Chemistry of Natural Compounds, Vol. 47, No. 6, January, 2012 [Russian original No. 6, November–December, 2011]
BIOTRANSFORMATION OF THYMOL BY Aspergillus niger
Akbar Esmaeili*, Abas Khodadadi, and Shila Safaiyan
UDC 547.563.162.1
Biotransformation by cultured plant cells is an important method to convert many organic compounds into more
useful ones, according to the ability of plant cell cultures specifically to produce secondary metabolites[1]. The biotransformation
of menthol by SSCM of Aspergillus niger and Penicillum sp. has been described ꢀ2, 3ꢁ. The reactions involved in the
biotransformation of organic compounds and monoterpene hydrocarbons by culture plant cells include oxidation, reduction,
hydroxylation, esterification, methylation, isomerization, hydrolysis, and glycosylationꢂꢀ4, 5ꢁ.
The biotransformation of thymol, carvacrol, and eugenol by cultured cells of Eucalyptus perriniana has been
studied previously. The cultured cells of E. perriniana are able to convert the aromatic compounds of spices into glycosides,
which are accumulated in the cells ꢀ4ꢁ. Biotranformation of geraniol, nevol, and citral by A. niger produced linalool and
ꢃ-terpineol and some unidentified compounds. With Penicillium regulosum, the major bioconversion product from nerol
and citral was linalool ꢀ6ꢁ.
The biotransformation of menthol by SSCM of A. niger and Penicillium sp. produced menthol from A. niger; the
main products obtained were limonene, p-cymene, and ꢄ-terpinene ꢀ2ꢁ. The main products of biotransformation of thymol
were similar to those obtained in the mentioned work. The bioconversion of (–)-menthol by SSCM of Mucor ramannianus
produced trans-p-menthan-8-ol, trans-menth-2-en-1-ol, sabinane, sabinene, p-menthane-3, 8-diol isomenthol, and 1,8-cineole ꢀ7ꢁ.
The main biotransformation products from menthol by SSCM grown Penicillium sp. were ꢃ-pinene (18.0%),
trans-p-menthan-1-ol (10.6%), p-menth-1-ene (5.8%), sabinene (3.9%), 1.8-cineole (6.4%), and limonene (3.2%) ꢀ3ꢁ.
Using the surface of the organism and adding a methanolic solution converted geraniol to linalool and partially
oxidized it to citral ꢀ8ꢁ.
Fungal isolation was studied and growth conditions of the fungal strain identified in our laboratories in April 2008 in
the province of Tehran, Iran, according to its physiological and morphological characters [9] and according to the physiological
type culture cellection PTCC 5011 of the Iranian Research Organization for Science & Technology, Tehran, Iran.
A spore suspension of A. niger was prepared in nutrient broth solution for inoculation in Petri dishes. The strain was
isolated from a soil sample collected in malt extract agar (MEA) (malt extract agar peptone, 1 g; dextrose, 20 g; agar, 20 g;
distilled water, 1 L) and yeast extract sucrose agar (YES) (Yeast extract, 20 g; sucrose, 150 g; agar, 20 g; distilled water, 1 L)
media. These were used for isolation, cultivation, and identification of the fungal isolate. The same media (without agar) were
used for production and determination of secondary metabolites. A. niger was cultured on yeast extract sucrose or malt extract
media for 10 days at 28 ꢅ 2ꢆC.
The microbial transformation of volatile oil monoterpene by fungal SSCM was examined. Fifteen components
representing 80.1% of the biotransformation of thymol for 10 days were identified, of which toluene (43.4%), 3-methylcyclohexanol
(
9.0%), p-xylene (6.3%), and menthol (4.8%) were found to be the major constituents. Thus the bioconversion of thymol
yields six aromatic hydrocarbons (57.5%), seven oxygenated monoterpenes (12.6%), and two oxygenated hydrocarbons (9.8%).
Two components were identified in the 5-day transformation of thymol, making up 36.7% of the total composition.
3
-Methylcyclohexanol and pentanol were the major components in this bioconversion. Thus, 3-methylcyclohexanol (89.0%)
was identified in the biotransformation (10 days). In this transformation we found one compound. The main component in 5,
0, and 15 days was 3-methylcyclohexanol (2.9%, 9.0%, and 89.0%). As can be seen from the above information, the
1
bioconversion of thymol was an oxidation reaction (Table 1).
Department of Chemical Engineering, North Tehran Branch, Islamic Azad University, P.O. Box 19585/936, Tehran,
Iran, fax: +98 21 88787204, e-mail: akbaresmaeili@yahoo.com. Published in Khimiya Prirodnykh Soedinenii, No. 6,
pp. 843–844, November–December 2011. Original article submitted August 3, 2010.
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0009-3130/12/4706-0966 2012 Springer Science+Business Media, Inc.