5484 J. Agric. Food Chem., Vol. 50, No. 19, 2002
Yanagimoto et al.
(6) Shibamoto, T. Heterocyclic compounds in browning and brown-
ing/nitrite model systems: Occurrence, formation mechanisms,
flavor characteristics and mutagenic activity. In Instrumental
Analysis of Foods; Charalambous, G., Inglett, G., Eds.; Academic
Press: New York, 1983; Vol. I, pp 229-278.
(7) Eiserich, J. P.; Wong, J. W.; Shibamoto, T. Antioxidative
activities of furan and thiophenethiols measured in lipid peroxi-
dation systems and by tyrosyl radical scavenging assay. J. Agric.
Food Chem. 1995, 43, 647-650.
(8) Shaker, E. S.; Ghazy, M. A.; Shibamoto, T. Antioxidative activity
of volatile browning reaction products and related compounds
in a hexanal/hexanoic acid system. J. Agric. Food Chem. 1995,
43, 1017-1022.
(9) Eiserich, J. P.; Shibamoto, T. Antioxidative activity of volatile
heterocyclic compounds. J. Agric. Food Chem. 1994, 42, 1060-
1063.
(10) Fuster, M. D.; Mitchell, A. E.; Ochi, H.; Shibamoto, T.
Antioxidative activities of heterocyclic compounds formed in
brewed coffee. J. Agric. Food Chem. 2000, 48, 5600-5603.
(11) Lee, K. G.; Shibamoto, T. Antioxidant property of aroma extract
isolated from clove buds [Syzygium aromaticum (L.) Merr. et
Perry]. Food Chem. 2001, 74, 443-448.
(12) Lee, K. G.; Shibamoto, T. Antioxidant activities of volatile
components isolated from Eucalyptus species. J. Sci. Food Agric.
2001, 81, 1573-1579.
1-methyl-1,3-dihydropyrrole-2-one. The second keto-enol tau-
tomerization steps occur, and 1-methyl-2,5-pyrrolidinedione is
finally produced. Similar to 1-methyl-2,5-pyrrolidinedione
formation, production of 2,5-pyrrolidinedione has been previ-
ously reported in pyrrole oxidation (20). However, in that study
a mechanism for 1H-pyrrole-2,5-dione formation from pyrrole
was not proposed. As shown in Table 1, furans produced their
oxidized products except furan and 2-acetylfuran. No oxidized
products from furan and 2-acetylfuran were detected by GC-
MS. 2-Methylthiophene and 2-thiophenecarboxaldehyde pro-
duced 5-methyl-2(5H)-thiophenone and 2(5H)-thiophenone as
their respective oxidized products. In the case of 2-ethylth-
iophene, the ethyl group on the thiophene ring was oxidized to
an acetyl group. This result demonstrates that the hydroxyl
radical directly attacked the ethyl group on the thiophene. Most
of the thiazoles and pyrazines, except for 2-methylpyrazine, did
not produce oxidized products. This result may indicate that
thiazoles and pyrazines are unable to scavenge hydroxyl radicals.
The results from the present study indicate that some of the
heterocyclic compounds present in coffee possess antioxidative
activity, although this activity is not as strong as that of the
synthetic antioxidant butylated hydroxytoluene (BHT). However,
because tremendous numbers of these heterocyclic compounds
are present in coffee, their combined activity might be compa-
rable to those of known antioxidants.
(13) Ettre, L. S. Interpretation of analytical results. In The Practice
of Gas Chromatography; Ettre, L. S., Zlatkis, A., Eds.; Inter-
science Publishers: New York, 1967; p 402.
The levels of chemicals tested in the present study are
considerably higher than levels present in actual brewed coffee.
Levels of heterocyclic flavor compounds found in brewed coffee
range from micrograms to milligrams per kilogram. However,
it is important to know the antioxidative activities of chemicals
first in order to investigate the possible presence of antioxidants
in brewed coffee. Once activity is demonstrated, the next step
is to investigate their activity at the more relevant low levels
shown above. Therefore, investigation of the antioxidative
activity of the chemicals at the levels of micrograms to
milligrams per kilogram is in order.
(14) Mahanti, M. K. Simple molecular orbital calculations in the
structural elucidation of organic molecules. Perturbations of
heterocyclic systems. Indian J. Chem. 1977, 15B, 168-174.
(15) Samuni, A.; Neta, P. Electron spin resonance study of the reaction
of hydroxyl radicals with pyrrole, imidazole, and related
compounds. J. Phys. Chem. 1973, 77, 1629-1635.
(16) Horner, L. Autoxidation of various organic substances. In
Autoxidation and Antioxidants; Lundberg, W. O., Ed.; Wiley:
New York, 1961; pp 197-202.
(17) Nonhebel, D. C.; Tedder, J. M.; Walton, J. C. Radicals;
Cambridge University Press: London, U.K., 1979; p 157.
(18) Singhara, A.; Macku, C.; Shibamoto, T. Antioxidative activity
of brewed coffee extracts. In Functional Foods for Disease
PreVention II: Medicinal Plants and Other Foods; ACS
Symposium Series 701; Shibamoto, T., Terao, J., Osawa, T.,
Eds.; American Chemical Society: Washington, DC, 1998; pp
101-109.
(19) Van Deurzen, M. P. J.; Van Rantwijk, F.; Sheldon, R. A.
Synthesis of substituted oxindoles by chloroperoxidase catalyzed
oxidation of indoles. J. Mol. Catal. B 1996, 2, 33-42.
(20) Ribo, J. M.; Serra, X. Reactivity of pyrrole pigments. Part VII
autoxidation of model compounds for 5(2H)-dipyrrylmethanones
and 3,4-dihydro-5(1H)-pyrromethenones. Monatsh. Chem. 1986,
117, 185-200.
LITERATURE CITED
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Received for review April 23, 2002. Revised manuscript received July
6, 2002. Accepted July 6, 2002.
(5) Macku, C.; Shibamoto, T. Volatile antioxidants produced from
heated corn oil/glycine model system. J. Agric. Food Chem.
1991, 39, 1990-1993.
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