The synergistic preservative effects of the essential oils of sweet basil (Ocimum basilicum L.) against acid-tolerant food microflora

Essential oils extracted by hydrodistillation from five different varieties of Ocimum basilicum L. plants (Anise, Bush, Cinnamon, Dark Opal and a commercial sample of dried basil) were examined for antimicrobial activity against a wide range of foodborne Gram-positive and -negative bacteria, yeasts and moulds by an agar well diffusion method. All five essential oils of basil showed antimicrobial activity against most of the organisms tested with the exception of Flavimonas oryzihabitans and Pseudomonas species. The inhibitory effect of Anise oil, in comparison with mixtures of the predominant components of pure linalool and methyl chavicol, against the acid-tolerant organisms, Lactobacillus curvatus and Saccharomyces cerevisiae , was examined in broth by an indirect impedance method. Synergistic effects between Anise oil, low pH (pH 4·2) and salt (5% NaCl) were determined. The antimicrobial effect of Anise oil was also assessed in a tomato juice medium by direct viable count, showing that the growth of Lact. curvatus and S. cerevisiae was completely inhibited by 0·1% and 1% Anise oil, respectively. The results of the current study indicate the need for further investigations to understand the antimicrobial effects of basil oils in the presence of other food ingredients and preservation parameters.