In order to provide a scientific rationale for the quality control in the determination of aerobic plate count (APC) in milk, the measurement uncertainty was estimated. According to the national standard of China (GB 4789.2—2016), APC in samples was detected. The sources of uncertainty were analyzed according to Evaluation and Expression of Uncertainty in Measurement (JJF 1059.1—2012) and a mathematical model for uncertainty evaluation was established. The introduced uncertainty components were evaluated and finally the total combined uncertainty was established by combination of individual components. The results showed that the extended uncertainty for APC quantification in milk samples was 0.043 4. The logarithm of APC was [3.924, 4.010], and from this, APC was calculated to be 8 395–10 233 CFU/mL. In conclusion, this procedure can effectively assess the measurement uncertainty in the determination of APC in milk.

In recent years, the addition of probiotics to milk powder has gradually become a research focus. In order to ensure the product quality and safety, a microbiological detection method for Lactobacillus fermentum CECT5716 in milk powder has been established. It was found that the population of Lactobacillus fermentum in milk powder could be accurately counted by spreading serial 10-fold dilutions in buffered peptone water (BPW) onto MRS plates and culturing them under anaerobic conditions at (36 ± 1) ℃ for (48 ± 2) h, with clear discrimination from inoculated bifidobacteria. This method was more suitable for counting Lactobacillus fermentum than the Chinese national standard method (GB 4789.35?2016), and had the advantages of high discrimination capacity, short culture time, simple operation, good repeatability, and high accuracy. This method also included 16S rDNA sequence analysis of the strain for its subsequent molecular identification. There was no significant difference in the accuracy of this method versus the national standard method in detecting 20 samples prepared in our laboratory (P = 0.127).