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.

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.

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.

Fermented milk was produced from fresh goat milk, blueberry juice and mulberries with added neotame and soybean oligosaccharides as sweeteners. The optimization of process parameters based on sensory evaluation, acidity and water-holding capacity was carried out using one-factor-at-a-time and orthogonal array design methods. The results showed that the optimal conditions were determined as follows: milk to blueberry juice ratio 7:3 (V/V), inoculum size 4 g/L, neotame to soybean oligosaccharide ratio 0.35:10, fermentation time 5 h, and one mulberry added to 100 mL of fermented milk. The yogurt produced under these conditions was light purple in appearance, having a uniform color embellished with purple mulberries, and it had good gelling properties and a good flavor with water holding capacity was 35%, acidity was 110 °T. Its sensory score was 95 points. The yogurt was found to contain 7.744 mg/L anthocyanidins by an ultraviolet spectrophotometric method, suggesting it to be a novel healthy goat milk product. The yogurt was determined to have potent antioxidant activity in comparison with the positive control ascorbic acid.