Physicochemical characterization and antibacterial activity of Brazilian artisanal milk kefir

Milk kefir has an acidic taste and creamy consistency and results from the fermentation of milk by the microorganisms present in kefir grains. Milk kefir is known worldwide for its health benefits attributed to various bioactive compounds, including organic acids, bioactive peptides, and bacteriocins. This study evaluated the physicochemical composition of Brazilian artisanal milk kefir samples and studied the antibacterial activity of kefir beverage and of microorganisms isolated from kefir against potentially pathogenic bacteria. During the 24 and 48 h kefir fermentation, reducing sugars and pH decreased and lactic acid concentration increased. Kefir fermented in 48 h completely inhibited the bacterial growth of Staphylococcus aureus, Salmonella enterica and Escherichia coli. Of the 29 microorganisms isolated from kefir, 10 strains (34.5%) showed inhibitory activity against S. aureus, Bacillus cereus, Streptococcus mutans, Klebsiella pneumoniae, S. enterica and E. coli. These strains showed inhibition zones of 12-40 mm against potentially pathogenic bacteria tested. Based on the antagonist capacity of the microorganisms isolated from milk kefir, these strains have potential to be used as food preservatives and as probiotic agents.