Antimicrobial effect of rosemary extracts

A rosemary extract commercially exploited (Oxy'less) as an antioxidant of l ipids in foods was dissolved in ethanol (100 mg/ml), and the solution was t ested against foodborne microorganisms. For gram-positive bacteria, the MIC of the ethanolic solution was 1% for Leuconostoc mesenteroides, 0.5% for L isteria monocytogenes, 0.5% for Staphylococcus aureus, 0.13% for Streptococ cus mutans, and 0.06% for Bacillus cereus. It slowed the growth of Penicill ium roquefortii and Botrytis cinerea. Up to 1% of the ethanolic solution ha d no activity on the gram-negative bacteria Escherichia coli, Salmonella En teritidis, and Erwinia carotovora and on the yeasts Rhodotorula glutinis an d Cryptococcus laurentii. Antibacterial activity of the rosemary extract wa s strongly influenced by the composition of the media. The MIC was reduced by low pH, high NaCl contents, and low temperatures. Low pH and high NaCl c oncentration had a synergistic effect on the MIC of the rosemary extract fo r S. aureus. Lipids, surface-active agents, and some proteins decreased its antibacterial activity, whereas pectin had no effect. The inhibitory effec t was little modified by heat treatment (100 degrees C). The natural microf lora of pasteurized zucchini broth was inhibited by 0.5% of the rosemary ex tract. The antibacterial activity was linked to the compounds extracted wit h hexane, which are presumably phenolic diterpenoids.