Vol.4, No.8, 433-442 (2013) Agricultural Sciences
http://dx.doi.org/10.4236/as.2013.48058
Quality aspects of coffees and teas: Application of
electron paramagnetic resonance (EPR)
spectroscopy to the elucidation of free radical and
other processes
Bernard A. Goodman1*, Chahan Yeretzian2, Klaus Stolze3, Deng Wen4
1State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, Guangxi University, Nanning, China;
*Corresponding Author:
2Zurich University of Applied Sciences, Institute of Chemistry and Biological Chemistry, Wädenswil, Switzerland
3Institute of Pharmacology and Toxicology, Dept. Biomedical Sciences, University of Veterinary Medicine, Vienna, Austria
4Department of Physics, Guangxi University, Nanning, China
Received 17 April 2013; revised 18 May 2013; accepted 15 June 2013
Copyright © 2013 Bernard A. Goodman et al. This is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
Coffees and teas are beverages that are both
exceptionally rich in antioxidant molecules, and
are also both associated with beneficial health
effects. Thus although the quality characteris-
tics of these beverages are conventionally as-
sessed on the basis of their sensory properties,
their antioxidant contents represent an addi-
tional and increasingly valued attribute of qual-
ity based on their contributions to healthy diets.
Both beverages are prepared by hot water ex-
traction of a pure plant-derived product, and
thus their compositions can potentially change
quite rapidly as a result of oxidation in contact
with air. Oxidative processes often proceed via
free radical intermediates, and sometimes also
result in the formation of stable radical end-
products; thus EPR spectroscopy is a conven-
ient technique for investigating some of the
various free radical reactions that occur in these
beverages. This paper reviews progress that has
been made in elucidating free radical processes
that occur during the preparation and storage of
coffees and teas, and the results are discussed
in terms of quality criteria of the beverages.
Keywords: Coffee; Tea; Free Radicals;
Antioxidants; EPR Spectroscopy; Quality
1. INTRODUCTION
Coffees and teas are two of the most heavily con-
sumed beverages in the World. Both have a history of
links to medicinal properties, although neither is conven-
tionally considered to be a traditional medicine. Conven-
tionally the qualities of teas and coffees are assessed on
the basis of their sensory properties by expert panels of
tasters, as these are relevant to the primary and direct/im-
mediate experiences of consumers. Yet, we have learned
over recent years that both beverages contain molecules
that are considered to be beneficial to long-term health
and well-being, a quality that is increasingly noticed and
valued by consumers. Hence our definition and under-
standing of quality in coffee and tea are slowly but sus-
tainably being extended to one that contains long term
health benefits in addition to the immediate sensory im-
pact.
The major beneficial molecules belong to a class of
compound known as antioxidants, whose principal func-
tion in biology is to protect cells from oxidative damage.
They do this in one of three ways; 1) by inhibiting the
formation of oxidizing agents, 2) by selectively scav-
enging oxidizing agents, or 3) by scavenging the prod-
ucts of the reactions of oxidizing agents, which may
themselves be capable of causing cellular damage. Me-
chanism 1) generally involves antioxidant enzymes,
whereas 2) and 3) may be performed by either small or
large molecules. However, a common property of biolo-
gical antioxidants is their ability to redox cycle between
reduced and oxidized forms, both of which are generally
stable.
The stable form of molecular oxygen, 3O2, is a free
radical with two unpaired electrons, and various products
derived from it are known as reactive oxygen species
(ROS), because they tend to be more reactive than O2
itself. Some of these are also free radicals, including the

B. A. Goodman et al. / Agricultural Sciences 4 (2013) 433-442
434
products of its 1-electron reduction, 2 and its proto-
nated form .OOH, as well as the hydroxyl radical .OH,
whereas others, such as its unstable form, 1O2, and hy-
drogen peroxide, H2O2, are diamagnetic. However, both
1O2 and H2O2 readily participate in reactions that lead to
free radical generation, and free radicals are a common
feature of biological oxidation processes. Thus antioxi-
dants are often assumed to be free radical scavengers,
and although this is an oversimplification of their chemi-
cal behavior, there are close links between antioxidants
and the control of free radical reactions in biological and
complex food systems.
O
Since coffee and tea are the major sources of antioxi-
dants in many diets (e.g. [1,2]) and may also be stored
for long periods in air, it might be expected that oxida-
tion processes could influence their antioxidant contents,
or at the very least result in changes in their forms which
could impact on the chemical composition of the bever-
ages subsequently prepared by hot water extraction.
However, such reactions are extremely complex, and it is
only now that we are starting to develop an understand-
ing of the various chemical processes that are involved.
The current paper addresses various aspects of the bev-
erage production in which O2-derived free radicals are
involved, and illustrates these with results obtained using
electron paramagnetic resonance (EPR) spectroscopy, a
technique which is based on measurements of chemical
species with unpaired electrons, such as free radicals and
paramagnetic metal ions and complexes.
2. ANTIOXIDANTS AND FREE RADICAL
SPECIES IN COFFEE PRODUCTION
Although coffee is most commonly associated with the
alkaloid caffeine, which has been considered to have
some antioxidant properties as a result of its conversion
to oxocaffeine (1-methyl uric acid) during coffee oxida-
tion [3], there are other bioactive compounds in the bev-
erage. Furthermore, caffeine is not a true antioxidant
because oxocaffeine formation in the beverage is proba-
bly the result of reaction with hydroxyl radicals, which
react virtually indiscriminately with organic molecules.
Green coffee beans are a rich source of chlorogenic
acids, a family of polyphenol antioxidants that feature in
a number of traditional Asian medicines (e.g. [4,5]), and
to which beneficial health effects from the consumption
of coffee have been attributed [6]. The chlorogenic acids
(Figure 1) are esters of quinic acid and various poly-
phenols, but mainly caffeic, p-coumaric and ferulic acids
[7,8]. Various mono-, di- and tri-esters exist and 70 dif-
ferent chlorogenic acids have been identified in extracts
of green coffee beans [9].
The major changes to coffee beans that occur during
roasting are the formation of melanoidins, ill-defined
colored materials, via the Maillard and caramelization
reactions. The Maillard reaction involves a condensation
reaction between free amino groups of amino acids, pep-
tides or proteins with carbonyl groups of reducing sugars,
whereas the caramelization reaction is based on reactions
involving sugars or carbohydrates alone. However, both
reactions are extremely complex and result in the genera-
tion of a wide range of products, including the mela-
noidins. Although melanoidins have been described as
possessing mutagenic activity [10,11], they are also as-
sociated with beneficial health properties (e.g. [12]).
Furthermore, the Maillard reaction produces compounds
with strong antioxidant properties [13], and coffee is
overall described as being anticarcinogenic [14,15].
Understanding the chemistry of the coffee roasting
process is a major challenge, but one that is necessary in
order to refine existing procedures to produce higher
quality products. During roasting, the contents of chloro-
genic acids decrease, although some are incorporated
into the melanoidin components from which they may
subsequently be released during digestion [16]. However,
Figure 1. Chemical structures of chlorogenic acids; these are esters of quinic acid and
1 or more phenolic acids, such as p-coumaric, caffeic or ferulic acid/.

B. A. Goodman et al. / Agricultural Sciences 4 (2013) 433-442 435
because of the antioxidant properties of melanoidins, the
roasting process results in an overall increase in the an-
tioxidant content of the beverage, with maximum activity
being reported for medium roasted beans [17,18]. The
roasting of coffee also results in the formation of sub-
stantial quantities of free radicals (e.g. [19]), the contents
of which are influenced by a number of factors including
the water content of the green beans prior to roasting
[20].
It is in addressing issues involving free radicals and
other paramagnetic chemical species that EPR spectros-
copy can make important contributions to the science of
coffee. Changes in free radical concentrations can be
monitored in essentially real time in an EPR spectrome-
ter (Figure 2) [21], and thus this technique allows the
possibility of investigating how variables such as the
temperature profile and gas flow rate influence free radi-
cal concentrations during the roasting process for differ-
ent bean types.
The formation of both antioxidant molecules and free
radicals during the coffee roasting process demonstrates
that the two processes are not inversely related, as might
be expected if the principal role for antioxidants was to
inhibit the production of, or to selectively scavenge, free
radicals. Indeed, with commercial “instant” coffees,
Pascual et al. [22] showed that there was no correlation
between their antioxidant and free radical contents.
3. OXIDATIVE PROCESSES DURING
THE STORAGE OF ROASTED
COFFEE PRODUCTS
Oxidative processes influence the composition of
roasted coffees during subsequent storage, as evidenced
by increases in their levels of lipid peroxidation [23-25].
Furthermore, storage in air results in a progressive in-
crease in the EPR free radical signal [26], whereas in the
absence of air a progressive decrease is observed [27].
These results thus illustrate that the roasted coffee is not
an inert material, and that changes in the free radical
components are the result of processes that involve both
formation and decay. In addition, the recent work of
Yeretzian et al. [26] has demonstrated that the increase in
free radical signal during storage in air of roasted and
ground (R&G) coffee is mainly the result of reaction of
coffee components with O2 and not directly the result of
physical damage caused by the grinding process.
Figure 2. Profiles for EPR free radical signal intensities during the roasting in N2 of (a)
Robusta and (b) Arabica coffee beans (adapted from reference [21]). Note the much
higher free radical concentration in Arabica beans.

B. A. Goodman et al. / Agricultural Sciences 4 (2013) 433-442
436
4. FREE RADICAL REACTIONS IN
COFFEE BEVERAGES
After preparation, the sensory characteristics of coffee
beverages change rapidly. EPR measurements show that
changes in free radical contents also occur, and although
“cause and effect” relationships have not been estab-
lished it seems likely that hydroxyl radicals are involved,
because of the presence in coffee of the chemical com-
ponents appropriate for Fenton reaction chemistry [28].
With solutions of “instant” coffee, Pascual et al. [29]
described a temperature independent decay of the initial
free radical signal on a timescale similar to that observed
by Hofmann et al. [30] for the radicals formed on disso-
lution in water of 1,4-dialkylpyrazinium diquaternary
salts (diquat), which are early products of the Maillard
reaction. However, Pascual et al. [29] also observed a
temperature dependent production of a free radical signal
with similar spectral characteristics to that of the original
radical, a result which indicates that free radical reactions
occur continuously in the coffee beverage. Furthermore,
these authors also demonstrated that O2 was involved in
the production of this new signal, possibly as a source of
hydroxyl radicals by enzymatic conversion to H2O2 [31]
followed by Fenton reaction chemistry. Although chemi-
cal spin trapping combined with EPR spectroscopy is a
recognized method for the identification of unstable free
radical intermediates (e.g. [32]), the results of such
measurements indicated the trapping of C-centred radi-
cals. However, unlike the superoxide radical anion (2
O

),
the hydroxyl radical reacts virtually indiscriminately
with organic molecules. Thus in complex systems such
as coffee solutions, most of these radicals will react via
hydrogen atom extraction with organic components in
the beverage and it is the resulting C-centred radicals that
are observed after reaction with the spin trap.
5. PROBLEMS ASSOCIATED WITH THE
STORAGE OF LIQUID COFFEE
PRODUCTS
As mentioned in the previous paragraph, the sensory
properties change rapidly after preparation of coffee
beverages. In addition to shedding light on the short term
radical processes that occur in the beverage, EPR spec-
troscopy has also been shown to be potentially useful in
understanding processes that occur during longer term
storage of liquid coffee products under controlled condi-
tions. Recently, Pascual et al. [33] have used EPR spec-
troscopy to investigate the effects of various factors that
affect the stability of liquid coffee prepared from aque-
ous extracts of whole roasted coffee beans. They found
that the free radical EPR signal intensity is sensitive to
the O2 content of the water used for extraction and the
storage temperature, but not the storage atmosphere
(headspace). In similar measurements on concentrated
coffee solutions, Yeretzian et al. [34] (2013) also ob-
served that the O2 content of the water used for extrac-
tion was the largest factor which affected the changes in
the free radical EPR signal during storage. However,
whereas the intensities of the signal from whole bean
extracts increased during storage, those from coffee con-
centrates decreased, thus indicating the difficulties in
producing simple interpretations of the results from such
measurements.
6. DEGRADATION OF COFFEE AROMA
The aroma of coffee that is generated during the roast-
ing process is considered to be one of the most attractive
features of the beverage, and it is generally considered to
represent an important quality criterion. However, its
chemical composition is extremely complex, and repre-
sents the combination of many hundreds (thousands?) of
molecules, each of which is present in small concentra-
tion [35]. Furthermore, several key aroma molecules,
especially those containing thiol groups, have limited
stability with respect to oxidation, and as a result the sen-
sory properties decline during storage. One such mole-
cule is furfuryl mercaptan, and its decomposition under
Fenton reaction conditions has been investigated in detail
by Blank et al. [36]. This reaction was found to be ex-
tremely complex and involved the generation of both C-
and S-centred radical species in early stages of the deg-
radation process.
An ab initio computational approach to explore the
stability of a wide range of coffee aroma compounds has
been reported by Munro et al. [37]. These studies fo-
cused on the various free radical processes that might
lead to aroma degradation during storage of liquid coffee,
and involved investigation of >100 radicals that might be
formed during the reactions of key aroma compounds.
These radical products were classified according to their
thermodynamic stabilities relative to common radical
sources that might exist in liquid coffee extracts. The re-
sults predicted that most aroma molecules should be re-
sistant to both peroxidation and attack from phenolic
antioxidants, but are unstable with respect to reaction
with •OH.
7. ANTIOXIDANTS IN TEA LEAVES AND
THEIR CHANGES DURING
PROCESSING
The tea beverage is prepared by hot water extraction
of dried leaves of the plant Camellia sinensis. Different
types of tea are classified according to the degree of
processing to which the leaves are subjected prior to
packaging, with the amount of oxidation increasing in
the order white  green < red < black (Note the Chinese
red tea is roughly equivalent to the Indian black tea,

B. A. Goodman et al. / Agricultural Sciences 4 (2013) 433-442 437
whereas the Chinese Pu’er tea is a black tea that is al-
lowed to undergo some fermentation before being proc-
essed). The stability (shelf life) of the products follows a
similar trend and Pu’er tea is stable over many decades.
All teas contain substantial quantities of polyphenolic
antioxidants, but their molecular compositions and sizes
increase according to the degree of oxidation they ex-
perience during processing. Thus the polyphenols in the
lightly processed white and green teas are dominated by
relatively simple catechins, known as green tea poly-
phenols (GTP); the major GTP are (−)-epigallocatechin
gallate (EGCG), (−)-epigallocatechin (EGC), (−)-epicate-
chin gallate (ECG), (−)-epicatechin (EC), and (+)-catechin
(CT) (Figure 3). In addition, gallic acid (GA) may also
be observed. In contrast, the dominant polyphenols in
black teas the more complex theaflavins, thearubigins
and more highly polymerized substances [38]. The GTP
have received considerable attention for the association
of green tea consumption with beneficial health proper-
ties (e.g. [39-42]), but there is evidence that the various
types of tea have similar beneficial health effects [43,44].
8. AUTOXIDATION REACTIONS IN TEAS
As mentioned in the previous section, teas contain ap-
preciable quantities of polyphenols, which are generally
assumed to be responsible for the beneficial health ef-
fects of the beverage. During their behavior as antioxi-
dants, polyphenols are oxidized to phenoxy or more
commonly semiquinone radicals, and this reaction pro-
ceeds more rapidly at high pH values. Consequently,
alkaline autoxidation is often used as an experimental
procedure for accelerated oxidation in order to under-
stand the chemistry of the tea polyphenols. Under such
conditions, EPR spectra can be readily observed (Figure
4), and results show that signals are observed from each
of the main green tea polyphenols in alkaline solutions of
green tea extracts (e.g. [45-47]), whereas the spectra
from equivalent black tea samples are dominated by the
radical corresponding to oxidized gallic acid [45,46].
Thus there may be considerable differences in the anti-
oxidant chemistry reactions of different types of tea, and
EPR could be a useful technique for comparing reactions
in teas that have been subjected to different types of
processing. However, caution needs to be exercised in
extrapolating results from alkaline autoxidation to reac-
tions under physiological conditions, since oxidation of
EGCG by superoxide at near neutral pH values proceeds
via a different mechanism to that observed on alkaline
autoxidation [47].
An important property of plant-derived polyphenols is
their ability to function as antimicrobial molecules [48-
52]. However, the microbial degradation of white/green
tea leaves has a major effect not just on the easily oxidi-
zable GTP, but also other compounds such as caffeine,
which generally are not susceptible to alteration during
storage (Klaus Stolze, unpublished results). This then
represents another example of complex chemical behave-
ior in a beverage that needs to be investigated further.
9. OTHER MOLECULES IN TEA
EXTRACTS THAT COULD
CONTRIBUTE TO THEIR BIOACTIVITY
The potentially beneficial molecules in teas are not
limited to their polyphenolic components, and other bio-
Figure 3. Chemical structures of the green tea polyphenols (−)-epicatechin (EC), (+)-
catechin (CT), (−)-epigallocatechin (EGC), (−)-epicatechin gallate (ECG), and (−)-
epigallocatechin gallate (EGCG).

B. A. Goodman et al. / Agricultural Sciences 4 (2013) 433-442
438
Figure 4. EPR spectra of autoxidized (a) green tea and (b) black (Pu’er) tea. Details
of the interpretation of the green tea spectrum are given in reference [47].
active molecules are present in the beverage. As with
coffee, caffeine is a significant component, albeit at ap-
preciably lower concentrations than in coffee [38]. The
principal amino acid in tea is theanine (5-N-ethyl-
glutamine) [53,54], which has been shown to be effective
in reducing mental and physical stress [55] and to
improving cognition in impaired subjects [56]. It has also
been proposed to be able to provide protection against
dementia [57], and is thus complementary to caffeine in
its effects on neurodegeneration. Furthermore, although
the neurological effects associated with tea consumption
have been attributed to the metal chelating properties of
EGCG (by inhibiting the formation of β-amyloid plaques)
[58], there is little soluble chelate formation on reaction
of Cu(II) with the GTP EGCG and GA at neutral and
acidic pH values [59,60]. In contrast, the teas themselves
are able to form soluble Cu(II) complexes over a wide
range of pH values [46,61]. Thus it seems likely that
molecules in tea other than the GTP are responsible for
metal chelation under physiological conditions. Theanine
does form Cu(II) complexes under acidic conditions but
Goodman et al. [61] have reported the presence of an
additional (as yet unidentified) compound in teas that can
form complexes with Cu(II) at pH < 2.
10. GENERAL DISCUSSION,
CONCLUSIONS AND FORWARD
LOOK
We are only now starting to get an appreciation of the
roles played by antioxidants and free radical reactions in
the chemistry of coffees and teas, but their relationships
to conventional quality assessment based on sensory
properties are still largely uninvestigated. However, it is
now recognized that foods rich in antioxidants are asso-
ciated with beneficial health properties, and consequently
both coffees and teas can make valuable contributions to
healthy diets.
In coffees, the main antioxidants are the chlorogenic
acids and melanoidins, with the relative importance of
these two groups of molecule being dependent on both
the plant genetics and the darkness of the roast. The me-
dicinal properties of chlorogenic acids are well known
(e.g. [4,5]), and these molecules feature in a number of
traditional Asia medicines, but there is still controversy
concerning the biological effects of the melanoidins.
Thus these molecules need further investigation and
characterization, but this is a highly challenging research
field because of the ill-defined nature and large molecu-
lar sizes of this family of molecules.
In teas, it is generally accepted that the beneficial
properties are derived from the polyphenolic components.
However, their chemical nature varies according to the
post-harvest processing to which the tea leaves are sub-
jected, and it is only the GTP that has been studied in
detail. Nevertheless, the antioxidant properties of green
and black tea are similar [62], and epidemiological stud-
ies suggest that their beneficial health effects are also
similar [43,44]. Furthermore, teas also contain other
bioactive molecules, such as theanine, and also some as
yet unidentified molecules with the ability to chelate
metal ions such as Cu(II) at very low pH values [46,61].
As described in this paper, EPR spectroscopy is able to
make appreciable contributions to developing our under-
standing of free radical aspects of the chemistry of coffee
and teas. However, this approach to the research is still in
its infancy and more progress is expected in the near
future from further applications of the technique.

B. A. Goodman et al. / Agricultural Sciences 4 (2013) 433-442 439
Firstly, EPR provides an opportunity to investigate in
real time the formation and reaction of free radicals dur-
ing the roasting process. However, as yet few studies
have been performed, and more investigations are needed
to understand the influence of various factors such as
plant genetics, bean age, roasting temperature profiles,
gas flow rates, water contents of the green beans, etc. In
addition, such measurements should be combined with or
related to parallel measurements of the emission of vola-
tile organic compounds, as reported by Dorfner et al.
[63,64] and Wieland et al., [65] using on-line Proton-
Transfer-Reaction Mass-Spectrometry.
Further investigations of the relative importance of
various environmental factors on the changes that occur
during the storage of roasted coffees are still needed,
because the various studies that have been reported to
date have been based on relatively small data sets. Con-
sidering the large differences in free radical generation
observed by Goodman et al. [21] for individual beans
during a batch roasting of a blend of coffee beans of dif-
ferent origin, it also seems possible that there could be
correspondingly large differences in the behavior of dif-
ferent types of bean during storage.
Understanding the solution chemistry of both coffee
and tea beverages is a long-standing problem, and al-
though progress is being made there is still much that
remains unknown. With both beverages, oxidation proc-
esses originating from exposure to O2 result in progres-
sive alteration of the beverages. It seems likely that Fen-
ton reaction chemistry plays an important role, and be-
cause of the highly reactive nature of the hydroxyl radi-
cal, antioxidants and/or free radical scavengers are inef-
fective in inhibiting its reactions. Thus the most effective
approach to stability of solutions of these beverages
would appear to be strict exclusion of O2 at various criti-
cal stages of their preparation. Recent preliminary results
[33,34] suggest that may be the case for coffee, but more
detailed studies on teas are still required.
Also with teas, further measurements are required on
red and black teas in order to relate details of their
chemistry to that of green tea, which has been studied in
much greater detail. This should not just address the
chemistry of the polyphenols, but should also consider
the identity and reactions of other low molecular weight
molecules that could contribute to the bioactivity of the
beverage.
11. ACKNOWLEDGEMENTS
Many of the EPR results used in this paper were obtained with facili-
ties at either the Scottish Crop Research Institute or the Austrian Insti-
tute of Technology who are gratefully acknowledged. In addition, the
Nestlé Research Center (NRC) is thanked for supplying and preparing
the liquid coffee specimens. Finally, we wish to recognize the valuable
contributions made by Drs Ederlinda C. Pascual, Katharina F. Pirker
and Joyce Ferreira Severino in developing the original scientific meas-
urements.
REFERENCES
[1] Pulido, R., Hernández-García, M. and Saura-Calixto, F.
(2003) Contribution of beverages to the intake of lipo-
philic and hydrophilic antioxidants in the Spanish diet.
European Journal of Clinical Nutrition, 57, 1275-1282.
doi:10.1038/sj.ejcn.1601685
[2] Svilaas, A., Kaur Sakhi, A., Frost Andersen, L., Svilaas,
T., Ström, E.C., Jacobs Jr., D.R. Ose, L. and Blomhoff , R.
(2004) Intakes of antioxidants in coffee, wine, and
vegetables are correlated with plasma carotenoids in
humans. Journal of Nutrition, 134, 562-567.
[3] Stadler, R.H. and Fay, L.B. (1995) Antioxidative reac-
tions of caffeine: Formation of 8-oxocaffeine (1,3,7-
trimethyluric acid) in coffee subjected to oxidative stress.
Journal of Agricultural and Food Chemistry, 43, 1332-
1338. doi:10.1021/jf00053a038
[4] Zhao, Y.K., Cao, Q.E., Liu, H.T., Wang, K.T., Yan, A.X.
and Hu, Z.D. (2000) Determination of baicalin,
chlorogenic acid and caffeic acid in traditional Chinese
medicinal preparations by capillary zone electrophoresis.
Chromatographia, 51, 483-486.
doi:10.1007/BF02490489
[5] Chen, X.F., Zhang, J.U., Xue, C.X., Chen, X.G. and Hu,
Z.D. (2004) Simultaneous determination of some active
ingredients in anti-viral preparations of traditional
Chinese medicine by micellar electrokinetic chroma-
tography. Biomedical Chromatography, 18, 673-680.
doi:10.1002/bmc.373
[6] Higdon, J.V. and Frei, B. (2006) Coffee and health: A
review of recent human research. Critical Reviews in
Food Science and Nutrition, 46, 101-123.
doi:10.1080/10408390500400009
[7] Clifford, M.N. (1999) Chlorogenic acids and other cin-
namates—Nature, occurrence and dietary burden. Journal
of the Science of Food and Agriculture, 79, 362-372.
doi:10.1002/(SICI)1097-0010(19990301)79:3<362::AID-
JSFA256>3.0.CO;2-D
[8] Clifford, M.N. (2000) Chlorogenic acids and other cin-
namates—Nature, occurrence, dietary burden, absorption
and metabolism. Journal of the Science of Food and Ag-
riculture, 80, 1033-1043.
doi:10.1002/(SICI)1097-0010(20000515)80:7<1033::AI
D-JSFA595>3.0.CO;2-T
[9] Kuhnert, N. and Jaiswal, R. (2012) Occurrence and iden-
tification of chlorogenic acids in green and roasted coffee
beans. In: Goodman, B.A., Ed., Coffee Consumption and
Health, Nova Science Publishers, New York, 65-97.
[10] Powrie, W.D., Wu, C.H. and Molund, V.P. (1986)
Browning reaction systems as sources of mutagens and
antimutagens. Environmental Health Perspectives, 67,
47-54. doi:10.1289/ehp.866747
[11] Kitts, D.D., Wu, C.H., Kopec, A. and Nagasawa, T. (2006)
Chemistry and genotoxicity of caramelized sucrose.
Molecular Nutrition & Food Research, 50, 1180-1190.
doi:10.1002/mnfr.200600181

B. A. Goodman et al. / Agricultural Sciences 4 (2013) 433-442
440
[12] Casal, S. (2012) Coffee roasting; Accurate control for
increased bioactivity. In Goodman, B.A., Ed., Coffee
Consumption and Health, Nova Science Publishers, New
York, 99-119.
[13] Yanagimoto, K., Lee, K.G., Ochi, H. and Shibamoto, T.
(2002) Antioxidative activity of heterocyclic compounds
found in coffee volatiles produced by Maillard reaction.
Journal of Agricultural and Food Chemistry, 50, 5480-
5484. doi:10.1021/jf025616h
[14] Obana, H., Nakamura, S. and Tanaka, R. (1986) Suppres-
sive effects of coffee on the SOS responses induced by
UV and chemical mutagens. Mutation Research Letters,
175, 47-50. doi:10.1016/0165-7992(86)90124-7
[15] Malaveille, C., Hautefeuille, A., Pignatelli, B., Talaska, G.,
Vineis, P. and Bartsch, H. (1996) Dietary phenolics as
anti-mutagens and inhibitors of tobacco-related DNA
adduction in the urothelium of smokers. Carcinogenesis,
17, 2193-2200. doi:10.1093/carcin/17.10.2193
[16] Perrone, D., Farah, A. and Donangelo, C.M. (2012) In-
fluence of Coffee Roasting on the Incorporation of Phe-
nolic Compounds into Melanoidins and Their Relation-
ship with Antioxidant Activity of the Brew. Journal of
Agricultural and Food Chemistry, 60, 4265-4275.
doi:10.1021/jf205388x
[17] Del Castillo, M.D., Ames, J.M. and Gordon, M.H. (2002)
Effect of roasting on the antioxidant activity of coffee
brews. Journal of Agricultural and Food Chemistry, 50,
3698-3703. doi:10.1021/jf011702q
[18] Sacchetti, G., Di Mattia, C., Pittia, P. and Mastrocola, D.
(2009) Effect of roasting degree, equivalent thermal ef-
fect and coffee type on the radical scavenging activity of
coffee brews and their phenolic fraction. Journal of Food
Engineering, 90, 74-80.
doi:10.1016/j.jfoodeng.2008.06.005
[19] O’Meara, J.P., Truby, F.K. and Shaw, T.M. (1957) Free
radicals in roasted coffee. Food Research, 22, 96-101.
doi:10.1111/j.1365-2621.1957.tb16988.x
[20] Nebesny, E. and Budryn, G. (2006) Changes in free radi-
cals content in coffee beans throughout convective roast-
ing and microwaving and during storage. Deutsche Le-
bensmittel-Rundschau, 102, 526-530.
[21] Goodman, B.A., Pascual, E.C. and Yeretzian, C. (2011)
Real-time monitoring of free radical processes during the
roasting of coffee beans using electron paramagnetic
resonance spectroscopy. Food Chemistry, 125, 248-254.
doi:10.1016/j.foodchem.2010.07.072
[22] Pascual, E.C., Yeretzian, C., Pirker, K.F. and Goodman,
B.A. (2005) Antioxidant, pro-oxidant and free radical
processes in coffee. In: Zhao, B., Liu, G. and Packer, L.,
Eds., Natural Antioxidants and Micronutrients, Me-
dimond, Bologna, 119-125.
[23] Nicoli, M.C., Innocente, N., Pittia, P. and Lerici, C.R.
(1993) Staling of roasted coffee: Volatile release and oxi-
dation reactions during storage. ASIC 15th International
Scientific Colloquium on Coffee, 15, 557-566.
[24] Vila, M.A., Andueza, S., Paz de Peña, M. and Cid, C.
(2005) Fatty acid evolution during the storage of ground,
roasted coffees. Journal of the American Oil Chemists’
Society, 82, 639-646.
[25] Nicoli, M., Calligaris, S. and Manzocco, L. (2009) Shelf-
life testing of coffee and related products: Uncertainties,
pitfalls, and perspectives. Food Engineering Reviews, 1,
159-168. doi:10.1007/s12393-009-9010-8
[26] Yeretzian, C., Pascual, E.C. and Goodman, B.A. (2012)
Effect of roasting conditions and grinding on free radical
contents of coffee beans stored in air. Food Chemistry,
131, 811-816. doi:10.1016/j.foodchem.2011.09.048
[27] Baesso, M. L., Da Silva, E. C., Vargas, H., Cortez, J. G.
and Pelzl, J. (1990). Use of electron spin resonance for
the determination of staling of roast coffee in polyethyl-
ene bag packs. Zeitschrift für Lebensmittel-Untersuchung
und Forschung A, 191, 24-27.
doi:10.1007/BF01202360
[28] Winterbourn, C.C. (1995) Toxicity of iron and hydrogen
peroxide: the Fenton reaction. Toxicology Letters, 82-83,
969-974. doi:10.1016/0378-4274(95)03532-X
[29] Pascual, E.C., Goodman, B.A. and Yeretzian, C. (2002)
Characterisation of free radicals in soluble coffee by
electron paramagnetic resonance spectroscopy. Journal of
Agricultural and Food Chemistry, 50, 6114-6122.
doi:10.1021/jf020352k
[30] Hofmann, T., Bors, W. and Stettmaier, K. (1999) Studies
on radical intermediates in the early stage of the nonen-
zymatic browning reaction of carbohydrates and amino
acids. Journal of Agricultural and Food Chemistry, 47,
379-390. doi:10.1021/jf980626x
[31] Öbinger, C., Burner, U. and Ebermann, R. (1997) Gen-
eration of hydrogen peroxide by plant peroxidases medi-
ated thiol oxidation. Phyton, 37, 219-226.
[32] Buettner, G.R. and Mason, R.P. (1990) Spin-trapping
methods for detecting superoxide and hydroxyl free radi-
cals in vitro and in vivo. In: Packer, L. and Glazer, A.N.,
Eds., Oxygen Radicals in Biological Systems, Part B,
Oxygen Radicals and Antioxidants (Methods in Enzy-
mology, Vol. 186), Academic Press, Inc., San Diego,
127-133.
[33] Pascual, E.C., Yeretzian, C. and Goodman, B.A. (2013)
Probing free radical processes during storage of extracts
from whole roasted coffee beans: Impact of O2 exposure
during extraction and storage. Journal of Agricultural and
Food Chemistry (submitted for publication).
[34] Yeretzian, C., Pascual, E.C. and Goodman, B.A. (2013).
Effects of O2 during various processing steps on free
radical concentrations in hot aqueous extracts of R&G
coffee and their changes during storage. Proceedings of
the PACCON International Conference, Bangsaen (ac-
cepted for publication).
[35] Grosch, W. (2001) Chemistry III: Volatile compounds. In:
Clark, R.J. and Vitzthum, O.G., Eds., Coffee: Recent De-
velopments, Blackwell Science, Oxford, 68-89.
[36] Blank, I., Pascual, E.C., Devaud, S., Fay, L.B., Stadler,
R.H., Yeretzian, C. and Goodman, B.A. (2002) Degrada-
tion of the coffee flavor compound furfuryl mercaptan in
model Fenton-type reaction systems. Journal of Agricul-
tural and Food Chemistry, 50, 2356-2364.
doi:10.1021/jf011329m
[37] Munro, L.J., Curioni, A., Andreoni, W., Yeretzian, C. and

B. A. Goodman et al. / Agricultural Sciences 4 (2013) 433-442 441
Watzke, H. (2003) The elusiveness of coffee aroma: New
insights from a non-empirical approach. Journal of Agri-
cultural and Food Chemistry, 51, 3092-3096.
doi:10.1021/jf0261607
[38] Ho, C.-T. and Zhu, N. (2000). The chemistry of tea. In:
Parliament, Ho, C.-T. and Schieberle, P., Eds., Caffein-
ated Beverages, Health Benefits, Physiological Effects,
and Chemistry, ACS Symposium Series 754, ACS,
Washington DC, 316-326.
doi:10.1021/bk-2000-0754.ch032
[39] Yang, C.S. (1997) Inhibition of carcinogenesis by tea.
Nature, 389, 134-135. doi:10.1038/38154
[40] Mukhtar, H. and Ahmad, N. (2000) Tea polyphenols:
prevention of cancer and optimizing health. American
Journal of Clinical Nutrition, 71, 1698S-1702S.
[41] Hara, Y. (2004) Green tea: Health benefits and applica-
tions. Marcel Dekker Inc., New York.
[42] Hodgson, J.M. (2008) Tea flavonoids and cardiovascular
disease. Asia Pacific Journal of Clinical Nutrition, 17,
288-290.
[43] Katiyar, S.K. and Mukhtar, H. (1996) Tea in chemopre-
vention of cancer: Epidemiologic and experimental stud-
ies. International Journal of Oncology, 8, 221-238.
[44] Vinson, J.A., Teufel, K. and Wu, N. (2004) Green and
black teas inhibit atherosclerosis by lipid, antioxidant,
and fibrinolytic mechanisms. Journal of Agricultural and
Food Chemistry, 52, 3661-3665.
doi:10.1021/jf035255l
[45] Pirker, K.F., Ferreira Severino, J., Reichenauer, T.G. and
Goodman, B.A. (2008) Free radical processes in green tea
polyphenols (GTP) investigated by electron paramagnetic
resonance (EPR) spectroscopy. Biotechnology Annual
Review, 14, 349-401.
doi:10.1016/S1387-2656(08)00013-6
[46] Goodman, B.A., Ferreira Severino, J., Reichenauer, T.G.
and Pirker, K.F. (2009) Aspects of the antioxidant chem-
istry of teas investigated by electron paramagnetic reso-
nance (EPR) spectroscopy. In: Winyayong, P., Syers, J.K.
and Theppakorn, T., Eds., Tea Production and Tea Prod-
ucts, Mae Fah Luang University, Chiang Rai, 101-117.
[47] Ferreira-Severino, J., Goodman, B.A., Kay, C.W.M.,
Stolze, K., Tunega, D., Reichenauer, T.G. and Pirker, K.F.
(2009) Free radicals generated during oxidation of green
tea polyphenols: Electron paramagnetic resonance spec-
troscopy combined with density functional theory calcu-
lations. Free Radical Biology and Medicine, 46, 1076-
1088. doi:10.1016/j.freeradbiomed.2009.01.004
[48] Taguri, T., Tanaka, T. and Kouno, I. (2004) Antimicrobial
activity of 10 different plant polyphenols against bacteria
causing food-borne disease. Biological and Pharmaceu-
tical Bulletin, 27, 1965-1969. doi:10.1248/bpb.27.1965
[49] Moreno, S., Scheyer, T., Romano, C.S. and Vojnov, A.A.
(2006) Antioxidant and antimicrobial activities of rose-
mary extracts linked to their polyphenol composition.
Free Radical Research, 40, 223-231.
doi:10.1080/10715760500473834
[50] Oliveira, I., Sousa, A., Ferreira, I.C.F.R., Bemto, A.,
Estevinho, L. and Pereira, J.A. (2008) Total phenols, an-
tioxidant potential and antimicrobial activity of walnut
(Juglans regia L.) green husks. Food and Chemical
Toxicology, 46, 2326-2331. doi:10.1016/j.fct.2008.03.017
[51] Ksouri, R., Falleh, H., Megdiche, W., Trabelsi, N.,
Mhamdi, B., Chaieb, K.,Bakrouf, A., Magné, C., Abdelly,
C. (2009) Antioxidant and antimicrobial activities of the
edible medicinal halophyte Tamarix gallica L. and related
polyphenolic constituents. Food and Chemical Toxicol-
ogy, 47, 2083-2091. doi:10.1016/j.fct.2009.05.040
[52] Yaltirak, T., Aslim, B., Ozturk, S. and Alli, H. (2009)
Antimicrobial and antioxidant activities of Russula delica
Fr. Food and Chemical Toxicology, 47, 2052-2056.
doi:10.1016/j.fct.2009.05.029
[53] Cartwright, R.A., Roberts, E.A.H. and Wood, D.J. (1954)
Theanine an amino acid of N-ethyl amide present in tea.
Journal of the Science of Food and Agriculture, 5, 597-
599. doi:10.1002/jsfa.2740051208
[54] Kato, M., Gyoten, Y., Sakai-Kato, K. and Toyo’oka, T.
(2003) Rapid analysis of amino acids in Japanese green
tea by microchip electrophoresis using plastic microchip
and fluorescence detection. Journal of Chromatography A,
1013, 183-189. doi:10.1016/S0021-9673(03)01037-9
[55] Kimura, K., Ozeki, M., Juneja, L. and Ohira, H. (2007)
L-Theanine reduces psychological and physiological
stress responses. Biological Psychology, 74, 39-45.
doi:10.1016/j.biopsycho.2006.06.006
[56] Park, S.K., Jung, I.C., Lee, W.K., Lee, Y.S., Park, H.K.,
Go, H.J., Kim, K., Lim, N.K., Hong, J.T., Ly, S.Y. and
Rho, S.S. (2011) A combination of green tea extract and
l-theanine improves memory and attention in subjects
with mild cognitive impairment: A double-blind placebo-
controlled study. Journal of Medicinal Food, 14, 334-
343. doi:10.1089/jmf.2009.1374
[57] Kakuda, T. (2011) Neuroprotective effects of theanine
and its preventive effects on cognitive dysfunction.
Pharmacological Research, 64, 162-168.
doi:10.1016/j.phrs.2011.03.010
[58] Mandel, S., Amit, T., Reznichenko, L., Weinreb, O. and
Youdim, M.B.H. (2006) Green tea catechins as brain-
permeable, natural iron chelators-antioxidants for the
treatment of neurodegenerative disorders. Molecular Nu-
trition & Food Research, 50, 229-234.
doi:10.1002/mnfr.200500156
[59] Pirker, K.F., Baratto, M.C., Basosi, R. and Goodman, B.A.
(2012) Influence of pH on the speciation of copper(II) in
reactions with the green tea polyphenols, epigallocatechin
gallate and gallic acid. Journal of Inorganic Biochemistry,
112, 10-16. doi:10.1016/j.jinorgbio.2011.12.010
[60] Ferreira-Severino, J., Goodman, B.A., Reichenauer, T.G.
and Pirker, K.F. (2011) Is there a redox reaction between
Cu(II) and gallic acid? Free Radical Research, 45, 123-
132. doi:10.3109/10715762.2010.515220
[61] Goodman, B.A., Ferreira Severino, J. and Pirker, K.F.
(2012). Reactions of green and black teas with Cu(II).
Food & Function, 3, 399-409. doi:10.1039/c1fo10086f
[62] Leung, L. K., Su, Y., Chen, R., Zhang, Z., Huang, Y. and
Chen, Z.-Y. (2001) Theaflavins in black tea and catechins
in green tea are equally effective antioxidants. Journal of

B. A. Goodman et al. / Agricultural Sciences 4 (2013) 433-442
442
Nutrition, 131, 2248-2251.
[63] Dorfner, R., Ferge, T., Kettrup, A., Zimmermann, R. and
Yeretzian, C. (2003) Real-time monitoring of 4-vinyl-
guaiacol, guaiacol and phenol during roasting by resonant
laser ionisation time-of-flight mass-spectrometry. Journal
of Agricultural and Food Chemistry, 51, 5768-5773.
doi:10.1021/jf0341767
[64] Dorfner, R., Ferge, T., Yeretzian, C., Kettrup, A. and
Zimmermann, R. (2004) Laser mass spectrometry as
on-line sensor for industrial process analysis: Process
control of coffee roasting. Analytical Chemistry, 76,
1386-1402. doi:10.1021/ac034758n
[65] Wieland, F., Gloess, A.M., Keller, M., Wetzel, A., Schen-
ker, S. and Yeretzian, C. (2012) On-line monitoring of
coffee roasting by proton-transfer-reaction time-of-flight
mass-spectrometry (PTR-ToF-MS): Towards a real-time
process control for a consistent roast profile. Analytical
and Bioanalytical Chemistry, 402, 2531-2543.
doi:10.1007/s00216-011-5401-9