Abstract:

In the present study, two yoghurt strains, Lactobacillus bulgaricus (KLDS 1.9201) and Streptococcus thermophilus (KLDS 3.0201) were cultured in 2.5-L fermentor with four initial lactose concentrations ranging from 30 to 90 g/L, and the process kinetic parameters including lactose consumption, cell number inrease and lactic acid production were investigated. The results indicated that the higher concentration of lactose had an inhibitory effect, and the initial lactose at a concentration of 50 g/L or 70 g/L was suitable. Under the former concentration, the lactose utilization rate by KLDS3.0201 reached 85.3%, the lactic acid production reached 36 g/L, and the living bacterial population was up to 4.4×109 CFU/ml after 6 h growth. Under the latter concentration, the lactose utilization rate by KLDS1.9201 reached 85.7%, the lactic acid production reached 52 g/L, and the living bacterial population was up to 2.15×109 CFU/ml after 8 h growth.

Key words: yoghurt strains, batch fermentation, initial lactose concentration