or 10 per millilitre), supporting rigorous microbiological quality control in dairy processing and food safety laboratories worldwide.
Key Topics
- Enumeration Principle: The method involves filtering prepared test samples through cellulose acetate membranes, incubating on selective agar media, and counting indole-positive colonies to determine presumptive E. coli content.
- Sample Types: Suitable for raw or processed milk, liquid milk products, dried dairy components, cheese variants, butter, frozen desserts, creams, and related products.
- Temperature Control: Incubation at 44 °C enhances selectivity for E. coli, reducing background flora interference.
- Resuscitation Step: Initial incubation on mineral-modified glutamate agar aids recovery of stressed or damaged E. coli cells.
- Detection & Enumeration: Indole-positive colonies are identified by color development, and results are calculated as colony-forming units (CFU) per gram or per millilitre.
- Repeatability: The method provides clear criteria for repeatability, supporting reliable microbial testing.
- Reporting Requirements: Results are reported with reference to ISO 11866-2, including detailed sample identification, method parameters, and observed results.
Applications
Implementing ISO 11866-2:2005 strengthens food safety management and regulatory compliance in the dairy industry:
- Quality Control in Dairy Processing: Detects and quantifies E. coli contamination, supporting food safety programs and shelf-life validation.
- Regulatory Compliance: Demonstrates adherence to national and international standards for microbiological quality of milk and milk products.
- Microbiology Laboratories: Provides a standardized protocol for consistent, reproducible enumeration of presumptive E. coli across various sample types.
- Product Development: Assists in evaluating the effectiveness of hygienic processes and new formulations by monitoring E. coli levels.
- Supply Chain Assurance: Extends to ingredients such as dried milk powders, whey, and caseinates, enabling oversight from raw material intake through to finished products.
Related Standards
For a comprehensive approach to microbiological analysis in dairy and food products, the following standards are relevant:
- ISO 7218: Microbiology of food and animal feeding stuffs – General requirements and guidance for microbiological examinations.
- ISO 8261 | IDF 122: Milk and milk products – Guidance on preparation of test samples, initial suspensions, and dilutions for microbiological examination.
- ISO 4833: Microbiology of food and animal feeding stuffs – Enumeration of microorganisms – Colony-count technique at 30 °C.
- ISO 7251: Microbiology of food and animal feeding stuffs – Detection and enumeration of presumptive E. coli – Most probable number technique.
- ISO 707 | IDF 50: Guidance on sampling of milk and milk products.
By following ISO 11866-2:2005, laboratories and dairy processors can confidently assess E. coli contamination, underpinning food safety for consumers and facilitating market access for dairy products globally.