A rapid detection method based on helicase-dependent isothermal DNA amplification (HDA) was established for Lactobacillus plantarum in fermented milk. Specific primers were designed according to the scrB gene sequence of Lactobacillus plantarum (Genbank Accession NO. AJ579541.1), and the optimal concentrations of UvrD helicase and T4 gp32 in the reaction system were determined through experiments. The limit of detection (LOD), specificity, consistency and stability of the proposed method were evaluated by use of L. plantarum-spiked samples, amplification of various strains, and electrophoresis of amplified products and sequence alignment analysis, respectively. The results showed that the optimized of UvrD helicase and T4 gp32 in the reaction system were found to be 0.15 and 5.0 μg, respectively. The HDA method had high specificity with no amplification of other strains tested. The detection limit was 2.8 × 10¹ CFU/g. The amplified product was consistent with the designed sequence length (273 bp) and the sequence homology was 100%. In conclusion: this method is rapid, simple, sensitive and suitable for the detection of Lactobacillus plantarum in fermented milk.

A quality control sample for the qualitative analysis of Listeria monocytogenes was developed by vacuum freezing drying technology, and the homogeneity and stability of the quality control sample were systematically analyzed. By optimizing the type of lyophilized matrix, the optimal conditions for the development of quality control samples were obtained. The homogeneity and stability of the developed quality control sample were verified by counting the number of cells as well as using matrix-assisted laser desorption ionization time-of-flight mass spectrometry. The quality control sample was white in color, spherical in shape and uniform in size. The results of cell counting for uniformity validation showed F = 0.567, which was less than the critical value, indicating good uniformity. In the transportation stability test, the quality control sample remained stable at 37 and 25 ℃. In the storage stability test, the resurrection rate of the quality control sample was 101.5% after 28 days of storage at –20 ℃, and 99.6% after 28 days of storage at 4 ℃, indicating that the sample has good uniformity and stability, and can be used as a positive quality control sample for the detection and quality control of Listeria monocytogenes.

In this study, an instant quality control sample for the detection of Salmonella enteritidis in meat products by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) was developed. The homogeneity and stability of the quality control sample were verified by culture counting, MALDI-TOF-MS analysis and statistical analysis. The quality control sample was found to be white in color and spherical in shape. In the homogeneity test, the results of culture counting showed F = 0.75, which is less than the critical value, indicating that the homogeneity is consistent. The transport stability test showed that the number of viable bacteria in the quality control sample was stable and grew well at 37 and 25 ℃. The storage stability test showed that the resuscitation rate of the quality control sample was 90.6% after 28 days of storage at −20 ℃ and 89.0% after 28 days of storage at 4 ℃, indicating that the sample was stable in nature and could be stored stably for a long period of time. Similarly, the results of each MALDI-TOF-MS cycle were stable. In conclusion, the instant quality control sample for the rapid detection of S. enteritidis developed in this study has good homogeneity and stability, and can be used as a positive quality control sample for the detection and quality control of S. enteritidis.

This paper developed a ready-to-use quality control sample which can be directly used without secondary culture for the rapid detection of Escherichia coli in meat and meat products by matrix assisted laser desorption/ionization time-offlight mass spectrometry (MALDI-TOF-MS). The sample was evaluated for homogeneity and stability. The results showed that the survival rate of the quality control sample prepared using the selected cryoprotectant was above 90%. The culture count result of the quality control sample (F = 0.567) was less than the critical value, suggesting good uniformity. The quality control sample was stable for 14 days at 37 and 25 ℃, and the resuscitation rates were 101.5% and 99.6% at −20 and 4 ℃ for 28 days, respectively. After 28 days of storage at 37 and −20 ℃, the results of MALDI-TOF-MS were consistent, indicating that the developed sample had good stability and met the requirements of quality control samples.

A droplet digital polymerase chain reaction (ddPCR) method for the quantitative detection Acetobacter aceti in fermented milk was established. Specific primers and probes were designed according to the internally transcribed spacer (ITS) gene sequence of Acetobacter aceti, and annealing temperature was optimized. The specificity of the method was verified by applying it on various strains, the limit of detection (LOD) was determined for artificially inoculated Acetobacter aceti, and the absolute quantification was systematically investigated by comparing the results of ddPCR and the counting results. The experimental results showed that the optimal annealing temperature was 54.6 ℃, the method had strong specificity and high sensitivity, and the LOD was 7.2 × 10¹ CFU/mL. The quantitative deviation rate was 23.73%. This method can meet the demand for quantitative detection of Acetobacter aceti in fermented milk.