Milk protein is an important source of dietary protein for humans. In the modern food industry, milk and milk protein have become essential components in various processed foods. Milk protein is one of the most common allergens, and the problem of food allergies caused by milk protein has become a topical issue in the field of food safety. With the development of the dairy industry, non-milk derived food ingredients have been introduced in various dairy products, which may interact with milk protein, altering the protein’s structure and affecting its antigenic epitopes and consequently its allergenicity. Herein, we discuss the effects of food components on milk protein allergenicity from macronutrients, micronutrients and functional activities contained in the food base, and other substances. We hope that this review can improve the scientific understanding of milk protein allergenicity in food components, guide food processing safety to reduce milk protein allergenicity, and provide a basis for food allergenicity risk assessment.

The detection of pesticide residues in dairy products is an important measure to ensure the quality and safety of dairy products. Currently, QuEChERS (quick, easy, cheap, effective, rugged, safe) is widely used as a sample pretreatment for all existing methods specified in the national standards for the detection of pesticide residues in dairy products. In this paper, we review these methods with a special focus on the principle and advantages of QuEChERS as well as its application in the detection of pesticide residues in dairy products.

In order to develop a new method to determine nitrite and nitrate in milk and milk products, some improvements were made on the ion chromatography method specified in the national standard GB 5009.33-2016 Determination of Nitrite and Nitrate in Food. Samples were extracted with ultra-pure water and added with acetic acid to precipitate proteins before being chromatographed on AS11-HC column and detected with a conductivity detector. Under the above conditions, the calibration curves for nitrite and nitrate were linear with correlation coefficients greater than 0.99. The limit of quantitation (LOQ) for nitrite and nitrate was 0.25 and 0.8 mg/kg in milk, and 1 and 5 mg/kg in milk powder, respectively. The recoveries for spiked samples of milk powder and milk were from 80% to 110%. The improved method was simple to operate and cheap with ideal recovery and high precision. It could avoid potential problems encountered in the use of the traditional method and allow for more rapid and accurate detection of low contents of nitrite and nitrate in milk and milk products.

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.

An ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method for the simultaneous quantitative determination of 21 β-agonists in milk. The samples were hydrolyzed and cleaned up a solid-phase extraction column. The analytes were separated by UPLC with an Acquity UPLC BEH C18 column (50 mm × 2.1 mm, 1.7 μm) using a gradient mobile phase consisting of 0.1% formic acid aqueous solution and methanol (10 : 90, V/V). Identification and quantification were achieved by UPLC-MS/MS with multiple reaction monitoring (MRM) under the positive ion mode The limit of quantitation of all β-agonists was 0.05 μg/kg. The average recovery varied from 61.0% to 124.3% at spiked concentration levels of 0.05, 0.10 and 0.50 μg/kg with relative standard deviations (RSDs) of 2.39%–10.66%. Our results demonstrate that the method is stable, accurate and sensitive, and can be used for the determination of the 21 β-agonists residues in milk.

Fruits and vegetables have a high nutritional value, and they, apart from still being nutritious, has a good flavor after being fermented with Lactobacillus. The present article summarizes the Lactobacillus strains used for fermenting fruits and vegetables, the probiotic effect of fruits and vegetables fermented with Lactobacillus, the quality improvements of fruits and vegetables after Lactobacillus fermentation, and reviews the current global status of Lactobacillus-fermented fruits and vegetables. In addition, the main problems existing in this field and future research directions are discussed.

This paper summarizes and compares the maximum residue limits for pyrethroid pesticides in milk products in China and several other countries. At the same time, the main factors affecting the accuracy of the determination of pyrethroid pesticide residues in dairy products, including calibration curve fitting and experimental repeatability, are determined through calculation of the measurement uncertainty. Furthermore, it can be argued that the most fundamental influencing factor is the sample pretreatment method.

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.

An ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method for the quantitative determination of salicylic acid in milk and dairy products was developed. The sample was extracted with 1% acidified acetonitrile, and then the extract was purified by solid-phase extraction (SPE) with an HLB cartridge. The separation was performed on an Acquity UPLC BEH C18 chromatographic column (50 mm × 2.1 mm, 1.7 μm）with gradient elution using 0.1% aqueous formic acid-acetonitrile as the mobile phase. The target compound was monitored under the negative ion mode with an electrospray ionization (ESI) source and quantified by external standard method. The results demonstrated that the linear range of the proposed method was from 0.5 to 50.0 ng/mL with a correlation coefficient (R2) > 0.999. The average recovery of salicylic acid in different matrixes spiked at low, medium and high levels varied from 68.3% to 111.7%, and the relative standard deviations (RSDs) of precision were between 3.3% and 15.2%. The limits of detection (LODs) were 5.0 and 10.0 μg/kg in milk and milk powder, respectively. This method can meet the requirements for the determination of different salicylic acid levels in milk and dairy products.

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.

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.

An inductively coupled plasma-optical emission spectrometry (ICP-OES) method for the determination of aluminum in baby formula was developed. The sample was digested by microwave digestion and analyzed by ICP-OES. Quantitation was performed using an external standard method. The detection limit was 0.5 mg/kg for 0.5 g of the sample digested and diluted to 25 mL. Linear relationship between emission intensity and aluminum concentration in the range of 0.01 to 50.0 μg/mL was found with a correlation coefficient (r) of 0.999 5. Average recoveries of spiked samples were between 92.2% and 107.0% with relative standard deviations (RSDs) varying from 1.43% to 2.34%. The proposed method permits efficient and accurate determination of aluminum in baby formula with wide linear range, low detection limit, good precision and high recovery and good repeatability.

In January 2013, it was reported that dicyandiamide (DCD) residues were detected in New Zealand milk and milk products, which has received worldwide concern. Therefore, the development of methods to detect dicyandiamide in milk and dairy products has become a hot topic. In this paper, we review methods used to detect dicyandiamide in milk and dairy products such as HPLC-MS/MS, UPLC-MS/MS and UFLC-MS/MS, including sample extraction and purification, chromatographic column selection, mobile phase composition optimization, mass spectrometry monitoring mode and matrix effect of samples.

In this paper we review recent applications of high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS), ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS), ultra high performance liquid chromatography coupled with high-resolution time-of-flight mass spectrometry (HRTOF-MS), and matrix assisted laser desorption ionization-Fourier transform ion cyclotron resonance mass spectrometry (MALDI-FTMS) to determine penicillin residues in milk and dairy products and their major enzymatic metabolites in vivo. This review describes recent progress in the development of sample extraction, purification, chromatographic separation and mass spectrometry detection methods for the determination of penicillin residues in dairy products.

An ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS-MS) method for simultaneous determination of dicyandiamide in feed, milk and dairy products was developed. The extraction methods for feed, milk and dairy products were studied, and this was followed by selection of an appropriate chromatographic column. Samples were extracted with acetonitrile and the extract was then cleaned up on a C18 solid-phase extraction column, frozen and certrifuged to remove protein impurities, and separated on an Acquity BEH Amide column using a mobile phase composed of acetonitrile containing 0.1% formic acid and 10 mmol/L ammonium formate solution by gradient elution. Detection was performed by positive ion electrospray ionization (ESI) in multiple reaction monitoring (MRM) mode. The proposed method had good linearity in the concentration range of 1–1 000 μg/L with correlation coefficients more than 0.995. The quantification limit for feed was the highest, 40 μg/kg. Recoveries at different spiked concentrations were 80.5%– 108.4%, with RSD less than 7.0%. This method proved to be simple, rapid and suitable for the determination of feed, milk and dairy products.

A method was developed for the determination of 20 phthatic acid esters in milk and dairy products by gas chromatography-mass spectrometry (GC-MS). Samples were extracted with n-hexane and separated on a DB-5MS capillary column (30 m × 0.25 mm, 0.25 μm). The injector temperature was 280 ℃,the interface temperature was 280 ℃, and the ion source temperature was 230 ℃. Under optimized conditions, the linear range was 0-10 μg/mL with a correlation coefficient greater than 0.9990. The average spike recovery rates were in the range of 80%-109%. The detection limits were respectively 1.0 and 0.5 mg/kg for DINP and DIDP and 0.05 mg/kg for 18 others. This method proved to be simple, rapid, sensitive, specific and accurate.

A gas chromatographic (GC) method was developed and applied to determine conjugated linoleic acid (CLA) in milk and milk powder. Fat extraction from samples and methylation were made before GC analysis. Excellent separation of c9,t11-CLA was achieved. The developed method proved to be simple, safe, accurate, reliable and reproducible.