Antibacterial activity of kefir drinks prepared under differentfermentation conditions

Background and Aim : Kefir, a complex probiotic, is a microbial symbiotic complex that isobtained from milk fermentation by kefir grains and its consumption is effective in promotinghealth. The biological roles of this fermented beverage and the reproductive capacity of kefir grainsare significantly related to fermentation conditions such as fermentation time, temperature, stirringproportion and type of milk. The aim of the present study was to investigate the effect of differentfermentation conditions on the antibacterial activity of milk fermented by kefir grains.Methods : Activated kefir grains were added to full-fat and non-fat milk and fermentation wasperformed under stirred and non- stirred conditions at ۲۵ and ۳۷°C. After ۲۴, ۴۸, ۷۲ and ۱۲۰ h offermentation, the grains were separated from kefir extract and the antibacterial activity of kefirextract against four gastrointestinal pathogenic bacteria was evaluated based on agar diffusion andusing by well method. The effect of type of milk, fermentation time, temperature and stirringconditions on the antibacterial activity of kefir samples were analyzed.Results : Analysis of variance of mean of inhibition zone diameter of the tested bacteria showedthat, with the exception of the effect of temperature on the mean diameter of the inhibition zone ofS. dysenteriae, all fermentation conditions tested including temperature, stirring conditions, typeof milk and time had a significant effect on the antibacterial activity of kefir samples against fourbacteria.Conclusion : Considering all factors and their interactions, fermented samples at full-fat milk at۳۷°C, under stirred conditions for ۴۸ h for E. coli, for ۴۸ and ۱۲۰ h for S. dysenteriae and B.cereus, and for ۷۲ h for S. aureus showed the highest antibacterial activity.

کلیدواژه ها:

Antibacterial Activity ، Kefir drinks ، Fermentation time ، Fermentation temperature ، Milk type ، Stirring conditions