Abstract: Lactobacillus casei J1, capable of producing bile salt hydrolase, Streptococcus thermophilus Tx and Lactococcus lactis subsp. lactis P5 that were isolated from Tibetan Kefir, were used to explore the effect of fermentation conditions and growth factors on total viable count of lactic acid bacteria and ratio between Lactococcus and Lactobacillus. Meanwhile, key batch fermentation conditions were optimized by orthogonal array design method in a 5 L automatic fermentor. The results showed that the optimal fermentation conditions were fermentation 40 ℃ for 6 h in a medium at pH 6.5 added with carrot juice as growth factor at 5%. Under these fermentation conditions, the highest total viable count of lactic acid bacteria, 6.7 × 109 CFU/mL was obtained, which revealed an approximately 70-fold increase compared to pre-optimization.

Key words: lactic acid bacteria, compound starter culture, fermentation, conditions optimization