Antimicrobial effect of rosemary extracts

Area of Science:

• Food Science
• Microbiology
• Natural Product Chemistry

Background:

• Rosemary extract (Oxy'less) is commercially used as a lipid antioxidant in food.
• Understanding its antimicrobial properties is crucial for food safety applications.

Purpose of the Study:

• To evaluate the antimicrobial activity of an ethanolic rosemary extract against various foodborne microorganisms.
• To investigate the influence of media composition on the extract's efficacy.

Main Methods:

• Minimum Inhibitory Concentration (MIC) assays were performed on gram-positive bacteria, gram-negative bacteria, yeasts, and fungi.
• The effect of pH, NaCl concentration, temperature, and food matrix components on antimicrobial activity was assessed.
• Heat stability of the extract was also evaluated.

Main Results:

• The rosemary extract demonstrated significant activity against gram-positive bacteria (e.g., Bacillus cereus, Streptococcus mutans) and inhibited fungal growth.
• No activity was observed against tested gram-negative bacteria and yeasts at concentrations up to 1%.
• Antimicrobial activity was enhanced by low pH, high NaCl content, and low temperatures, with synergistic effects noted for Staphylococcus aureus.

Conclusions:

• Rosemary extract possesses notable antibacterial properties against specific foodborne pathogens, especially gram-positive bacteria.
• Media composition, including pH and salt, significantly modulates its antimicrobial efficacy.
• The extract's activity is linked to hexane-extractable compounds, likely phenolic diterpenoids.