STUDIES ON YOGURT PRODUCTION USING Lactobacillus bulgaricus AND Streptococcus thermophilus ISOLATED FROM MARKET YOGURT

Yogurt is a fermented milk product obtained from fermentation of Lactobacillus bulgaricus and Streptococcus thermophilus strains. The aim of this study was to produce yogurt using isolated native starters Lactobacillus delbruckii sub sp. Bulgaricus and Streptococcus saliverius sub sp. thermophilus. In this study yogurt samples were collected from the local markets. The native starters were isolated, purified and identified according to Bergey’s manual of determinative bacteriology. Lactobacillus bulgaricus and Streptococcus thermophilus were screened with respect to their acid and flavour production for the preparation of a natural yogurt and compared to a commercial starter cultures. Yogurt was made by inoculating isolated bacteria (starter culture) usually Lactobacillus delbruckii subsp. bulgaricus and Streptococcus saliverius subsp. thermophilus into milk. After inoculation the mixture was incubated at 42 ° C for 6 to 8 hours and coagulation was observed and yogurt pH was measured. It is well known that yogurt production using native starter cultures instead of commercial ones is beneficial in respect of both economic and organoleptic aspects. The present results indicated that the isolated native yogurt starters can be used in yogurt manufacturing industry at a large scale.