关键词: 不确定度评定；“自上而下”法；技术不确定度；基质不确定度；泊松分布不确定度；基于最可能数不确定度；确证不确定度

Abstract: On the basis of Microbiology of the food chain-Estimation of measurement uncertainty for quantitative determinations (ISO 19036) and Guidelines for the estimation of measurement uncertainty of food microbiological quantitative detection (RB/T 228-2023), the top-down method was used to design an experimental scheme for uncertainty evaluation in three different quantitative assays by using raw and fermented milk as samples. The uncertainty evaluation for total colony number included technical uncertainty (utech), matrix uncertainty (umatrix) and Poisson distribution uncertainty (upoisson); when the result was 9.4 × 104 CFU/mL, the extended uncertainty was 0.31 (lg (CFU/mL)). The uncertainty evaluation for maximum probable number (MPN) included utech, umatrix, and uncertainty based on the most probable number (uMPN); when the result was 24 MPN/g, the extended uncertainty was 0.94 (lg (MPN/g)). The uncertainty evaluation for total colony number that needs to confirm target microorganisms included utech, umatrix, upoisson, and confirmatory uncertainty (uconf); when the result was 22 CFU/g, the extended uncertainty was 0.29 (lg (CFU/g)).

Key words: evaluation of uncertainties; top-down method; technical uncertainty; matrix uncertainty; Poisson distribution uncertainty; uncertainty based on most probable number; confirmatory uncertainty