Overview
EN ISO 20483:2013 - equivalently ISO 20483:2013 - defines the Kjeldahl method for determination of nitrogen content and calculation of crude protein in cereals, pulses and derived products. Published by CEN/ISO, the standard specifies sample preparation, reagents, apparatus, test procedure (digestion, distillation and titration), expression of results and precision criteria. It notes that the method does not distinguish protein nitrogen from non‑protein nitrogen and that full recovery of nitrates/nitrites may not always be possible.
Key topics and technical requirements
- Scope and principle
- Applicable to cereals, pulses and derived products.
- Principle: acid digestion (sulfuric acid + catalyst), alkalization, steam distillation, ammonia capture in boric acid and titration to quantify nitrogen, then conversion to crude protein.
- Reagents and materials
- Specified reagents include concentrated sulfuric acid (c ≈ 18 mol·L−1), Kjeldahl catalyst tablets (CuSO4/TiO2/K2SO4 mix), boric acid trapping solution, indicators (bromocresol green/methyl red), and standardized titrants (e.g. H2SO4 0.05 mol·L−1).
- Apparatus and procedure
- Requirements for digestion and distillation apparatus, anti‑foaming measures, blank determinations and reference/material check tests.
- Sampling and sample preparation
- Directions for sampling representative test portions and determining moisture content prior to protein calculation (see normative moisture methods).
- Results and quality criteria
- Expression of nitrogen and crude protein as mass fraction (percentage of dry product).
- Annexes provide interlaboratory test results, repeatability/reproducibility limits and critical difference guidance.
- Conversion
- Annex C lists factors for converting nitrogen to protein appropriate to different cereals/pulses.
- Safety
- Standard includes a safety warning: users must apply appropriate laboratory safety and regulatory practices when handling hazardous reagents and operations.
Applications and users
- Routine and official laboratory analysis for:
- Grain, flour and pulse quality control (milling, processing).
- Trade and specification verification for cereal and legume shipments.
- Food industry R&D and formulation (protein labelling and nutritional analysis).
- Regulatory and inspection labs requiring standardized protein determination.
- Typical users: analytical chemists, food technologists, grain traders, quality assurance teams and accreditation bodies.
Related standards
- ISO 712 - moisture content (reference method)
- ISO 6540 - maize moisture (milled/whole grains)
- ISO 24557 - pulses moisture (air‑oven method)
EN ISO 20483:2013 is the authoritative reference when using the Kjeldahl method for cereals and pulses and should be used alongside the listed moisture standards and applicable laboratory QA procedures.
