Abstract: The preliminary growth characteristics of three mesophilic lactic acid bacteria (Streptococcus. lactis. subsp. Lactis,Streptococcus. lactis. subsp. Cremoris, Streptococcus. lactis. subsp. Diacetylactis) in MRS medium and defatted milk culture mediumwere studied. These lactic acid bacteria are often used in manufacture of Quark cheese. The results indicated that in the MRSmedium, the adaptation phase of the three lactic acid bacteria was 0～2h, and 2～8h was the logarithmic growth phase, and duringthe stationary phase, the turbidity of the three starter cultures was about 1.5 (OD600nm). The growth density doubling time duringthe logarithmic growth phase was around 1h. In the RSM medium, when the inoculation is 105 CFU/ml, the adaptation phase of thethree starter cultures was much shorter. The stationary phase was achieved by S. lactis and S. cremoris after incubation for 6h andthe maximum viable cell counts reach 1.33 × 109CFU/ml and 1.61 × 109CFU/ml respectively. After 8h’s incubation, the S.diacetylactis reaches stationary phase and the maximum viable cell counts became 7.75×108CFU/ml. In this experiment, the storestability of the three starter cultures in the RSM medium was also studied confirming the viable cell counts and the acid producingability. The results indicated that within 8d, the viable cell counts and the acid producing ability of S. lactis and S. cremoris keptstable. For S.diacetylactis, the viable cell counts kept stable within 14d, but the acid producing ability decreased after 5d’s storage.

Key words: Mesophilic Lactic Acid Bacteria, growth characteristics, generation time, store stability