In order to ensure the quality of raw milk and enrich quality control strains for the acceptance evaluation of culture media for the detection of coliform bacteria in raw milk, three brands of violet red bile agar (VRBA), violet red bile agar with 4-methylumbelliferyl-β-D-glucuronidehydrate (VRBA-MUG), lauryl tryptose broth (LST) and brilliant green lactose bile broth (BGLB) were selected and evaluated for their physical indicators such as appearance, pH and moisture content as well as microbial indicators such as growth rate and selectivity using the methods specified in China’s national standard for quality requirements for culture media and reagents in food microbiological examination (GB 4789.28-2013). Besides, using Citrobacter freundii ATCC 43864 as a reference strain, seven strains of C. freundii were selected for acceptance evaluation of the four media. The results showed that the color of all three brands of dry powdered media was normal. Their moisture content was 5%–6%, and their pH was in line with the national standard. The growth rate of the seven tested strains of C. freundii was greater than 0.7 on the three brands of VRBA and VRBA-MUG, while only CMCC 48098 and CICC 22910 achieved turbidity of 2 on the three brands of LST and BGLB, and produced gas in the catheter; the same results were obtained with ATCC 43864. In summary, the three brands of VRBA, VRBA-MUG, LST and BGLB all comply with GB 4789.28-2013, and CMCC 48098 and CICC 22910 can be recommended as supplements to quality control strains for the acceptance evaluation of the four media.

In order to evaluate the application value of ready-to-use Salmonella quality control samples in matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) identification of Salmonella in milk-containing formula foods for special medical purposes, this experiment evaluated the uniformity and stability of the quality control samples. After being stored at 20 ℃ for 0, 14 and 28 days, these samples were identified by mass spectrometry and the VITEK automatic microbial analysis system. The results showed that the quality control samples had good stability and uniformity, and their mass spectra were similar to each other. The VITEK system confirmed their identity as Salmonella. In conclusion, the ready-to-use Salmonella quality control strains can be used for the detection of Salmonella in milk-containing formula foods for special medical purposes.

A rapid detection method for Salmonella in fermented milk was developed by helicase-dependent isothermal DNA amplification (HDA). In this method, the invA gene sequence of Salmonella was used as the target gene to design specific primers, and the concentrations of UvrD helicase and T4 gp32 in the reaction system were optimized to establish the optimal reaction system. The HDA method was used to directly detect Salmonella in fermented milk, and the amplification products were detected by electrophoresis to verify the specificity of this method. The results showed that the proposed method exhibited high specificity for Salmonella in fermented milk. The optimized reaction system contained 0.10 μg of UvrD helicase and 5.0 μg of T4 gp32 per 50 μL of sample. The amplification product was consistent with the designed sequence length (304 bp). The detection limit was 2.6 × 102 CFU/g. The method can meet the requirements for the rapid detection of Salmonella in fermented milk, and thanks to its high sensitivity and easy operation, it can be used as a basic method for rapid detection of Salmonella in fermented milk.