ISO 21543:2020

Overview - ISO 21543:2020 (Milk and milk products - Guidelines for the application of near infrared spectrometry)

ISO 21543:2020 provides practical, method-oriented guidance for applying near infrared (NIR) spectrometry to the analysis of milk and milk products in liquid, semi‑solid or solid forms. The standard covers appropriate instrument setups (transmittance, diffuse reflectance, transflectance), sample presentation and handling, calibration and validation practices, performance statistics, and routine checks to ensure reliable quantitative results for typical dairy parameters.

Key technical topics and requirements

• Scope of NIR use: Guidance for NIR analysis of milk, cream, yoghurt, cheese, butter, dried milk, whey and protein powders - in liquid, semi‑solid and solid forms.
• Measurement principles: Definitions and practical considerations for transmittance, diffuse reflectance and transflectance measurement setups, including the importance of optical path length and appropriate optical configuration for each sample type.
• Calibration & validation:
  • Selection of representative calibration samples and link to reference analyses.
  • Development and validation of calibration models.
  • Procedures for detecting and handling outliers (x‑outliers, y‑outliers, combined).
  • Handling changes in instrument or measurement conditions and model re‑validation.
• Performance statistics: Recommended statistics for assessing model performance and prediction quality, including standard error of prediction (SEP), root mean square error of prediction (RMSEP), root mean square error of cross‑validation (RMSECV) and bias.
• Sampling and sample preparation: Practical guidance for preparing and presenting homogeneous test samples across matrices (liquids, semi‑solids, powders).
• Routine quality assurance: Use of control samples, instrument diagnostics, stability checks and running performance checks of calibrations to maintain accuracy and precision.
• Reporting: Elements to include in a test report to document NIR results and method conditions.

Practical applications and users

ISO 21543:2020 is intended for:

• Dairy industry quality control and production labs for rapid compositional analysis (fat, protein, moisture/total solids, lactose, salts, proximate parameters).
• Analytical laboratories implementing NIR methods as alternatives or complements to wet chemistry reference methods.
• Instrument manufacturers and method developers creating transflectance/reflectance/transmittance accessories and calibration software.
• Researchers and standard bodies developing or harmonizing NIR-based dairy testing protocols.

Benefits include faster throughput, non‑destructive testing, and robust routine monitoring when calibrations and QA procedures described in the standard are followed.

Related standards

ISO 21543:2020 is published jointly by ISO and IDF and complements other ISO/IDF standards for milk sampling and reference analytical methods. Users should consult applicable ISO/IDF dairy method standards and national regulations to align NIR results with official reference methods.