Overview
ISO 9622:2013 (IDF 141:2013) provides international guidelines for applying mid‑infrared (MIR) spectrometry to the quantitative compositional analysis of milk and liquid milk products. It covers measurement of absorption in the mid‑infrared region to estimate constituents and physico‑chemical parameters for matrices such as raw milk, processed milk, cream and whey. The standard is primarily written for cow’s milk but is also applicable to milk from other species (goat, ewe, buffalo) and derived liquid products when appropriate calibrations and controls are in place. Applications are limited to lower‑viscosity products that can be pumped through the analyser flow system and to analytes that do not cause optical saturation at the wavelengths used.
Key Topics and Requirements
- Principle: MIR spectral absorbance is converted to constituent concentrations using calibration models developed from representative reference samples.
- Instrument characteristics: Describes instrument types (Fourier‑transform or filter‑based), wavelength selection and the role of additional built‑in sensors (e.g., conductivity sensors).
- Calibration approaches:
- Spectral calibration models using multiple wavelengths and/or additional sensor signals.
- Slope and intercept calibration (simple linear regression) for routine adjustment against reference methods.
- Factors affecting measurements:
- Instrument factors: repeatability testing (minimum replicate runs), zero stability monitoring, linearity checks and homogenizer performance.
- Physico‑chemical/biological factors: sample pretreatment, matrix differences, and potential optical saturation.
- Sampling and determination: Guidance on representative sampling, pretreatment (homogenization) and measurement procedures.
- Quality control and monitoring:
- Daily stability checks using control samples.
- Procedures for checking slope/intercept and re‑adjusting instrument settings.
- Precision: Definitions and expectations for repeatability, intra‑laboratory reproducibility and inter‑laboratory reproducibility.
- Reporting: Required elements in the test report and referencing normative methods.
Practical Applications & Users
- Who uses ISO 9622:2013:
- Dairy quality control laboratories and plant QC teams
- Instrument manufacturers and calibration service providers
- Regulatory laboratories and accreditation bodies
- Research groups developing spectral calibrations for novel matrices
- Typical uses:
- Rapid routine analysis of fat, protein, lactose and other milk constituents
- Monitoring compositional changes during processing
- Supporting payment systems and quality assurance programs
- Integrating additional sensor data (e.g., conductivity, freezing point equivalents) into spectral models
Related Standards (if applicable)
- ISO 8196 | IDF 128 - overall accuracy of indirect milk analysis methods
- ISO 8968-1, -2, -5 | IDF 20 parts - nitrogen/protein reference methods (Kjeldahl, block digestion, protein‑nitrogen)
Keywords: ISO 9622:2013, mid-infrared spectrometry, MIR, milk analysis, milk composition, infrared spectroscopy, calibration, homogenization, repeatability, milk quality control.
Open preview (PDF)Milk and liquid milk products — Guidelines for the application of mid-infrared spectrometry
