Overview
ISO 9233-1:2018 (IDF 140-1:2018) specifies a validated molecular absorption spectrometric method for measuring natamycin in cheese rind. The method is intended for determining natamycin mass fraction above 0.5 mg/kg and surface-area-related natamycin mass above 0.03 mg/dm². The standard describes sample preparation, extraction, instrumental measurement and calculation procedures and notes that the method can be suitable for detecting migration of natamycin into the cheese interior.
Key topics and technical requirements
- Scope and limits: Targets natamycin concentrations > 0.5 mg/kg (mass fraction) and > 0.03 mg/dm² (surface-related mass).
- Principle: Extraction of a known rind sample with methanol, dilution with water, cooling (−15 °C to −20 °C) to precipitate fat, filtration and quantification by UV molecular absorption spectrometry.
- Reagents and standards: Use analytical-grade methanol, prepare natamycin standard stock (500 mg/L) and working solutions (≈5 µg/mL) as specified.
- Apparatus: UV spectrometer (300–340 nm range) with 10 mm cells, volumetric flasks, slicers/grinders, membrane filters (0.20 µm & 0.45 µm), freezer, extraction cartridges for concentration when needed.
- Sampling and sample prep: Whole cheese or representative segments; rind removal (max 5 mm thickness), area/mass determination, grinding and homogenization. Sampling guidance references ISO 707 | IDF 50.
- Procedures and calculations: Test portion selection, preparation of test and standard solutions, absorbance measurement, calculations of natamycin mass fraction and surface-area-related mass, result correction and reporting.
- Quality and performance: Includes provisions for detection/quantitation limits, low-content handling, and precision data from interlaboratory trials (repeatability and reproducibility).
Applications and users
ISO 9233-1:2018 is used by:
- Dairy quality-control laboratories monitoring preservative levels on cheese rind.
- Food safety authorities and regulatory labs verifying compliance with national and international limits for natamycin.
- Cheese manufacturers and R&D teams assessing coating treatments, preservative application uniformity and potential migration into cheese.
- Export/import compliance where standardized testing and traceable results are required.
Practical applications include routine surveillance, shelf-life studies, coating process validation, and forensic testing when natamycin migration needs confirmation.
Related standards
- Sampling guidance: ISO 707 | IDF 50 (recommended sampling method for milk and milk products).
- The document is part of the ISO 9233 / IDF 140 series; check the ISO website for other parts covering related matrices or methods.
Keywords: ISO 9233-1:2018, natamycin, cheese rind, molecular absorption spectrometric method, UV spectrometry, surface-area-related natamycin mass, analytical method, food safety, dairy testing.