Enumeration of Lactic streptococci from Fermented Milk Products using Differential Medium

Author: Gopal S., Yadav S., Ramachandra B. and Prabha R.

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Abstract

In order to formulate a single medium for the accurate enumeration of lactic streptococci in fermented milk products avoiding common microbial contaminants and to easily find the colonies an attempt has been made in this study. Market samples of curd, yoghurt probiotic drink and domestic curd samples were enumerated using formulated and readymade media like M17 for lactococci as well as Streptococcus thermophilus incubated in candle jar at 30ºC and 37ºC respectively for 48 h. The readymade media gave better recovery of viable cells of lactic streptococci. The incorporation of calcium propionate and sodium benzoate at 1.5 and 2 per cent each to M17 agar helped in control of both aerobic spore formers and yeasts. Yeast glucose agar with 0.05 per cent Bromocresol Purple (BCP) showed better viable counts of lactic streptococci. In order to reduce aerobic spore forming bacteria and yeasts, calcium propionate of 0.8 per cent and sodium benzoate of 1.2 per cent incorporation to yeast glucose agar with 0.05 per cent BCP led to formation of more than 8 log counts of purple colonies and staining of colony smear revealed presence of cocci in chains. The purple colonies when inoculated to sterile skim milk set the curd in 8 h with 0.65 per cent lactic acid on an average indicating the presence of lactic streptococci. The findings of the study led to development of selective medium for lactic streptococci with addition of calcium propionate of 0.8 per cent to avoid Bacillus spores and sodium benzoate of 1.2 per cent to inhibit yeast to yeast glucose agar medium which is considered as general purpose medium for lactic streptococci with 0.05 per cent BCP could be used one of the selective medium for the enumeration of lactic streptocci with formation of purple colonies.

Keywords

Lactic streptococci, Yogurt, Candle jar, Aerobic spore formers, Yeast

Conclusion

The readymade medium for lactic streptococci M17 agar medium gave better results when compared to formulated medium. The formulated medium with inhibitory agents like calcium propionate (0.8 %) and sodium benzoate (1.2 %) helped to curb the common contaminants like aerobic bacterial spore formers and yeast, respectively in the fermented milk products. The calcium propionate and sodium benzoate along with pH indicator bromocrseol purple helped in proper expression of viable lactic streptococci inhibiting the common contaminants aerobic spore formers and yeast in fermented milks with differentiating purple colonies.

References

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How to cite this article

Gopal S., Yadav S., Ramachandra B. and Prabha R. (2023). Enumeration of Lactic streptococci from Fermented Milk Products using Differential Medium. Biological Forum – An International Journal, 15(4): 632-636.