Overview
ISO 9233-2:2018 (IDF 140-2:2018) specifies a high-performance liquid chromatography (HPLC) method for the determination of natamycin in cheese, cheese rind and processed cheese. The standard covers quantitative determination of natamycin mass fraction (expressed in mg/kg) for concentrations above 0.5 mg/kg and the surface‑area‑related natamycin mass in cheese rinds above 0.03 mg/dm². It is a validated analytical procedure intended for laboratory testing, quality control and regulatory monitoring.
Key topics and technical requirements
- Analytical principle: Extraction with methanol, dilution with water, cooling (−15 °C to −20 °C) to precipitate fat, filtration, optional concentration and HPLC analysis.
- HPLC conditions and detection: UV detection at 303 nm; recommended analytical column C8 (150 mm × 4.6 mm, 5 µm) with a guard column (≈100 mm × 2.1 mm, 30–40 µm).
- Standards and reagents: Preparation of natamycin standard stock (500 mg/L) and working solution (≈5 µg/mL) in methanol/aqueous methanol; use of analytical‑grade solvents (methanol, acetic acid).
- Sample preparation: Specific instructions for cheese rind sampling (slice off up to 5 mm rind, measure surface area in dm²), grinding/mixing, and test portion preparation for rind and interior/processed cheese.
- Fat removal and cleanup: Cold precipitation of fat followed by filtration; optional use of solid‑phase extraction (e.g., C18 cartridges) to concentrate low-level samples.
- Calibration and quantification: Construction of calibration graphs, adjustments for low natamycin content, calculation formulas for mass fraction and surface-area-related mass.
- Quality data: Includes sections on precision (repeatability and reproducibility) and results from interlaboratory trials (Annex B), plus examples (Annex A) and required elements for the test report.
Applications and users
ISO 9233-2:2018 is used for:
- Regulatory compliance testing by food control authorities and labs to verify natamycin use on cheeses.
- Quality control in dairy processing plants and contract testing laboratories to monitor preservative levels.
- Research and development for formulation trials or stability studies involving natamycin-coated rinds or processed cheese.
- Import/export inspection, providing reproducible, internationally accepted analytical results.
Intended users include analytical chemists, dairy laboratories, food safety regulators, and manufacturers of cheese and processed cheese.
Related standards
- ISO 9233 series (other parts address alternative methods or sampling).
- ISO 707 | IDF 50 (recommended sampling for milk and milk products) - referenced as a sampling guideline though sampling itself is not part of ISO 9233-2.
Keywords: ISO 9233-2:2018, natamycin, HPLC method, cheese rind, processed cheese, natamycin determination, analytical method, food testing.