A reversed-phase high performance liquid chromatography (RP-HPLC) method was established for the determination of 6S-5-methyltetrahydrofolate calcium in milk powder. After protein precipitation with trichloroacetic acid solution, samples were extracted with ascorbic acid solution in a hot water bath, and the extract was separated on a C18 reversed-phase column by gradient elution using a mobile phase composed of 0.1% trifluoroacetic acid solution and methanol, and the detection wavelength was set at 280 nm. Quantitative analysis was carried out by the single standard method. The results showed that the limit of quantification and detection of 6S-5-methyltetrahydrofolate calcium in milk powder samples were 150 and 50 μg/100 g, respectively. The recoveries for samples spiked at levels ranging from 150 to 600 μg/100 g were 95.0%–109.1% with relative standard deviations (RSDs) between 1.26% and 4.04%. This method is simple, accurate, with high recovery and reproducibility, and suitable for the determination of 6S-5-methyltetrahydrofolate calcium in milk powder.

Being rich in nutrients, dairy products provide a good environment for the growth of Staphylococcus aureus, Salmonella, Listeria monocytogenes, Cronobacter and other foodborne pathogens, which poses a serious threat to the safety of dairy products. Therefore, rapid and accurate detection of foodborne pathogens in dairy products is essential to the prevention of foodborne pathogens. In recent years, analytical techniques including molecular biology and immunoassays have rapidly developed and attracted much attention due to their advantages of high sensitivity, rapidity and simplicity compared with the traditional food pathogen detection methods, which are cumbersome and time-consuming. In this paper, recent developments and applications of foodborne pathogen detection techniques are reviewed, and future trends were discussed in order to provide a reference for the rapid detection of foodborne pathogens in dairy products.

A reversed-phase high performance liquid chromatographic (HPLC) method was established for the determination of erythrosine in fermented milk. After enzymatic hydrolysis, the sample was extracted with anhydrous ethanol, and purified by solid phase extraction using an HLB column under alkaline conditions. The separation was performed on a C18 reversephase column by gradient elution using a mobile phase comprising 20 mmol/L ammonium acetate buffer solution (pH 6.5) and methanol. The detection wavelength was set at 520 nm, and quantification was performed by the external standard method. The results showed that the linear range for erythrosine was 0.05–20.00 μg/mL. The limit of quantitation (LOQ) and the limit of detection (LOD) of erythrosine in fermented milk samples were 0.2 and 0.1 mg/kg, respectively. The recoveries from fermented milk samples spiked at levels of 0.2–2.0 mg/kg were 96.5%–105.6%, and the relative standard deviations (RSD) were 1.87%–2.21%. The method is simple and accurate, has high recovery and good repeatability, and is suitable for the determination of erythrosine in fermented milk.

The measurement uncertainty was estimated for the determination of 1-oleic-2-palmitic-3-linoleic acid triglyceride (OPL) content in milk powder by gas chromatography (GC). According to the Measurement and Expression of Uncertainty in Measurement (JJF 1059.1—2012) and the Guidance on Quantifying Uncertainty in Chemical Analysis (CNAS-GL 006: 2019), a mathematical model was established to analyze the sources of measurement uncertainty. The major factors affecting the measurement uncertainty were evaluated. Results showed that the average OPL content of six milk powder samples was measured to be 1.172 g/100 g. The relative expanded uncertainty (urel) was 0.023 6 with a coverage probability of approximately 95%. The standard uncertainty arising from sample preparation was the main source of uncertainty.

A small amount of bacterial spores with strong tolerance still exist in raw milk after sterilization and can multiply under certain conditions, causing a serious impact on product quality and consumer health. In this study, raw milk samples containing Bacillus were collected to isolate aerobic Bacillus and thermophilic aerobic Bacillus. The isolates obtained were identified based on their morphological, physiological, biochemical and molecular biological characteristics, and the heat resistance of the isolated thermophilic aerobic Bacillus was studied. Results showed that 10 strains of Bacillus were isolated from the milk samples, of which three were thermophilic aerobic Bacillus and seven were aerobic Bacillus. Among them, Bacillus coagulans and Bacillus clausii could tolerate heat treatment at 115 ℃ for 15 min. All Bacillus in raw milk could be killed by heat treatment at 121 ℃ for 20 min which decreased the number of spores by four orders of magnitude. The dominant Bacillus species in raw milk were Bacillus subtilis, Bacillus cereus, Bacillus pumilus, Bacillus licheniformis, Bacillus circulans, Bacillus gelatini, Bacillus amyloliquefaciens, Bacillus coagulans, and Bacillus clausii. Bacillus coagulans and Bacillus clausii had stronger heat resistance and could tolerate heat treatment at 115 ℃ for 15 min.

A high performance liquid chromatographic (HPLC) method was developed for the determination of naringin in milk and dairy products. Samples were extracted with methanol, and the analytes were separated on a C18 column using a mobile phase consisting of 0.1% acetic acid aqueous solution and acetonitrile (75:25, V/V), detected by a diode array detector at 284 nm and quantified by an external standard method. The results showed that the linearity of this method was good in the concentration range of 5–500 μg/mL with a correlation coefficient of 0.999 9. The recoveries of powdered and liquid milk power and yogurt spiked at 0.02, 0.04, and 0.08 g/100 g were 96.2%–103.2%, 96.3%–103.7%, and 99.7%–104.1%, respectively, with relative standard deviations (n = 6) of 1.12%–2.31%, 1.25%–1.85%, and 1.24%–1.66%, respectively. The reported method is simple, rapid, accurate, repeatable, and suitable for the determination of naringin in milk and dairy products.

Dairy products are favored by more and more consumers because of their rich nutrients and good taste, and have become an important part of consumers’ dietary structure. At the same time, the food safety of dairy products has become the focus of consumers’ attention. Therefore, controlling dairy food safety is a top priority for every dairy company. This article expounds on the food safety control measures for ensuring quality and safety in each link of the dairy product production process. To ensure the safety of milk sources, pasture construction and management and risk control during breeding activities need to be considered. The control of raw and auxiliary materials needs to be carried out by considering the acceptance system, storage of raw and auxiliary materials, and upstream supplier management and control. The control of the production process needs to be carried out from the aspects of personnel, equipment, ingredient and environmental management. In addition, this review highlights the importance of big data technology in dairy food safety risk analysis. We expect that this review will be helpful to relevant enterprises in improving their work on food safety management.

A gas chromatographic (GC) method for the determination of 1-oleic-2-palmitic-3-linoleic-triglyceride (OPL) in milk powder was established. The samples were extracted with ether and petroleum ether, and the extract was concentrated to near dryness, re-dissolved in n-heptane, separated on a CP-TAP CB elastic quartz capillary column, detected by a hydrogen flame ionization detector, and quantified by an external standard method. The column temperature was programmed to rise. The inlet temperature was set at 330 ℃. The samples (1.0 μL) were injected using the split mode (1:10). The detector temperature was set at 360 ℃. Nitrogen was used as the carrier gas. The makeup flow rate (nitrogen) was 25 mL/min. The recovery of OPL from spiked milk powder at 1–6 g/100 g ranged from 95.2% to 101.9%, and the relative standard deviations (RSDs) for precision ranged from 1.289% to 1.998%. The limit of detection (LOD) and limit of quantitation (LOQ) of the proposed method were 0.2 and 1.0 g/100 g, respectively. This method, therefore, is simple, accurate, repeatable, and suitable for the determination of OPL in milk powder.

Inductively coupled plasma-mass spectrometry (ICP-MS) was used to measure the aluminum content in the quality control sample of milk powder, and an X-control chart was established for runaway judgement and handling during the operation process. The precision and median line of the control chart for new data points obtained one year later were evaluated using Minitab software with test for equal variance and analysis of variance. The standard deviation for the previous 25 data points was 0.186 mg/kg compared to 0.126 mg/kg for the 35 new ones, while the median values of the two groups did not differ from each other. More reliable control limit was calculated based on all the data points, and the new median value was 1.334 mg/kg with a standard deviation of 0.154 mg/kg. The decrease in standard deviation suggested that the precision was improved with smaller data fluctuations. In conclusion, calculation of new and more reliable control limit from more data is useful to find obvious systematic errors, abnormal data and slow changing trend in a timely and effective way and can provide evidence to decide whether data should be retained or removed so as to directly reflect the stability and tendency of the detection.

A gas chromatographic (GC) method to determine the contents of 16 trans fatty acids in ice cream was established. The 2.0 g samples were pretreated sequentially with 8 mL of hydrochloric acid and 10 mL of anhydrous ethanol, separated on an SP-2560 capillary column, detected by GC with a flame ionization detector (FID) and quantified by the peak area normalization method. Under optimized chromatographic conditions, the limit of detection and limit of quantification of the proposed method were 0.012% and 0.024%, respectively, and it allowed effective separation of trans fatty acid methyl esters from cis fatty acid methyl esters and saturated fatty acid methyl esters.

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.

A method for the determination of zeaxanthin in milk powder was developed using high performance liquid chromatography (HPLC). The sample was saponified with potassium hydroxide solution to release zeaxanthin, extracted with a mixed solvent of ethyl ether, n-hexane and cyclohexane and frozen for degreasing. The chromatographic separation was performed on a C30 column with gradient elution. The analyte was detected with an ultraviolet detector and quantified by an external standard method. The limit of quantification was 100 μg/100 g and the limit of detection was 30 μg/100 g for zeaxanthin in milk powder. The method recoveries at spiked concentration levels of 90–811 μg/100 g were 85.8%–102.2%, with relative standard deviations ranging from 1.43% to 2.76%. This method was accurate, repeatable, precise and sensitive.

By analyzing some factors involved in the determination of lead in milk powder by inductively coupled plasma mass spectrometry (ICP-MS) such as containers and reagents used, an ultrasonic cleaning method was established to effectively reduce the blank value. The method gave a detection limit of 0.005 mg/kg, which was much lower than that (0.02 mg/kg) of traditional methods. The recoveries of samples spiked at concentration levels of 0.005–0.015 mg/kg ranged from 86.9% to 119.0% with relative standard deviations (RSDs) of 3.1%–12.3%, meeting the requirements for methodological validation. Hence, the method proved to be overall feasible and suitable for the detection of lead in milk powder with reduced detection limit.

A reversed-phase high performance liquid chromatography (RP-HPLC) method for the simultaneous quantitative determination of vanillin, methyl vanillin, ethyl vanillin and coumarin in milk and dairy products has been established. Vanillin compounds from samples were extracted with acetonitrile, blown to dryness under nitrogen, and then cleaned up with n-hexane. The chromatographic separation was achieved using a mixture of 20 mmoL/L ammonium acetate (pH 5.6), acetonitrile and methanol as the mobile phase with gradient elution on a C18 column. The analysis was carried out using a UV detector at a wavelength of 267 nm and the analytes were quantified by an external standard method. Good linear relationships in the range of 0.05–5.00 μg/mL were observed for all analytes. The limit of quantification was 0.2 mg/kg and the limit of detection was 0.06 mg/kg for the four analytes in liquid milk, milk powder, yogurt, lactic acid fermented beverage, ice cream, and cheese. The recoveries for vanillin, methyl vanillin, ethyl vanillin and coumarin in these samples at spiked concentration levels of 0.2–2.0 mg/kg were 80.6%–110.0%, 80.1%–109.6%, 80.4%–109.5% and 80.1%–105.9%, with relative standard deviations of 1.87%–7.70%, 1.45%–9.80%, 1.66%–9.52% and 1.16%–9.52%, respectively. This method was rapid, accurate, repeatable and simple and could be applied to determine vanillin compounds in milk and dairy products.

The residues of ochratoxin A, deoxynivalenol, aflatoxins B1 and zearalenone in dairy feeds were simultaneously detected using biochip array technology. The method accuracy, precision and reproducibility were evaluated. The results obtained that the correlation coefficient of the calibration curve for each analyte was greater than 0.99. The recoveries for quality control sample and negative sample at two spiked levels varied from 80% to 120%. The coefficient of variance (CV) was less than 15% for accuracy and reproducibility and was less than 10% for reproducibility. Compared with high performance liquid chromatography, this method gave consistent results with a simpler sample pretreatment procedure. In conclusion, the biochip array method was simple and accurate and it could provide an efficient and reliable tool for mass screening of samples.

A method for the determination of lactose in low-lactose milk and lactose-free milk by using ion chromatography was developed. Lactose from samples was extracted with 3% acetic acid as a protein precipitator. The method was performed on a CarboPacTM PA20 column by gradient elution. The analyte was detected with an electrochemical detector and quantified by an external standard method. The limit of quantification was 100 mg/kg and the limit of detection was 50 mg/kg for lactose in milk. The recoveries at spiked concentration levels of 100–500 mg/kg were 92.3%–103.4%, with relative standard deviations between 1.44% and 4.43%. This method proved to be rapid, accurate, repeatable, sensitive and simple.

Enterobacterial repetitive intergenic consensus-polymerase chain reaction (ERIC-PCR) allows gene amplification using primers designed based on ERIC, which are widely present in living organisms, yielding products that are useful to characterize the genomic structure. This method has been widely used in bacterial classification and research on the genetic relationship of strains because of its merits such as simplicity, ease of implementation, good repeatability and time saving. This paper reviews the background to bacterial classification research and the principle and characteristics of ERIC-PCR technique, and summarizes the advantages and disadvantages of ERIC-PCR technique in bacterial genotyping and recent progress in its application to genotype common food-borne pathogenic bacteria. At the same time, future prospects for the application of ERIC-PCR in traceability analysis of microbial contaminants in dairy enterprises.

In this paper, an ion chromatography method for the determination of galactooligosaccharides (GOS) in milk powder was established. The protein in the sample was precipitated by acetonitrile, and GOS was extracted with acetonitrilewater and purified using a C18 column (or RP column) to remove impurities. The analyte was separated using an ion chromatograph equipped with quaternary gradient pumps and detected with a pulse amperometric detector. The calibration curve of this method had good linearity in the range of 10–300 μg/mL, and the results from repeated sample measurements were stable. The recovery rates from blank samples spiked at levels of 500–2 000 mg/100 g were 82.1%–98.0%. To sum up, this method required simple sample pretreatment and gave accurate results, and it could be suitable for the determination of the GOS content in milk powder samples.

A method for the determination of eight colorants, new red, amaranth, allura red, ponceau, tartrazime, sunset yellow, indigotine and brilliant blue in fermented milk by high performance liquid chromatography was developed. The analytes were extracted from samples with weakly alkaline water at 7.7–7.9 and cleaned up on a polyamide solid phase extraction cartridge. The analysis was performed on a C18 column with gradient elution using 0.02 mol/L sodium acetate solution-methanol as mobile phase. The results showed that the recoveries of seven colorants other than indigotine at spiked concentration levels of 0.5–5.0 mg/1 000 g in fermented milk were higher than 90%, while the recovery of indigotine was around 80%. The limit of detection of the method was 0.5 mg/kg. The repeatability relative standard deviation was less than 5%, indicating good precision. With the advantages of accurate results, simplicity and good repeatability, this method is suitable for the analysis of colorants in fermented milk.

An ultra performance liquid chromatography-tandem mass spectrometry method for the simultaneous quantitative determination of four tetracycline residues in dairy products, including milk, yogurt and milk powder, has been established. In this method, the pretreatment and instrument operating conditions were optimized. Tetracycline residues were extracted into EDTA-Mcllvaine buffer and then cleaned up by an HLB solid-phase extraction cartridge. After the residues were eluted with a mixture of methanol and acetonitrile (1:9, V/V), the eluate was blown to dryness under nitrogen. The resulting residue was then redissolved. The analysis was carried out using positive ion electrospray ionization under the multiple reaction monitoring mode. The limits of quantification were 10 μg/kg for tetracycline, oxytetracycline, chlortetracycline and doxycycline in milk powder; the limits of quantification were 2 μg/kg in milk and yogurt. The recoveries of the tetracyclines fortified at levels from 2 to 100 μg/kg ranged from 63.1% to 100.6% with relative standard deviation of 1.8%–10.7%, and the matrix effects were 100.5%–122.1%. In conclusion, this method is accurate, rapid and highly sensitive and exhibits good repeatability and wide linearity. Thus it is suitable for the determination of tetracycline antibiotic residues in milk, yogurt and milk powder.

An ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method for the simultaneous quantitative determination of fipronil and its metabolites in whole egg powder, egg yolk powder and dairy products was developed. Samples were extracted with acetonitrile and saturated sodium chloride solution was added to separate the organic and aqueous phases. The supernatant after low-temperature precipitation of protein was applied onto an HLB solid-phase extraction cartridge for purification. The chromatographic separation was accomplished with an Acquity UPLC BEH C18 column (2.1 mm × 50 mm, 1.7 μm) using gradient elution with a mobile phase consisting of a mixture of acetonitrile and water. The analytes were detected using a negative electrospray ion source under the multiple reaction monitoring mode and quantitated by the external standard method. The results demonstrated that the linear ranges were from 0.5 to 20.0 μg/L with good correlation coefficients (R2 > 0.990). The limit of detection and the limit of quantitation were 0.2 and 1.0 μg/kg for all analytes, respectively. The recoveries of fipronil and its metabolites in different matrixes at spiked concentration levels of 1, 2, 4 and 20 μg/kg varied from 63.4% to 118.7%, with relative standard deviations between 0.7% and 10.3%. The method proved to besensitive, accurate and suitable for the rapid quantification of fipronil, fipronil sulfide, fipronil sulfone and fipronil desulfinyl in protein-rich foods.

An ultra performance liquid chromatography-tandem mass spectrometry method for the simultaneous quantitative determination of four cephalosporin residues in dairy products, including milk, yogurt and milk powder, has been established. The samples were extracted with 5% formic acid acetonitrile. After being purified by solid-phase microextraction using an Oasis PRIME HLB cartridge, the extract was blown to dryness under a stream of nitrogen gas and then re-dissolved. The analysis was carried out using a positive electrospray ion source in the multiple reaction monitoring mode. The limit of quantification was 32 μg/kg for cefalexin, cefapirin, cefalonium and cefquinome?in milk powder; the limit of quantification was 4 μg/kg in milk and yogurt. The recoveries at spiked concentration levels of 4-150 μg/kg were 63.3%-112.1%, with relative standard deviations of 1.6%-10.5%. The matrix effects were 108.77%-379.91%. This method was characterized by short analysis time and was suitable for the determination of cephalosporin residues in different dairy products.

An ultra performance liquid chromatography-tandem mass spectrometry method for simultaneous quantitative determination of four quaternary ammonium compounds in dairy products, including milk, yogurt and milk powder, has been established. Quaternary ammonium compounds from samples were extracted with methanol and cleaned up by solid phase extraction using a weak cationic exchange reversed-phase adsorbent (WCX). The chromatographic separation was achieved using a mixture of formic acid and methanol (2:98, V/V) as the elution solvent. The eluate was evaporated to dryness under a stream of nitrogen gas and the residue was re-dissolved prior to analysis using a positive electrospray ion source in the multiple reaction monitoring mode. The limit of quantification was 10 μg/kg for dodecyl trimethyl ammonium bromide, benzylcetyldimethyl ammonium chloride, tetradecyl dimethyl benzyl ammonium chloride and didecyl dimethyl ammonium chloride in all three dairy products. The recoveries at spiked concentration levels of 10-200 μg/kg were 81.4%-105.6%, with relative standard deviations ranging from 0.97% to 6.04%. The matrix effect was in the range of 90.89%-234.94%. This method was rapid, accurate, repeatable and was suitable for the determination of quaternary ammonium compounds in various dairy products.

A method for the determination of nonylphenol in liquid milk by using ultra high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was developed. Samples were extracted using acetonitrile as extraction solvent and the organic phase was separated from the aqueous phase by adding saturated sodium chloride solution. The analyte was cleaned up using a ProElut PAEs Glass solid-phase extraction catridge and then separated on a Waters ACQUITY UPLC BEH C18 column (2.1 mm × 50 mm, 1.7 μm) using gradient elution with 0.1% ammonia water-methanol as mobile phase. The detection was performed by negative electrospray ionization under the multiple reaction monitoring mode and the quantitation was carried out by an internal standard method. The results showed a good linear relationship (R2 > 0.990) in then range from 1 to 200 ng/mL. The limit of detection（LOD, RS/N = 3）was 2.0 μg/kg and the limit of quantitation (LOQ, RS/N = 10）was 5 μg/kg. The recovery rate of the method for spiked samples was between 74.8% and 111.5% with relative standard deviation of 3.3%-9.0%. In general, the method was accurate, simple and reproducible and exhibited low background inference and it was thus suitable for the analysis of nonylphenol in liquid milk.