Strain HY-1, isolated from raw milk, was identified as Hafnia alvei by morphological, physiological and biochemical characterization and 16S rRNA sequence analysis, and its biological properties such as resistance to antibiotic, salt, acid and alkali, swimming motility and biofilm formation capacity were evaluated. Results showed that HY-1 was resistant to a wide range of antibiotics, which was moderately susceptible to tetracycline, erythromycin, penicillin G, ceftazidime, and cefuroxime axetil, and was resistant to midecamycin, clindamycin, clarithromycin, oxacillin, cephalothin, and cefazolin. HY-1 could grow in media at pH 5.0–8.0 containing 0.2–0.5 g/mL of sodium chloride at 4–37 ℃, and showed swimming motility as evidenced by the halo on the surface of the swimming plate. In addition, HY-1 could form biofilms, and milk at 2 mg/mL had the potential to facilitate biofilm formation by HY-1 and consequently increase its transmission and contamination, which may cause food quality and safety problems. However, when the concentration of NaCl equaled or exceeded 0.4 g/mL, the biofilm formation ability of HY-1 was significantly inhibited, indicating that the transmission and contamination of HY-1 could be intercepted by appropriate concentrations of NaCl.

Significant variations in components of fresh milk with season, temperature, and milking time and frequency lead to large differences in yogurt quality. In this paper, the influence of the contents of milk protein, fat and lactose on water retention and acidity of yogurt during storage was studied. The results showed that the water-holding capacity of yoghourt stored at 4 ℃ was apparently enhanced with increasing addition of milk protein, fat and lactose contents. Moreover, the acidity of yogurt was increased significantly with increasing addition of milk protein content, but was not significantly affected by the amount of fat or lactose.