The Effect of Some Fermentation Conditions on the Production of Kefiran by Kefir Grains in Fermented Milk

Abstract

Kefir is produced from the fermentation of milk by microorganisms in kefir grains. Kefir grains include lactic acid bacteria, yeast, and acetic acid bacteria surrounded by a protein matrix and polysaccharide called kefiran. One of the most important antibacterial compounds of this beverage is microbial exopolysaccharide of kefiran. The present study aimed to investigate the effect of milk type, fermentation time, temperature, and stirring conditions on the production of kefiran by kefir grains. Activated 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. After 24, 48, 72, and 120 h of fermentation, the grains were separated from kefir extract and kefiran exopolysaccharide was extracted from kefir grains. The effect of these variables and their interaction on the production of kefiran using Design-Expert software and full factorial design have been analyzed. Also, the MIC and MBC of extracted kefiran were determined against Escherichia coli, Staphylococcus aureus, Bacillus cereus, and Shigella dysenteriae. All fermentation conditions and their interactions had a significant effect on kefiran production. Considering the all the fermentation conditions and interaction of all factors, more kefiran were produced in fermented kefir grains at 37°C compared to 25°C, in full-fat milk compared to non-fat milk, under stirred conditions compared to non-stirred and fermented beverages for 48 and 120 hours. MIC and MBC of extracted kefiran for tested bacteria were determined in the range of 1.4-11.25 mg/ml.