Overview
ISO 5739:2003 / IDF 107:2003 defines a standardized laboratory method for determining the content of scorched particles and extraneous matter in caseins and caseinates. The method specifies sample preparation, dissolution reagents, filtration, visual comparison with standard discs and result expression. It is intended for quality control, compliance testing and product characterization in the dairy and ingredient sectors.
Key topics and requirements
- Scope: Applies to caseins and caseinates; measures coloured (scorched) residues and foreign matter associated with production, storage or distribution defects.
- Principle: Dissolve a 25 g test portion in appropriate reagent (sodium carbonate, sodium polyphosphate, EDTA or sodium hydroxide), filter through a calibrated filtering disc, dry the disc and visually compare scorched particles against standard scorched-particle discs (A–D).
- Reagents: Examples specified include sodium carbonate, sodium polyphosphate, disodium EDTA, sodium hydroxide (~1 mol/L) and 95% ethanol for caseinates.
- Apparatus: Typical laboratory equipment plus specified items - analytical balance (0.1 g), 32 mm filtering discs (cotton preferred, retention 5–10 µm), filtering device (28.6 mm area), 500 µm test sieve (ISO 3310-1), water bath at 60 °C and ×25 microscope.
- Sampling & test portion: Sampling guidance referenced (ISO 707 recommended). Test portion: 25.0 g; sample may be sieved (500 µm) and ground if necessary.
- Procedure controls: pH of solutions can affect partial solubility - pH should be checked and recorded. Heating step limited (dissolution ≤ 45 min at 60 °C).
- Evaluation & precision: Results are classified by comparison to standard discs; the standard includes precision data (repeatability and reproducibility) and prescribes reporting elements.
- Normative annexes: Annex A (testing filter discs) and Annex B (preparation of standard scorched-particle discs).
Applications and users
- Who uses it: Dairy ingredient manufacturers, quality control and analytical laboratories, regulatory and inspection bodies, and R&D teams working with milk-protein ingredients.
- Practical uses:
- Routine QC of casein/caseinate lots prior to shipment or processing.
- Investigations of production or storage defects (burning, contamination).
- Establishing supplier quality agreements and acceptance criteria.
- Supporting regulatory compliance and product specifications.
Related standards
- ISO 3310-1 (test sieves) - referenced for sieve requirements.
- ISO 707 - recommended sampling method for milk powders and similar products.
- Method origin note: Procedure derived from USDA dry-milk scorched-particle methods; joint ISO/IDF/AOAC work.
Keywords: ISO 5739:2003, caseins and caseinates, scorched particles, extraneous matter, filtering discs, sodium carbonate, EDTA, quality control, dairy analysis.