Effect of some fermentation conditions on antibacterial activity of extracted kefiran from kefir grains

Antibacterial activities of kefir beverage are attributed to kefiran polysaccharide. The aim of this study was to investigate the effect of type of milk, fermentation time, temperature and stirring conditions on antibacterial activity of extracted kefiran from kefir grains. Kefir grains were added to full-fat and non-fat milk. Fermentation was carried out at 25°C and 37°C under stirred and non-stirred conditions. After 24, 48, 72 and 120 hours, the grains were separated from kefir extract and kefiran was extracted. The antibacterial activity of extracted kefiran was carried out by well method. Fermentation time had a significant effect on the inhibition zone of all tested bacteria. Milk type had significant effect on antibacterial activity of kefiran samples against tested bacteria except S. dysenteriae. Fermentation temperature had a significant effect on the inhibition zone of E. coli and B. cereus, but stirring conditions only had significant effect on inhibition zone of B. cereus. Considering all factors and their interactions, in order to extraction of kefiran with higher antibacterial activity is recommended, fermentation in full-fat milk. Also, to achieve higher antibacterial activity against B. cereus, E. coli, S. dysenteriae, and S. aureus, is recommended fermentation time for 24, 48, 48 and 120 hours, respectively. Fermentation at 37°C compared to 25°C and under stirred compared to non-stirred conditions did not create noticeable differences in the antibacterial activity of extracted kefiran from kefir grains. Fermentation conditions had significant effect on antibacterial activity of extracted kefiran from kefir grains.