Molecular identification and investigation of industrial importance of streptococcus thermophilus and lactobacillus delbrueckii subsp. bulgaricus isolates isolated from traditional yoghurts

Yogurt is one of the most consumed dairy product in Turkey and all over the world. Yogurt starter cultures S. thermophilus and L. bulgaricus is responsible for yogurt production. Commercial yogurt starter cultures are used for the yogurt production at industrial level. In traditional production, autochthonous cultures are used for the yogurt production although the number of autochthonous cultures is decreasing due to the domination of the commercial starters which also results in the decrement of the variation in the characteristics of yogurt. In this respect, isolation and identification of autochthonous starter cultures that can be used for industrial purposes is a crucial task. This thesis is aimed to evaluate the potential of autochthonous starter cultures to be used for industrial purposes. For this aim, traditional yogurts were collected from 10 different regions of Turkey. Specific mediums were used to isolate both starter cultures from yogurt samples and isolated were tested for their morphology and Gram stain which was followed by the test of yogurt starters by PCR reactions. The pre-typing of the isolated were conducted by RAPD-PCR analysis and S. thermophilus and L. bulgaricus strains were identified by 16S rRNA sequencing. MLST analysis was applied for the molecular typing of the strains and distinct isolated were selected for further studies. In total 44 S. thermophilus and 31 L. bulgaricus strains were tested for their technological characteristics in terms of lactic acid production level %, pH development characteristics, proteolytic activities, resistance to certain bacteriophages and EPS production characteristics and strains that revealed good characteristics were determined. Among these strains, 11 S. thermophilus and 19 L. bulgaricus strains revealed important characteristics to be used as starter cultures at industrial level.