A new method for detecting five aflatoxin residues in raw milk was presented using micellar electrokinetic capillary chromatography with a diode array detector (MECC-DAD). The specificity of MECC-DAD was evaluated in comparison with that of high-performance liquid chromatography with a fluorescence detector (HPLC-FLD). In the MECC-DAD method, samples were cleaned up by immunoaffinity column chromatography before separation on an uncoated fused-silica capillary column using 7.5 mmol/L borate buffer with 30 mmol/L sodium dodecyl sulfonate (pH 8.5) and 5% acetonitrile and the detection wavelength was set at 214 nm. In the HPLC-FLD method, samples were separated on a C18 column (150 mm × 4.6 mm, 5 μm) by gradient elution using a mobile phase consisting of acetonitrile and water after being cleaned up by immunoaffinity column chromatography. The analytes were detected by a fluorescence detector at 360 nm excitation wavelength and 440 nm emission wavelength. Results showed that MECC-DAD gave smoother and sharper peaks that were more symmetrical without tailing. The limits of detection of MECC-DAD and HPLC-FLD were 0.182–1.669 and 0.014–0.058 μg/L, both meeting the requirements for the determination of aflatoxin residues in raw milk. The precision of HPLC-FLD was somewhat higher than that of MECC-DAD. The recoveries of MECC-DAD and HPLC-FLD were 80.3%–137.0% and 79.6%–134.0%, respectively. When the two methods were applied to the same commercial milk samples, the P value for the deviation between the quantitative results obtained was 0.900, greater than 0.05, indicating no significant difference. In conclusion, MECC-DAD was simple, efficient and inexpensive, making it more suitable for the simultaneous determination of five aflatoxins in milk than HPLC-FLD.

The probiotic Lactobacillus plantarum LIP-1 was cultured in modified MRS medium at high cell density to investigate the effect of changes in medium components (the types and amounts of nitrogen source, carbon source and buffer salt, total amount of carbon and nitrogen, and carbon/nitrogen ratio) on the viable cell count and survival rate after freezedrying of this strain. The optimal medium was found to be composed of carbon source (sucrose) 33.35 g/L, nitrogen source (yeast powder, soy peptone and casein peptone, 3:3:5, m/m) 10.80 g/L, and buffer salt (sodium acetate, potassium dihydrogen phosphate and sodium citrate, 2.5:1:1, m/m) 14.85 g/L (namely 0.13 mol/L). The viable cell count of strain LIP-1 cultured in the optimized medium after freeze-drying was 9.767 (lg(CFU/mL)), which was distinctly higher than that cultured in MRS medium. The modified medium allowed high-cell-density fermentation of Lactobacillus plantarum LIP-1 while maintaining its viability during freeze-drying.