DIN EN ISO 8968-4:2016-09

This part of ISO 8968|IDF 20 specifies a method for the direct and indirect determination of the protein nitrogen content of liquid, whole or skimmed milk. Indirect determination of protein nitrogen: precipitation of protein from a test portion by adding an appropriate amount of trichloroacetic acid to give a final concentration of trichloroacetic acid in the mixture of approximately 12 %. Filtering off the precipitated milk protein, the non-protein nitrogen compounds remain in the filtrate. Determine the nitrogen content according to the method described in ISO 8968-1|IDF 20-1. Direct determination of protein nitrogen: precipitate the protein from a weighed sample by adding an appropriate amount of trichloroacetic acid to give a final concentration of trichloroacetic acid in the mixture of approximately 12 %. Separate the protein precipitate by filtration. (The precipitate contains the protein nitrogen content of the sample.) Determine the nitrogen content of the precipitate by the method described in ISO 8968-1 IDF|20-1. This standard is intended to replace DIN EN ISO 8968-4:2002-06 and DIN EN ISO 8968-5:2002-06. Compared to these standards, the title of the standard has been supplemented, the scope of application has been specified and precision data have been revised. Furthermore, an informative annex with interlaboratory test results has been included and the text editorially and technically revised and adapted to the currently valid design rules. This document has been prepared by Subcommittee SC 5 "Milk and milk products" (secretariat: NEN, The Netherlands) of Technical Committee ISO/TC 34 "Food products" (secretariat: AFNOR, France) in collaboration with Technical Committee CEN/TC 302 "Milk and milk products - Methods of sampling and analysis", the secretariat of which is held by NEN (The Netherlands). The responsible committee is NA 057-05-13 AA "Milch und Milchprodukte - Probenahme- und Untersuchungsverfahren" ("Milk and milk products - Methods of sampling and analysis") at DIN.