ISO 8968-4-2016 PDF

Full title and description

Milk and milk products — Determination of nitrogen content — Part 4: Determination of protein and non-protein nitrogen content and true protein content calculation (Reference method). This International Standard specifies reference procedures for determining protein-nitrogen and non‑protein‑nitrogen (NPN) in liquid milk (whole or skimmed) and provides the method to calculate true protein content from measured nitrogen fractions.

Abstract

ISO 8968-4:2016 (IDF 20-4:2016) defines both direct and indirect reference methods for measuring protein nitrogen and non‑protein nitrogen in milk and describes the calculation used to express true protein content. It is intended as a laboratory reference method to support accurate reporting, method validation, and comparison of routine methods.

General information

• Status: Published (confirmed current on review in 2021).
• Publication date: 4 April 2016 (Edition 2, 2016).
• Publisher: International Organization for Standardization (ISO) / published jointly as IDF 20-4.
• ICS / categories: 67.100.10 (Milk and processed milk products).
• Edition / version: Edition 2 (2016).
• Number of pages: 11 (ISO edition; national adoptions may show different formatting/page counts).

Sources: ISO bibliographic record and national adoption notices.

Scope

ISO 8968-4:2016 specifies reference procedures for the direct and indirect determination of protein nitrogen and non‑protein nitrogen in liquid milk (whole or skimmed) and the calculation of true protein content. The standard is focused on laboratory reference methodology rather than rapid routine screening techniques. It complements the Kjeldahl principle and crude protein calculation described in ISO 8968‑1.

Key topics and requirements

• Reference procedures for determination of protein-nitrogen and non‑protein‑nitrogen (NPN) in liquid milk.
• Calculation method to convert measured nitrogen fractions into true protein content (including use of appropriate nitrogen‑to‑protein conversion).
• Details on sample preparation and analytical steps for direct and indirect determinations (digestion/distillation/titration and measurements required for NPN).
• Use as a reference (validation and comparison) method; relationship to Kjeldahl-based crude protein methods covered in ISO 8968‑1.
• Specification of reporting units, calculation expressions, and precision expectations suitable for laboratory use and regulatory comparison.

Typical use and users

Primary users are national and commercial testing laboratories, dairy industry quality-control teams, regulatory bodies, standards bodies, and research organizations that need a validated reference method for protein and NPN determinations in milk. The standard is used for method validation, proficiency testing, calibration of routine methods, and dispute resolution where accurate true protein values are required.

Related standards

ISO 8968-4:2016 is part of the ISO 8968 series (Determination of nitrogen content). Related documents include ISO 8968-1 (Kjeldahl principle and crude protein calculation), other parts of ISO 8968 (methods for powdered milk and other matrices), and the corresponding IDF publication (IDF 20-4:2016). National and regional adoptions (EN/ISO variants) reflect the same content with local implementation notes.

Keywords

milk, milk products, nitrogen determination, protein nitrogen, non‑protein nitrogen (NPN), true protein, reference method, Kjeldahl, ISO 8968, IDF 20-4.

FAQ

Q: What is this standard?

A: ISO 8968-4:2016 is an international reference standard that specifies methods for determining protein nitrogen and non‑protein nitrogen in liquid milk and for calculating true protein content. It is published by ISO and issued jointly with IDF (IDF 20-4:2016).

Q: What does it cover?

A: It covers laboratory reference procedures (direct and indirect) for measuring protein‑nitrogen and NPN in whole and skimmed liquid milk, the calculations to express true protein, sample preparation essentials, and reporting conventions. It is intended for use as a reference for validating routine methods.

Q: Who typically uses it?

A: Accredited testing laboratories, dairy industry QC/QA staff, regulators, research laboratories, and standards organizations use ISO 8968-4 for method validation, inter-laboratory comparison and where legally or contractually required reference values are needed.

Q: Is it current or superseded?

A: ISO 8968-4:2016 (Edition 2) is published and was reviewed/confirmed in 2021; at confirmation it remained the current edition. Users should always check national adoption records for specific implementation dates.

Q: Is it part of a series?

A: Yes — it is part 4 of the ISO 8968 series (Determination of nitrogen content in milk and milk products). Other parts of the series include the Kjeldahl principle and crude protein calculation (ISO 8968‑1) and additional parts covering different sample types or procedures.

Q: What are the key keywords?

A: milk, protein nitrogen, non‑protein nitrogen, NPN, true protein, reference method, Kjeldahl, ISO 8968, IDF 20-4.