Overview
ISO 27871:2011 (IDF 224:2011) specifies a laboratory method for determining the nitrogenous fractions in cheeses and processed cheese made from cow’s milk. The standard defines how to separate and quantify soluble nitrogen (SN) and two specific soluble fractions - TCA‑SN (trichloroacetic acid soluble nitrogen) and PTA‑SN (phosphotungstic acid soluble nitrogen) - using precipitation, filtration and nitrogen determination by the Kjeldahl or block‑digestion methods (referencing ISO 8968‑1 and ISO 8968‑2).
Key topics and requirements
- Scope: Applies to cheeses and processed cheeses from cow milk.
- Principle: Prepare a citrate solution of crushed cheese, precipitate insoluble components:
- at pH 4.4 for SN,
- in 12% TCA for TCA‑SN,
- in 5% PTA (with sulfuric acid) for PTA‑SN.
Filtrates are analysed for nitrogen content using the Kjeldahl or block‑digestion method.
- Reagents & apparatus: Specifies analytical reagents (trisodium citrate, 24% TCA, 25% PTA, HCl, sulfuric acid) and common lab equipment (homogenizer, pH meter, filtration 8 µm, volumetric glassware).
- Sample preparation: Remove rind/mould, grind or grate to a representative test sample, avoid moisture loss, and analyse promptly or preserve appropriately.
- Analytical steps: dissolution in citrate solution, pH adjustment, precipitation, filtration, digestion and Kjeldahl determination of nitrogen.
- Calculations & reporting: Formula for converting measured acid volumes and titrations into grams N per 100 g sample; results expressed to two decimal places. A blank test is mandatory.
- Precision: Repeatability and reproducibility limits are given (examples: repeatability for SN at pH 4.4 = 0.053 g N/100 g; reproducibility for SN at pH 4.4 = 0.089 g N/100 g).
- Test report: Must include sample ID, sampling method, reference to ISO 27871:2011, operating details, results and any checked repeatability.
Applications and users
ISO 27871:2011 is used for:
- Quality control in dairy and processed cheese production to monitor protein breakdown and maturation.
- Product specification and labeling where nitrogen/peptide content is relevant.
- Research and development studying proteolysis, ripening, and texture/flavor relationships.
- Regulatory and conformity testing by food laboratories and inspection authorities.
Primary users: dairy laboratory analysts, QC/QA managers, R&D scientists, regulatory laboratories and accreditation bodies.
Related standards
- ISO 8968‑1 / IDF 20‑1 and ISO 8968‑2 / IDF 20‑2 - Kjeldahl and block‑digestion nitrogen determination (normative references).
- ISO 707 - sampling of milk and milk products (recommended).
- ISO 5725 - precision of measurement methods (interlaboratory study guidance).
- Supporting ISO references for glassware and water quality (ISO 3696, ISO 1042, ISO 4788, ISO 835).
Keywords: ISO 27871:2011, cheese nitrogen fractions, soluble nitrogen (SN), TCA‑SN, PTA‑SN, Kjeldahl, citrate solution, cheese quality control.