Matrix uncertainty in feeding-stuffs according to ISO 19036:2019

The combined measurement uncertainty of quantitative microbiological methods in the area of food and feed is calculated according to ISO 19036:2019 from the technical (intra-laboratory reproducibility standard deviation), the distributional and the matrix uncertainty (umatrix) of the respective sample type. The matrix uncertainty is a property of a certain sample type and independent of the individual laboratory and analysis, respectively. This study broadens the, so far, comparatively small data base on matrix uncertainties for feeding stuffs by investigating 20 representative feed types in 46 sample series. Thereby, difficulties and limitations arising from sample preparation, the selection of different microbial groups (bacteria and fungi) and the nature of different feed types are highlighted. In addition, the applicability with industrially added feed additives (e.g. probiotics) is discussed. In conclusion, the postulated independence and scope of the matrix uncertainty are limited in these respects.