Effect of some fermentation conditions on antibacterial activity of fermented milk by kefir grains

摘要

The present study aimed to investigate the effect of type of milk, fermentation time,temperature, and stirring conditions on the antibacterial activity of fermented milk bykefir grains. All fermentation conditions had a significant effect on the antibacterialactivity of kefir samples against four bacteria, except for the effect of temperatureon the diameter of the inhibition zone of Shigella dysenteriae. Considering all factorsand their interactions, fermented samples in full-fat milk compared to nonfat milk,at 37°C compared to 25°C and under stirred conditions compared to non-stirredsamples showed higher antibacterial activity. Also, fermented samples for 48, 72, and120 hr showed higher antibacterial activity against Escherichia coli, Staphylococcusaureus, and Bacillus cereus, respectively, and fermented samples for 48 and 120 hrshowed higher antibacterial activity against S. dysenteriae.Practical applicationsSeveral studies have investigated the antibacterial activity of kefir. But the novelty ofthe present study is that we have also investigated the effect of some fermentationconditions on the antibacterial activity of kefir samples. Furthermore, in this study,the interactions of these variables in the antibacterial activity of kefir samples usingDesign-Expert software have been analyzed. The fermentation conditions had a significanteffect on the antibacterial activity of fermented milk samples. In general, toachieve the most of antibacterial activity, is recommended fermentation in full-fatmilk, at 37°C, and under stirred conditions. In addition to these conditions, to achievethe most antibacterial activity against E. coli, S. aureus, B. cereus, and S. dysenteriae, isrecommended fermentation times of 48, 72, 120, and 120 hr, respectively.