ISO 17997-2-2004 PDF

Full title and description

ISO 17997-2:2004 (IDF 29-2:2004) — Milk — Determination of casein‑nitrogen content — Part 2: Direct method. Specifies a routine laboratory procedure for the direct determination of the casein‑nitrogen content of bovine milk; the procedure can be adapted for milk from other species and for liquid dairy products.

Abstract

This standard defines a practical, routine method to determine the nitrogen content of casein precipitated directly from milk. The method uses controlled acidification to precipitate casein, separation of the casein fraction and subsequent determination of nitrogen (typically by Kjeldahl or equivalent digestion/titration techniques). Results are expressed as casein‑nitrogen and may be converted to casein (protein) using the appropriate conversion factor.

General information

• Status: Published (confirmed).
• Publication date: 21 September 2004.
• Publisher: International Organization for Standardization (ISO); also published jointly as IDF 29-2:2004.
• ICS / categories: 67.100.10 — Milk and processed milk products.
• Edition / version: Edition 1 (2004).
• Number of pages: 7.

Scope

ISO 17997-2:2004 specifies a routine direct method for determining the casein‑nitrogen content of bovine milk. The scope covers routine laboratory application for raw and processed liquid milks; the method may be modified where necessary for milk from other species or for other liquid dairy products. It is intended for quality control and compositional analysis rather than as the primary reference (see Part 1, the indirect/reference method).

Key topics and requirements

• Principle: selective precipitation of casein by controlled acidification (pH adjustment), separation of the precipitated casein fraction, and determination of nitrogen in that fraction.
• Reagents and buffer: defined acid and acetate/buffer solutions to reach the required precipitation pH (method specifies reagent concentrations and preparation).
• Apparatus: standard laboratory glassware, analytical balance, centrifuge or filtration equipment for separation, filter papers, digestion apparatus for Kjeldahl or block digestion, titration equipment.
• Sample preparation: warming and homogenization to dissolve fat, specified sample mass/volumes, and temperature control to ensure reproducible precipitation.
• Procedure steps: addition of acid/buffer to precipitate casein, settling or centrifugation/filtration of precipitate, rinsing, and digestion of the precipitate for nitrogen determination; inclusion of blanks and controls.
• Calculation and reporting: calculation of casein‑nitrogen from measured nitrogen in the precipitate; guidance to convert to casein (protein) using established conversion factors and to report units and precision.
• Performance characteristics: instructions on precision, repeatability and acceptance criteria; references to interlaboratory precision practices.
• Limitations and interferences: notes on matrix effects, proteolysis, fat removal, and the need to adapt sample handling for different species or processed products.

Typical use and users

Used by dairy quality control and analytical laboratories, milk processors, regulatory and standards bodies, and research groups. Typical applications include routine compositional testing, product specification verification, cheese‑yield estimation and research into milk protein composition.

Related standards

Commonly cross‑referenced standards include ISO 17997-1:2004 (IDF 29-1) — Part 1: Indirect (reference) method; the ISO/IDF series on nitrogen/protein determination (for example ISO 8968 parts on Kjeldahl and protein calculations); and other dairy analytical standards covering protein fractions, fat and solids determination. National adoptions and translations (e.g., BS ISO versions, regional equivalents) and IDF publications may also be associated.

Keywords

casein, casein-nitrogen, milk, bovine milk, direct method, precipitation, Kjeldahl, IDF 29-2, ISO 17997-2, dairy analysis, protein determination, ICS 67.100.10

FAQ

Q: What is this standard?

A: ISO 17997-2:2004 is an international standard (also published as IDF 29-2:2004) that specifies a routine laboratory method for the direct determination of casein‑nitrogen in milk.

Q: What does it cover?

A: It covers the principle, reagents, apparatus, sample preparation, stepwise procedure, calculation and reporting for precipitating casein from milk and measuring the nitrogen content of that precipitate to determine casein‑nitrogen.

Q: Who typically uses it?

A: Dairy industry quality/control laboratories, milk processors, regulatory testing laboratories and researchers working on milk composition and product formulation.

Q: Is it current or superseded?

A: This edition was published on 21 September 2004 and, per ISO review records, was reviewed and confirmed current in 2023. It is therefore listed as a confirmed (current) International Standard.

Q: Is it part of a series?

A: Yes — it is Part 2 of ISO 17997. Part 1 (ISO 17997-1:2004 / IDF 29-1) describes the indirect (reference) method; the ISO/IDF family of standards also includes related methods for nitrogen and protein determination (ISO 8968 series) and other dairy analytical standards.

Q: What are the key keywords?

A: casein, casein‑nitrogen, milk analysis, direct method, precipitation, Kjeldahl, IDF 29-2, ISO 17997-2, dairy laboratory.