Overview
ISO 17129:2006 (IDF 206:2006) specifies a screening method for detecting and quantifying soy and pea protein isolates in low‑heat milk powder using capillary electrophoresis in the presence of sodium dodecyl sulfate (SDS‑CE). The standard describes sample preparation, reagent formulations, CE operating conditions and calculation rules to express soy/pea proteins as a mass fraction of total protein. Note: the method is not suitable for detecting hydrolysed plant proteins.
Key topics and technical requirements
- Scope: Screening and quantification of soy and pea proteins in low‑heat milk powder; expressed relative to total protein (total protein calculated from nitrogen, e.g., ISO 14891 or ISO 8968 methods).
- Sample preparation: Selective removal of milk proteins with a tetraborate‑EDTA extraction buffer; washed residue is dissolved in a sample buffer containing Tris‑HCl, SDS and a reducing agent (2‑mercaptoethanol), heated at 95 °C for 10 min and centrifuged.
- Buffers & pH control: Extraction buffer pH ~8.3; sample buffer pH ~8.7. Use analytical‑grade reagents and high‑purity water.
- Capillary electrophoresis (SDS‑CE):
- Hydrophilically coated fused‑silica capillary (~20 cm effective length, 75 µm i.d.).
- UV detection at approximately 214 nm.
- Linear voltage gradient (example: start 2 kV to 7 kV over run).
- Dedicated capillary and instrument flushing routines (NaOH and electrophoresis buffer).
- Calibration & references: Quantification requires calibration with a reference sample calibrant (e.g., supplied by NIZO) and a reference protein test mix (10–200 kDa).
- Performance & reporting: Precision assessed by interlaboratory trials; repeatability and reproducibility are addressed. Sampling is outside the method (ISO 707 recommended).
Applications and users
- Food control laboratories testing milk powder authenticity and compliance with compositional standards (to detect adulteration with plant proteins).
- Dairy manufacturers and quality control (QC) teams verifying raw material and finished product integrity.
- Regulatory agencies enforcing labeling and compositional rules.
- Contract testing labs offering targeted screening for soy and pea adulteration in dairy powders.
Related standards
- ISO 14891 | IDF 185 - Determination of nitrogen (Dumas) for total protein.
- ISO 8968 | IDF 20 - Determination of nitrogen/protein in milk (various parts).
- ISO 707 | IDF 50 - Recommended sampling of milk powder.
Keywords: ISO 17129:2006, milk powder, soy protein, pea protein, SDS‑CE, capillary electrophoresis, screening method, sodium dodecyl sulfate, dairy testing, food authenticity.