Starter culture used in yoghurt processing is normally a mixture of Lactobacillus delbrueckii su.bulgaricus (known as Lactobacillus bulgaricus ) and Streptococcus salivarius su.thermophilus (known as Streptococcus thermopiles ). It is known that more rapid acid development is observed in mixed cultures of two bacteria than in the single strain cultures due to a symbiotic relationship between these two species of bacteria. Lactobacillus bulgaricus is a gram-positive, thermophilic microorganism used in the production of numerous dairy products, including Swiss cheese, Mozzarella cheese and yoghurt. This bacterium contributes to fast lactic acid development in yoghurt and also to its flavour and textural properties. Naturally, bacteria isolated from Iranian yoghurts are better adapted to climate of Iran and their products are perfectly matched to taste of Iranian customers. The aim of present study was to isolate, identify and characterize Lactobacillus bulgaricus from Iranian local yoghurts and then assess their potential to be used in dairy industries as yoghurt starters. Sixty one yoghurt samples from rural area from 15 provinces, mainly Isfahan , were collected and transferred to biotechnology laboratory. Isolates were identified to species level using morphological and biochemical tests including gram-staining, catalase, spore formation, growth of isolates in different temperatures and in the presence of different concentration of NaCl and fermentation of different sugars. CR molecular method was preformed aiming for more accurate identification of isolates to sub-species level using primer pair of LB1:5?-AAAAATGAAGTTGTTTAAAGTAGGTA-3? and LLB: 5?-AAGTCTCCTGGCTGG-3?. In total 72 out of 102 isolates characterized as Lactobacillus delbrueckii su.bulgaricus and their potential to be used as starter in yoghurt processing were compared with 5 commercial strains purchased from CHR Hansen and Wisby manufactures. For assessment of potential of local starters to produce acid, Skim-milk (10%) was inoculated by microbial suspension with OD 650 =1 and incubated at 42°C for 5h, pH of samples were measured in 30 min intervals. Standard loop test was carried out to determine the ability if different isolates to produce EPS. To compare the performance of the local isolates
