A high performance liquid chromatography (HPLC) method was established to determine the contents of three aldehydes (malondialdehyde, acrolein, and 4-hydroxyhexenal) in infant formula milk powder, and the effect of storage temperature on the content of three aldehydes in infant formula milk powder was studied. The analytical figures of merit including linearity, accuracy, recovery, detection limit and quantitation limit were determined. The external standard method was used to quantify the analytes. The results indicated that this method exhibited good linearity in the range between 0 and 40 μg with a correlation coefficient (R2) greater than 0.999, and the detection limits for malondialdehyde, acrolein, and 4-hydroxyhexenal were 0.3, 0.4, and 0.3 mg/kg, respectively. The quantitation limits were 0.8, 1.0 and 0.8 mg/kg, respectively. The average recoveries for spiked samples were in the range of 88.29%–96.87%, with relative standard deviation (RSD) less than 10%. With increasing storage temperature above 40 ℃, the contents of the three aldehydes showed an upward trend, and a significant increase was observed in the contents of malondialdehyde and acrolein. This method has the characteristics of rapidity, high accuracy, and good reproducibility, which is suitable for the determination of the three aldehydes in infant formula milk powder.

A high performance liquid chromatography method was established to determine the content of cyromazine and its metabolite melamine in milk. The external standard method was used to quantify figures of merit such as linear relationship, precision, recovery, detection limit, and quantification limit. The results showed that the method had good linearity in the concentration range of 0.0–1.0 mg/L (R2 > 0.999), with detection limits of 0.003 and 0.004 mg/kg and quantification limits of 0.008 and 0.010 mg/kg for cyromazine and melamine, respectively. The average spiked recoveries were in the range of 84.4% to 89.5% and 83.9% to 91.2% for cyromazine and melamine, respectively, with relative standard deviations (RSDs) less than 10%. This method is characterized by high sensitivity, high accuracy, and good reproducibility, and can meet the requirement of the determination of cyromazine and its metabolite melamine in milk.

A method for the determination of phytol enantiomers in plant-based dairy products was established by gas chromatography-mass spectrometry (GC-MS). The pretreatment process was optimized, and the figures of merit of the proposed method such as linear relationship, precision, spiked recovery, limit of detection (LOD) and limit of quantitation (LOQ) were investigated. Results showed that in the concentration range of 0.0–1.0 μg/mL, the linearity of the method was good (r > 0.999). The LODs of E- and Z-phytanol were 0.03 and 0.04 mg/kg, respectively, and the respective LOQs were 0.09 and 0.10 mg/kg. The recoveries of E- and Z-phytanol in spiked samples were 78.6%–93.5% and 79.5%–94.7%, respectively with relative standard deviations (RSDs) less than 10%. This method is sensitive, accurate and repeatable, and can be used for the determination of phytol enantiomers in plant-based dairy products.

An analytical method for the determination of ethyl carbamate in fermented milk was established by gas chromatography-mass spectrometry (GC-MS). Sample pretreatment conditions were optimized. The analytical figures of merit of the proposed method including linear relationship, precision, spiked recovery, detection limit and quantitation limit were evaluated. Ethyl carbamate was quantitated using an external standard. The linearity of this method was good in the range of 0–200 ng/mL (r > 0.999), and the detection limit and quantitation limit of ethyl carbamate were 2.0 and 5.0 μg/kg, respectively. The recovery of the added ethyl carbamate ranged from 89.9% to 105.2%, with relative standard deviation (RSD) less than 10%. This method is sensitive, accurate and repeatable, and can meet the requirements for the determination of ethyl carbamate in fermented milk.

The monosaccharide composition and antioxidant activity of extracellular polysaccharides from Lactobacillus plantarum were analyzed. Crude polysaccharides were obtained from the fermentation broth of Lactobacillus plantarum by water extraction and alcohol precipitation and were fractionated into two fractions (DZ-1 and DZ-2) by DEAE-52 cellulose column chromatography. The monosaccharide components of DZ-1 and DZ-2 were analyzed by gas chromatography, and their antioxidant activity was tested using 1,1-diphenyl-2-picrylhy drazyl (DPPH), hydroxyl radical, and 2,2’-diazo bis-3-ethyl benzothiazoline-6-sulfonic acid (ABTS) cation radical scavenging assays. DZ-1 was a homopolysaccharide composed of only glucose units, while DZ-2 was a heteropolysaccharide composed of arabinose and galactose with a content ratio of 46.03:53.89. Both DZ-1 and DZ-2 had the ability to scavenge DPPH, hydroxyl and ABTS cation radicals.

To quickly and accurately evaluate the risk of ochratoxin A (OTA) pollution in dairy products, a method to detect fungi capable of producing OTA in dairy products was developed using gene probe scanning technology. According to the elucidated biosynthesis pathway of OTA, the halogenase gene related to OTA production was selected to design degenerate primers to establish a polymerase chain reaction (PCR) method for the detection of OTA-producing fungi. One OTAproducing strain (Aspergillus ochraceus) and five strains not able to produce OTA (Aspergillus cristatus, Aspergillus flavus, Fusarium moniliforme, Issatchenkia terricola, and Saccharomyces cerevisiae) were selected to test the PCR method. It was found that DNA from the OTA-producing strain but not the non-OTA producers could be amplified by PCR. Moreover, this method had high accuracy and sensitivity for detecting polluted dairy products.

A high performance liquid chromatography (HPLC) method was established for the simultaneous determination of the contents of three fumonisins in infant formula. Under optimized experimental conditions, the fumonisins were quantified by an external standard method. The analytical figures of merit such as linear relationship, recovery, precision, limit of detection and limit of quantitation of the method were examined. The results showed that the linearity of the method was good in a certain concentration range (r > 0.999). The detection limits of fumonisin B1, B2 and B3 were 10, 5, and 5 μg/kg, respectively. The limits of quantitation were 30, 15 and 15 μg/kg, respectively. The average recoveries of the fumonisins were 91.6% –95.7%, 89.5%–94.4% and 88.6%–92.3% at three different spiked levels, respectively, and the relative standard deviations (RSDs) for precision were less than 10%.

An analytical method was established by gas chromatography-mass spectrometry (GC-MS) for the simultaneous determination of the contents of 16 polycyclic aromatic hydrocarbons (PAHs) in infant formula. This method was applied to survey the levels of PAHs pollution of 45 infant formula samples sold online. The sample pretreatment procedure was optimized and the figures of merit of the method including linearity, precision and spiked recovery were examined. The external standard method was used for quantitation. The linearity of the method was good in the concentration range of 1–100 ng/ mL (r > 0.999), and the limit of detection (LOD) was 0.01–0.10 μg/ kg. The average recoveries at spiked concentration levels of 5, 10 and 50 μg/kg were in the range of 76.2%–103.1%, and the relative standard deviation (RSD) for precision was less than 10%. The detection rate of PAHs was 86.7% from 15 infant formula samples for babies of 0–6 months at levels of 0–1.12 μg/kg. The detection rate of PAHs was 80.0% from 15 infant formula samples for babies of 6–12 months at levels of 0–0.75 μg/kg. The detection rate of PAHs was 60% from 15 infant formula samples for babies of 12–36 months at levels of 0–0.60 μg/kg.

A method for the quantitation of formaldehyde in infant formula was established by gas chromatography (GC) and validated by gas chromatography-mass spectrometry (GC-MS). The level of formaldehyde pollution in 45 commercial infant formula samples was determined by the proposed method and the risk of dietary exposure to formaldehyde through the consumption of infant formula was evaluated. The sample pretreatment conditions were optimized and the analytical method was assessed in terms of linearity, precision, accuracy, limit of detection (LOD) and limit of quantitation (LOQ). Quantitation was performed using the external standard method. The results showed that the linearity of this method was good in the range of 0–10 μg (r > 0.999), the LOD was 0.1 mg/kg, and the LOQ was 0.3 mg/kg. The average recoveries at spiked levels of 0.3, 0.6 and 3.0 mg/kg were in the range of 88.33%–96.56%, with relative standard deviation (RSD) less than 10%. The formaldehyde content increased with increasing reconstitution temperature above 40 ℃. In order to simulate the actual consumption process, the infant formula samples were detected after being reconstituted with warm water at 40 ℃. It turned out that formaldehyde was found in all samples at levels of 0.38–2.72 mg/kg. The average formaldehyde exposure of infants of different ages was 20.40 μg/kg at 0–6 months, 21.11 μg/kg at 6–12 months and 26.74 μg/kg at 12–36 months.