This study aimed to select and optimize a sample extraction method for the determination of nitrite from milk powder. The absorbance of the experimental water stored for different periods of time was detected by three extraction methods, heat extraction, ultrasonic extraction and ultrasonic decolorization. The color and spiked recoveries of the filtrates from the three methods were evaluated. The nitrite content of quality control samples was determined by ultrasonic decolorization and the limit of detection (LOD) of this method was investigated. The results indicated that storage time did not affect the absorbance of the experimental water. The recoveries of the ultrasonic decolorization method were over 90%, with relative standard deviations (RSD) less than 10%. and the measured results of the quality control samples were within the characteristic value range with LOD of 0.4 mg/kg, which meets the laboratory quality control requirements. The ultrasonic decolorization method has good accuracy and accuracy, and it is recommended that it be used for the decolorization of colored substances in the national standard method.

A liquid chromatographic (LC) method was established for the determination of α-casein, β-casein, κ-casein, α-lactalbumin and β-lactoglobulin in ultra high temperature (UHT) milk. The proteins in milk were denatured by adding a buffer solution containing bis[tris(hydroxymethyl)aminomethane (BisTris), guanidine hydrochloride, sodium citrate, dithiothreitol, etc. The analytes were detected by an ultraviolet (UV) detector and quantified by the external standard method. The results showed that the calibration curve of each protein had good linearity with a correlation coefficient above 0.995. The recoveries of spiked samples were between 95.2% and 105.0%, the detection limit was 0.01–0.02 g/100 mL, and the relative standard deviation was 0.78%–2.70%. The method is characterized by good separation effect, good repeatability and simple operation, and is suitable for quantitative analysis of α-casein, β-casein, κ-casein, α-lactalbumin and β-lactoglobulin in UHT milk.

In this study, the complete antigens of fipronil and its analogue were synthesized using glutaraldehyde (GA) and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) as a cross-linker, respectively, and were identified by ultraviolet absorption spectroscopy and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). BALB/c mice were immunized with fipronil-bovine serum albumen to obtain hybridoma cell 3F6. Monoclonal antibodies were prepared by inducing ascites in mice. An enzyme-linked immunosorbent assay (ELISA) was developed and evaluated to determine fipronil in milk. The results showed that the concentration of the prepared monoclonal antibody, belonging to the IgG1 subclass, was 8.5 mg/mL, and the titer was 2.0 × 106. The cross-reaction rates with fipronil-desulfinyl, fipronil sulfone and fipronil sulfoxide were 9.21%, 14.02% and 21.46%, respectively. The recoveries of fipronil in spiked milk were 87%–118%, and the coefficient of variation for precision was less than 15%. In conclusion, this method is highly accurate and precise.

The purpose of this study was to investigate the factors affecting somatic cell counts (SCC) and milk composition of Chinese Holstein cows in Ningxia. The correlation of 198 855 measurements of the dairy herd improvement (DHI) data of 19 020 Chinese Holstein dairy cows (from 2009 to 2018) from 7 different dairy farms was analyzed using Minitab software. The results showed that 1) SCC was significantly correlated with farm, year and parity (P < 0.05); 2) SCC fluctuated with season and calving month, and decreased first and then increased with increasing lactation length; and 3) there were significant correlations between SCC and milk yield, milk fat percentage, milk protein percentage, milk sugar percentage and dry matter percentage (P < 0.05). Moreover, SSC, milk yield and the major milk components were influenced by environmental factors (farm, year and season) and cow’s own factors (parity, calving season and lactation period). In summary, fine management is an effective avenue to improve milk production and quality.

A helicase-dependent isothermal DNA amplification (HDA) assay was developed for the rapid and accurate detection of Gluconacetobacter in yogurt.A pair of specific oligonucleotide primers according to the 16S ribosomal RNA gene (GenBank accession number:HQ677466.1) of Gluconacetobacter was designed,and the optimal concentration of UvrD helicase and T4 gp32 in the reaction system were determined.The HAD method enabled direct detection of Gluconacetobacter in yogurt.The specificity of the method was tested by amplification and electrophoresis of various strains in yoghurt using the HAD system.The amplification product by HDA was the same as the designed gene fragment (101 bp).The sensitivity of HDA was 102 CFU/g.The optimal reaction system was established by the use of 0.1 μg of UvrD helicase and 5.0 μg of T4 gp32.In conclusion,the method was sensitive and time saving.