In this study, headspace gas chromatography-mass spectrometry (HS-GC-MS) was used to accurately identify and quantify ethylene oxide and 2-chloroethanol in milk and dairy products (liquid milk, fermented milk, infant formula milk powder, and ice cream). The sample was diluted to a constant volume in a headspace bottle and balanced at 90 ℃ for 20 min, and the extract was separated on a DB-624 capillary column (60 m × 0.32 mm, 1.8 μm) with temperature programming. Ethylene oxide and 2-chloroethanol were detected using an electrospray ionization (ESI) source in the selected ion monitoring (SIM) mode. Quantitation was carried out using matrix-matched calibration curves. Good linearity was obtained in the range of 0.1–10.0 mg/L (R2 ≥ 0.99). The limits of detection of ethylene oxide and 2-chloropropanol in milk, fermented milk and ice cream were 0.12 and 0.60 mg/kg, respectively. At three spiked levels, the average recoveries of the two compounds were between 75.9% and 101.6%, with relative standard deviations (RSD) less than 10%. This method is precise and accurate, and can meet the requirements for the detection of milk and dairy products with a complex matrix.

According to acid production rate, tolerance to pH 2.5 artificial gastric juice, pH 8.0 artificial intestinal juice and 0.3% bile salt, 11 with significantly higher acid production rate (P ＜ 0.05) were screened from 298 strians of Lactobacillus casei isolated from traditional fermented dairy products and among them, IMAU60143, IMAU70020 and IMAU10510 had excellent tolerance to artificial gastric juice and bile salt (P ＜ 0.05) and good storage stability in brown active dairy beverages. IMAU70020 remained greater than 5.0 × 108 CFU/g after 28 days of storage at 4 ℃.