Analysis of the complete genome sequence of Lactobacillus delbrueckii ssp. bulgaricus with post-acidification capacity and its influence on yogurt in storage

In recent years, yogurt has been one of the most pop-ular fermented dairy products and is sold worldwide. In this study, pH and titrated acid changes of 4 strains of Lactobacillus delbrueckii ssp. bulgaricus fermented milk during storage were detected. The difference between L. bulgaricus KLDS1.1011 and KLDS1.0207 was signifi-cant, with the latter exhibiting reduced acidity levels. Therefore, we determined the complete genome se-quence of the 2 strains. Then the expression of specific genes and common genes related to glucose metabo-lism and proteolysis of L. bulgaricus KLDS1.1011 and KLDS1.0207 were detected by quantitative real-time reverse-transcription PCR. Analysis indicated that the key enzymes in glycometabolism and proteolysis of L. bulgaricus KLDS1.1011 were significantly different than those of L. bulgaricus KLDS1.0207. The contents of lactose and glucose decreased during storage of L. bulgaricus fermented milk, as determined by HPLC, and the contents of lactic acid and galactose increased, with L. bulgaricus KLDS1.1011 increasing less. With skim milk as a raw material, L. bulgaricus KLDS1.1011, KLDS1.0207, and Streptococcus thermophilus S1 were used as fermentation strains to yield yogurt at 42 degrees C, and sensory evaluation was compared with yogurt fer-mented by commercial starter cultures. Yogurt from L. bulgaricus KLDS1.1011 was the highest-rated. There-fore, the study may provide guidelines for the develop-ment of yogurt starters.

Automated summary

This study investigated the pH and acid changes in fermented milk of different Lactobacillus delbrueckii ssp. bulgaricus strains during storage, and found significant differences in gene expression and chemical composition related to glucose metabolism and proteolysis between the strains. The yogurt produced with L. bulgaricus KLDS1.1011 was rated the highest in sensory evaluation, suggesting it may have potential for use as a yogurt starter culture.