Abstract
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.