Attempts were made to isolate natural antagonistic lactic acid bacteria (LAB) and use them in production of dahi and raita for increased safety. Seventy isolates of LAB were isolated from dahi obtained from different sources. These isolates were tested for their antagonistic activity against selected pathogenic strains of Staphylococcus aureus subsp. aureus and Escherichia coli AB 1157 by adopting agar well assay method. Out of the 70 lactic acid bacterial isolates, 8 were found to have antagonistic activity against both pathogenic organisms. These isolates achieved the desired fermentation rate. Dahi produced by these isolates was found acceptable according to sensory evaluation. The LAB isolates with antagonistic activity were identified by molecular characterization. It is concluded that the identified antagonistic cultures were effective in inhibiting the growth of E. coli and Sta. aureus in dahi and raita.

Practical Applications

Milk products like dahi and raita are widely consumed, and market for them has existed in many parts of the world for many generations. There is an increased demand by the consumer for high-quality natural food, free from artificial preservatives and contaminating microorganisms. The presence of Escherichia coli in milk products indicates the presence of enteropathogenic microorganisms, which constitute a public health hazard. Staphylococcus aureus causes minor skin infection to life-threatening diseases such as pneumonia, meningitis, endocarditis and septicemia. Because the fermented products are very popular in Indian diet, the use of a starter culture that can ferment as well as check the growth of pathogenic organism would be very ideal. Hence, novel antagonistic strains of lactic acid bacteria was identified from natural sources and used successfully as starter culture for production of indigenous fermented milk products, namely dahi and raita, with increased safety.