CERTIFICATION REPORT: The certification of the concentration of somatic cells (somatic cell count, SCC) in cow's milk: ERM-BD001

Abstract

This report describes the production of ERM-BD001, which is a set of two milk powder materials certified for their concentration of somatic cells. These materials were produced following ISO 17034:2016 and were certified in accordance with ISO Guide 35:2006. Raw cow's milk was skimmed and cells enriched by means of microfiltration. Thereafter, the milk was converted into milk powders using spray-drying. Two cell count concentration levels were produced. A tailor-made processing procedure was developed to minimise the alteration of the cells during processing. The resulting milk powders were bottled, and packaged in sets (one set consisting of one bottle with low count and one bottle with high count material; ERM-BD001a and ERM-BD001b, respectively). Between unit-homogeneity was quantified and stability during dispatch and storage were assessed in accordance with ISO Guide 35:2006. The material was characterised by an inter-laboratory comparison of laboratories of demonstrated competence and adhering to ISO/IEC 17025:2017. Technically invalid results were removed but no outlier was eliminated on statistical grounds only. Uncertainties of the certified values were calculated in accordance with the Guide to the Expression of Uncertainty in Measurement (GUM) and include uncertainties related to possible inhomogeneity, instability and characterisation. The materials are intended for the calibration of methods for enumeration of somatic cells using fluoro-opto-electronic cell counters according to ISO 13366-2:2006 [5] and for the assessment of the method performance of somatic cell count (SCC) reference methods based on microscopy according to ISO 13366-1:2008 [6] and routine methods operating fluoro-opto-electronic cell counters according to ISO 13366-2:2006 [5]. As with any reference material, the materials can be used for establishing control charts or validation studies. The CRMs are available in 14 g milk powder portions in glass bottles that were filled and sealed under an atmosphere of argon. The minimum amount of sample to be used is 3 g.