Formulation of Culture Medium for the Enumeration of Lactic Streptococci and Lactobacilli from Fermented Milk Products

Aims: The present study is focused to formulate a single selective differential medium for the enumeration of mixed lactic flora such as lactic streptococci and lactobacilli in domestic and market fermented milk products.

Study Design: In order to enumerate lactic streptococci and lactobacilli in a mixed flora of fermented milk, formulation of single selective medium was optimized using inhibitors and indicator instead of separate selective medium for lactic streptococci and lactobacilli.

Place and Duration of Study: The present study was conducted in the Department of dairy Microbiology, Dairy Science College, Karnataka Veterinary, Animal and Fisheries Sciences University (KVAFSU), Hebbal, Bengaluru-24, Karnataka from February 2020 to February 2021.

Methodology: Fermented milk samples like curd, yoghurt were collected, serially diluted and pour plated using Readymade M17 and MRS agar media and formulated selective yeast glucose agar medium. Lactic colonies obtained were enumerated, expressed as log10cfu/g and critical difference was calculated to declare significance and non-significance among the microbial parameters.

Results: Readymade M17 and MRS agar media gave better recovery of viable cells of lactic streptococci and lactobacilli from market samples of curd, yoghurt and domestic curd samples. The study helped to convert a general purpose medium yeast glucose agar as selective differential medium with addition of calcium propionate of 0.8 per cent to avoid Bacillus spore formers and sodium benzoate of 1.2 per cent to inhibit yeast, the common contaminants in fermented milk with 0.05 per cent BCP that led to formation of purple colonies of lactic streptococci and yellow colonies of lactobacilli.

Conclusion: The selective yeast glucose agar with 0.8 per cent and sodium benzoate of 1.2 per cent with 0.05 per cent BCP with purple colonies of lactic streptococci and yellow colonies of lactobacilli can be successfully used. This study verified the enumeration of mixed lactic flora in fermented milk products instead of M17 medium for lactic streptococci and MRS for lactobacilli, separately.