Seventeen microbial species including 10 fungal taxa, two yeasts and five bacteria, were isolated from freshly prepared orange, guava and banana juices kept in open bottles at room temperature for 7 days. Eight different essential oils, from local herbs, were tested for their antimicrobial activity against these test organisms. The essential oils of Cymbopogon citratus , Ocimum basilicum and Origanum majorana were found to be highly effective against these microorganisms. Aspergillus niger , A. flavus and Saccharomyces cerevisiae , the most prevalent microorganisms in juice, showed the highest resistance against these essential oils. GC-MS analysis showed that while e-citral, a'-myrcene, and z-citral represent the major components (75.1%) of the essential oil of Cymbopogon citratus ; bezynen,1-methyl-4-(2-propenyl), 1,8-cineole and trans-a'-bisabolene were the main components (90.6%) of Ocimum basilicum ; whereas 3-cyclohexen-1-01,4-methyl-1(1-methylethyl)-(CAS), c-terpinene and trans-caryophyllene represent the major components (65.1%) of Origanum majorana . These three essential oils were introduced into juices by two techniques namely, fumigation and direct contact. The former technique showed more fungicidal effect than the latter one against A. flavus , A. niger , and S. cerevisiae . The essential oil of Cymbopogon citratus by comparison to other test oils showed the strongest effect against these fungi with a minimum inhibitory concentration of 1.5 μl/ ml medium and a sublethal concentration of 1.0 μl/ ml . The antimicrobial activity of this oil is thermostable at 121℃ for 30 min.
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