Optimization of Co-Culture Condition for <i>Lactobacillus delbrueckii</i> subsp. <i>bulgaricus</i> with Weak Post-Acidification Ability and <i>Streptococcus thermophilus</i>

To obtain high quality yoghurt starter with low post-acidification, the characteristics of mixed fermentation of yoghurt strains were studied. Lactobacillus delbrueckii subsp. bulgaricus KLDS 1.9201-11 with reduced post-acidification and Streptococcus thermophilus KLDS 3.9210 were cultivated in 2.5L fermenter with different culture temperature, initial pH and proportion of inoculums, and of which reproductive activity and ratio of viable cell count were compared. It was beneficial for the balance of final ratio of viable cell count between starter strains at the end of fermentation, when grew at 42°C, pH6.2, and the proportion of inoculums of Lactobacillus delbrueckii subsp. bulgaricus KLDS 1.9201-11 and Streptococcus thermophilus KLDS 3.9210 was 2 to 1. These results showed that different culture conditions could affect symbiotic growth of yoghurt strains, and different growth mode was an important prerequisite for collaboration growth of mixed strain and acquisition of yoghurt starter with high quality.