In this study, 30 strains of S. cerevisiae were examined by in vitro gastrointestinal transit, bile salt tolerance and microbial inhibition tests to screen strains having potential probiotic properties and a symbiotic relationship with Lactobacillus plantarum IMAU10120 from them. The results showed that S. cerevisiae IMAU6Y047, IMAU7Y006, IMAU7Y007 and IMAU7Y036 were bile salt-tolerant strains and had a high survival rate over 50% during gastrointestinal transit. They were also resistant to E. coli O157, Salmonella typhimurium and Shigella flexneri. In addition, IMAU7Y006 had mutualism relationship with Lactobacillus plantarum IMAU10120. This study may provide basic data for further study on mixed-strain fermentation.

The impact of mixed starters consisting of Streptococcus thermophilus PZST4 and Lactobacillus bulgaricus PZLB5 in different proportions on the fermentation period of fermented milk and its acidity, texture, syneresis and flavor during storage was investigated. The results showed that viable cell ratios between Streptococcus thermophilus PZST4 and Lactobacillus bulgaricus PZLB5 had a striking effect on the quality of fermented milk, and a ratio of 50000:1 was the optimal combination based on the quality parameters tested.