Overview
ISO 21571:2005 - "Foodstuffs - Methods of analysis for the detection of genetically modified organisms and derived products - Nucleic acid extraction" - specifies general requirements and validated procedures for DNA extraction, purification and quantitation as part of nucleic-acid-based GMO testing. Designed for food matrices, the standard is also applicable to related matrices such as grains and animal feed. Methods and options are described in Annex A (DNA extraction/purification) and Annex B (DNA quantitation).
Key topics and requirements
- Objective: produce DNA of sufficient quality (integrity, purity, length) and quantity for downstream PCR-based GMO analysis.
- Methods: multiple extraction and purification principles are provided (e.g., organic extraction, precipitation, adsorption on solid matrices). Annex A lists specific protocols; Annex B covers physical, fluorescence, enzymatic and qPCR-based quantitation methods.
- Quantitation options: absorbance (spectrophotometry), fluorescent intercalating dyes, enzymatic (bioluminescence) and quantitative PCR - qPCR is recommended for degraded or low-DNA samples.
- Sample preparation: guidance on representative test portions, homogenization, grinding and pre-treatments (e.g., heating ≤ 40 °C, dissolving in water, freezing ≤ −20 °C, lipid removal with hexane). Typical test-portion sizes in Annex A are 200–500 mg for DNA-rich materials; practical upper recommendation is 2 g. At least two test portions must be extracted.
- Laboratory practice: contamination control, “forward flow” sample handling, physical segregation of pre- and post-amplification areas, and validation of methods per matrix (repeatability and reproducibility).
- Validation and matrix dependence: performance depends on commodity and processing; alternative protocols are acceptable only after validation on the specific matrix.
- Intellectual property: note that some silica-based methods may be subject to patent rights (e.g., EP 0389063/USP 5,234,809).
Applications and users
ISO 21571 is intended for:
- Food testing laboratories performing GMO detection by PCR
- Regulatory and conformity assessment bodies validating analytical chains
- Research and method-development teams establishing nucleic-acid workflows for food, grain, feed and composite matrices
- Providers of DNA extraction kits and laboratory SOPs who need to align with international best practice
Practical benefits include standardized sample prep, reduced PCR inhibition, consistent DNA quantitation, and improved inter-laboratory comparability for GMO testing.
Related standards
- ISO 21569 - Qualitative nucleic-acid based methods (GMO detection)
- ISO 21570 - Quantitative nucleic-acid based methods (GMO quantitation)
- ISO 21568 - Sampling for GMO analysis
- ISO 24276 - General requirements and definitions for nucleic-acid-based GMO methods
Keywords: ISO 21571:2005, nucleic acid extraction, DNA extraction, DNA quantitation, GMO detection, food testing laboratory, PCR inhibitors, food matrices, Annex A, Annex B.