ISO 8968-1:2014

Overview

ISO 8968-1:2014 (IDF 20-1:2014) specifies a laboratory method for determining nitrogen content and calculating crude protein in milk and milk products using the Kjeldahl principle. The standard covers both traditional and block digestion procedures and sets out reagents, apparatus, sampling, test procedures, calculation, precision and reporting requirements for reliable milk analysis and dairy testing.

Key topics and technical requirements

• Scope and applicability: Applies to liquid cow’s, goat’s and sheep’s whole, partially skimmed or skimmed milk; hard, semi‑hard and processed cheese; and dried milk and dried milk products (including infant formulae, milk protein concentrate, whey protein concentrate, casein and caseinate). Not applicable to samples containing ammonium caseinate.
• Principle: Organic nitrogen is converted to ammonium sulfate by digestion with concentrated sulfuric acid (with potassium sulfate and copper(II) sulfate catalyst). After addition of excess NaOH, liberated ammonia is steam‑distilled into boric acid and titrated (typically with 0.10 mol/L HCl) to determine nitrogen, from which crude protein is calculated.
• Reagents and apparatus: Standard lists include potassium sulfate, copper(II) sulfate catalyst, sulfuric acid (95–98 %), sodium hydroxide solution, boric acid solution, and standardized HCl titrant, plus balances, digestion equipment (traditional or block), distillation apparatus and burettes or automated titrators.
• Sample preparation and procedures: Detailed instructions for preparing test portions of liquid milk, cheese and dried products, blank and recovery tests, and both traditional and block digestion workflows.
• Calculation, expression and precision: Procedures for converting titration data into nitrogen content and crude protein, method precision (repeatability/reproducibility) and required elements of the test report.

Practical applications and users

• Quality control laboratories in dairy processing plants for nutritional labeling and routine product checks.
• Regulatory and compliance testing to verify protein content claims and meet food standards.
• Research and development groups validating formulations, infant formula, protein concentrates and cheese composition.
• Third‑party testing laboratories offering contract dairy analysis services.

ISO 8968-1 is essential where accurate Kjeldahl protein determination, standardized test methods and traceable results are required for milk and milk‑derived products.

Related standards

• ISO/IDF standards in the 8968 and 20 series (related parts and historical revisions)
• Normative references cited within ISO 8968-1, e.g. ISO 385 (burettes) and ISO 8655‑3 (piston burettes)

Keywords: ISO 8968-1, Kjeldahl principle, nitrogen content, crude protein, milk analysis, dairy testing, IDF 20-1, Kjeldahl method, protein determination.