Magnolia grandis is a large evergreen tree species that grows in China and Vietnam. The species is used for timber and is evaluated as critically endangered species. In an APRC publication, the leaves, twigs and ripe fruits of M. grandis, growing wild in Ha Giang Province of Vietnam, were hydrodistilled to obtain the essential oils.
The common feature of these oil samples was that they contain α-pinene as a main component of the oils. In addition, all of three analyzed oil samples were richer in monoterpene compounds than in sesquiterpene compounds. The main compounds in the oils of M. grandis species in the present study were different to those of other Magnolias, for example, (Z)-β-ocimene, (E)-β-ocimene, and germacrene A were the main compounds of M. acuminata leaf oil; β-pinene of M. calophylla and M. virginiana leaf oils; (Z)-β-ocimene, germacrene A and β-bisabolene of M. grandiflora leaf oil; β-pinene, 1,8-cineole, β-elemene were the main compounds of M. grandiflora leaf, flower, immature fruit and mature fruit oils; α-terpinene, bicyclogermacrene, and aristolene were the main compounds of M. figo leaf oil, naphthalene, and α-bulnesene were the main compounds of M. ovata (syn. Talauma ovata) fruit oil. The variation of essential oil of one plant species or of different plant species may due to various factors such as seasons in the year, development stage of plants, geographic regions, as well as genetic differences.
Essential oils of M. grandis were then determined the minimum inhibitory concentration (MIC) and median inhibitory concentration (IC50) values through microbroth dilution assays using 7 strains of microorganisms: Staphylococcus aureus, Bacillus subtilis, and Lactobacillus fermentum, Salmonella enterica, Escherichia coli, Pseudomonas aeruginosa, and Candida albicans. The results of the assay evaluated after 16-24 hours of incubation are presented in the table below.
Although the antimicrobial activities of M. grandis essential oils were marginal at best, the leaf essential oil from M. grandis expressed stronger inhibitory effects on the seven test microorganisms than the twig and ripe fruit oils. IC50 values of the M. grandis leaf, twig and ripe fruit oils were from 683 to 7851 μg/mL, from 1499 to 10,012 μg/mL and from 939 to 6599 μg/mL. MIC values of these oils ranged from 2048 to > 16,384 μg/mL, from 8192 to > 16,384 μg/mL and from 4096 to > 16,384 μg/mL, respectively. S. aureus, E. coli, and C. albicans were more sensitive to the essential oils than four other tested microorganisms. The higher activity of the M. grandis leaf oil could be associated with higher amounts of oxygenated monoterpenes and oxygenated sesquiterpenes than the ones in the twig and ripe fruit oils. Previous study demonstrated that essential oils rich in oxygenated compounds are more active as antimicrobial agents than essential oils with large amounts of hydrocarbons.
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