DIN 10470:2011-07

This standard specifies a derivative spectroscopic method for determination of whey protein content and casein content in total protein. It is applicable for milk, milk powder and cream cheese. To allow for exposure of the protein-bound aromatic amino acids and to achieve a homogeneous environment for the chromophore groups, the samples are diluted with 6 mol/l guanidinium chloride. The determination of the whey protein or casein content in total protein is carried out by UV derivative spectroscopic method. The quantitative analysis is carried out with the second derivation by means of UV absorption of the amino acids tryptophan and tyrosine, the characteristic maxima and minima are between 270 nm and 300 nm in the derivative spectrum. The (Q_D-value) calculated form the maxima or minima at 283 nm, 287 nm, 290 nm and 294 of the derivative spectrums results in a linear correlation to the whey protein and casein content in the total protein from milk and milk products. Calibration of the method is carried out using reference samples which have a known casein/milk protein ratio. With respect to DIN 10470:1999-07, only the measurement and analysis of the derivative spectrums with second derivation have been described and the results of a round robin test for validation of the method has been incorporated. Annex A (Preparation of reference samples) and Annex C (device-independent evaluation algorithm for calculation of derivative spectrums) have been deleted, analysis is described in clause 8 and the spectrum illustrated in Figure 1 has been updated. Furthermore, the duration of usability of the sample and calibration solutions given and it is specified that the values measured by the spectrophotometer and used for calculation shall show at least three significant spaces after the decimal points and correlation coefficient of the calibration line obtained shall be at least 0,99. The standard has been technically and editorially revised and supplemented and has been adapted therewith to the currently valid design rules. This document has been prepared by the Food and Agricultural Products Standards Committee, Working Committee NA 057-05-13 AA "Milch und Milchprodukte - Probenahme- und Untersuchungsverfahren" ("Milk and milk products - Methods of sampling and analysis").