In vitro antimicrobial and antioxidant activity of commercial rosemary extract formulations

Phenolic plant extracts are sources of natural bioactive compounds, which can inhibit the rate of food spoilage. MIC and MBC concentrations of four oil- or water-soluble rosemary (Rosmarinus officinalis) extracts against gram-positive (Bacillus and Staphylococcus) and gram-negative (Campylobacter and Salmonella) bacteria were determined by using disk diffusion, agar dilution, and broth microdilution methods, as well as bacterial survival kinetics in a macrodilution test. To describe the antioxidant properties of the extracts, the reducing power, free radical scavenging effectiveness, and beta-carotene bleaching test were used. The antimicrobial and antioxidant activity depended on the concentration and chemical nature of the phenolic compounds in the extracts. Gram-positive bacteria were more sensitive than were gram-negative bacteria, especially for oil-soluble extracts with carnosic acid as the major phenolic compound. A microdilution method based on ATP measurement was found to be a useful, rapid technique for determining antibacterial efficiency, and its results correlated well with MICs from survival curve measurement. Reducing power and free radical scavenging effectiveness was higher in water-soluble formulations, according to their higher total phenolic content, but in an aqueous emulsion system of linoleic acid, they exhibited lower antioxidant activity. This correlated well with the higher efficiency of antimicrobial activity of oil-soluble formulations, despite the lower total phenolic content of these extracts.