Antifungal activity of some essential oil components.

Fifteen essential oil components were evaluated for antifungal activity towards five
spoilage-causing fungi. In liquid shake cultures, unsaturated aldehydes (citral,
cinnamic aldehyde and cittronellal) followed by geraniol, an unsaturated alcohol
were most inhibitory to Aspergillus niger, Fusarium oxysporum and Penicillium
digitatum; their minimal inhibitory concentrations (ME) was 100 clg ml-l. Menthol,
a terpene alcohol was most inhibitory to Rhizopus stolonifer and Mucor sp. with a
iWC of 200 cog ml-l. Hydrocarbons like camphene, limonene and a-terpinene were
least inhibitory. When incorporated in agar medium differentpatterns of activity were
found. Thus citral, cinnamic aldehyde, citronellal, geraniol and menthol not only
failed to completely inhibit A. niger, F. oxysporum and P. digitatum but were more
active against R. stolonifer and Mucor sp. than in liquid medium. The differences
were due to the vapour of the volatile test compounds which accumulated over the agar
medium. The growth inhibition due to the vapours alone was measured by using
structurally modified petri-plates. The vapours were more active against R. stolonifer
and Mucor sp. than against A. niger, F. Oxysporum and P. digitatum. Fungal growth
inhibition by volatile compounds in agar medium reflects the combined activity of th.e
vapour and the compound incorporated in the medium and the inhibition is different
from that obtained in liquid medium. Regarding the structure+xctivity relationship of
citral, the -CHO group in conjugation with a carbon to carbon double bond (C=C) was
found to be responsible for the antifungal activity of the molecule.