Inhibitory power of kefir: the role of organic acids

Area of Science:

• Microbiology
• Food Science
• Fermentation Technology

Background:

• Kefir, a fermented milk product, is known for its potential health benefits.
• The antimicrobial properties of kefir are attributed to various compounds produced during fermentation.
• Understanding the specific inhibitory mechanisms against pathogenic bacteria is crucial for food safety.

Purpose of the Study:

• To investigate the inhibitory activity of kefir fermented milk and MRS broth against Gram-negative and Gram-positive bacteria.
• To compare the antimicrobial efficacy of kefir with yogurt and artificially acidified milk against Escherichia coli.
• To determine the role of undissociated lactic and acetic acids in kefir's inhibitory action.

Main Methods:

• Kefir grains from different households were used to ferment milk and MRS broth.
• Spot test and agar well diffusion assays were employed to assess inhibitory activity.
• Growth inhibition of Escherichia coli 3 was monitored in nutrient broth under controlled conditions.

Main Results:

• Fermented milk (10 g/100 ml inoculum, pH 3.32-4.25) and MRS broth (1 and 10 g/100 ml inocula, pH 4.18-5.25) exhibited significant inhibitory power.
• Kefir supernatants demonstrated a bacteriostatic effect on Escherichia coli 3 growth.
• Yogurt or artificially acidified milk did not inhibit E. coli 3 growth under the same conditions.

Conclusions:

• Kefir fermentation produces compounds, likely undissociated lactic and acetic acids, that inhibit bacterial growth.
• Kefir exhibits superior antimicrobial activity against Escherichia coli compared to yogurt and artificially acidified milk.
• Kefir fermentation presents a promising natural strategy for controlling pathogenic bacteria in food products.