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Quality assessment of coffee beans with ESR and Gamma-ray irradiation
0883-2889/89$3.00+ 0.00 Copyright ~ 1989PergamonPress pie
Appl. Radiat. 1sot. Vol. 40, No. 10-12, pp. 1219-1222, 1989 Int. J. Radiat. Appl. Instrum. Part A Printed in Great Britain. All rights reserved
Quality Assessment of Coffee Beans with ESR and Gamma-ray Irradiation M O T O J I I K E Y A , 1 F O L H O O. B A F F A 2 a n d S E R G I O M A S C A R E N H A S 3 ~Physics Department, Faculty of Science, Osaka University, Toyonaka, Osaka 560, Japan, 2Universidade de Sao Paulo, Faculdade de Filosofia, Ciencias de Ribeirao Preto, "Campus" de Ribeirao Preto, Av. dos Bandeirantes S/N, 14100-Ribeirao Preto, Silo Paulo, Brazil and 3Institute of Physics and Chemistry, University of Silo Paulo at S,~o Carlos, Silo Carlos, Silo Paulo, Brazil Peroxy radical formation in raw coffee beans of different qualities and origins from all over the world has been studied with electron spin resonance (ESR) analysis. The y-ray equivalent absorbed dose (ED) which creates the same concentration of radicals is obtained by the additive ),-ray irradiation of the coffee beans. The ED and the cup quality is somewhat inversely related suggesting that the peroxidation of the unsaturated fatty acid is somewhat indicative of the degree of the aromatic decomposition and rancidity.
1. Introduction
Physical and chemical studies of coffee beans have been made extensively in agriculture for genetic selection of coffee beans, to improve the quality and disease resistance (Amorim and Silva, 1974). Among physical methods, nuclear magnetic resonance (NMR) is the most striking for biological application. Electron spin resonance (ESR) analysis of peroxidizing reactions in protein and amino acids and in dried vegetables and tea leaves has also been studied, and also has been used for testing radical formation in fried potato-chips (Ikeya and Miki, 1980). Interaction of peroxidizing methyl tinoleate with proteins and amino acids in a lipid-protein system produces the same radicals as ionizing radiation (Karel et al., 1975). It has been shown that the concentration of radicals with unpaired electrons seems to have some correlation with the quality or taste, although it depends on the age, humidity, treatment and origin or species. We report here a quality assessment of coffee beans with ESR spectrometry and introduce a concept of equivalent dose (ED), which indicates a degree of organic decomposition or oxidation in the total amount of the organic materials. The ED is obtained by ~,-ray irradiation of coffee beans and observing the enhancement of the radical concentration and ED evaluation. The procedures have also been used in dating of archaeological materials with thermoluminescence and also with ESR (Ikeya, 1986). 2. Experimental
Several types of coffee beans with different caffeine contents and bean oil were supplied by the University of Campifias in Brazil and by the Coffee Import A.R.L40~10-t2--AA
Branch of the Marubeni Food Corporation. Some green yellow, red and brown coffee bean nuts were taken directly from coffee trees on a farm at S5o Paulo to assure the uniform age of beans after the harvest. Beans are kept in a desiccator with silica gels to maintain nearly equal moisture content in the bean. ESR spectrometers (JES-FE and Varian) with 100kHz field modulation were used to assess the relative content of the radicals. 3. Results and Discussion
Figure ! shows a typical ESR spectrum or the derivative line of the microwave absorption as a function of the external magentic field. The broad signal and the 6 derivative lines indicated in the figure are associated with paramagnetic ions of Mn 2+ with the electronic configuration of d5(655/2), split by the hyperfine interaction with the nuclear spin of the manganese (I = 5/2). The ESR signal of the radicals is indicated in the figure. It has been made clear that radicals in some fried foods like potato-chips or instant noodles are produced by the oxidation or decomposition of food oils, Unsaturated fatty acid is peroxidized to give peroxy radicals which further react to the decomposition of the lipid. The manufactured age of fried foods has been determined roughly by observing the enhancement of the ESR signal intensity day by day, and by fitting the results to the equation l ( t ) = Io(l + t / T )
(1)
where t is the time (days) after the initial measurements, Tis the age and I0 and l ( t ) are respectively the signal intensities at the initial and the time after t days (Ikeya and Miki, 1980).
1219
1220
MOTOJI IKEYA et al. Table 1. Coffee quality and ESR signal intensity of coffee beans and ED Variety
Oil content
Caffeine
Cup graded
S,R*
S(Mn)/R*
ED(Gy)
Coffee Arabica cr Arabica 2. cr Catuai Vermelho 3. I C A T U H-3851-4 C1478 4. I C A T U H3849-14-3 5. Coffee C a n e p h o v a (Angola) 6. Coffee Canephova (Guarini) 7. Coffee Canephova
15%
I.I %
Best
< 0.0025
0.044
< 0.8
15%
1.1%
Best
<0.0025
0.045
< 1.8
12%
1.4%
Good
0.010
0.0885
3.8
12%
1.4%
Good
0.016
0.088
6
10%
2.2%
Lower
0.049
0,135
13
10%
2.2%
Lower
0.063
0.050
15
10%
2.2%
Lower
0.057
0.040
20
Vey low
0.056
0.034
23
I.
(cr Robusta) col 10 8. CoffeeRacemosa
*The intensity is normalized to that of the standard sample signal of a ruby, R.
More precisely, the growth behavior involves, to a certain extent, the higher order terms to t. The exact solution of the peroxidizing reaction is made to estimate the age of archaeological and historical materials. The estimated age based on equation (1) is usually older than the real age due to the tendency for growth saturation. The same procedures can be applied to estimate the age of coffee beans. The variation of temperature and the drying procedure under sunlight also make it difficult to estimate the age from the ESR signal intensity since chemical processes are the main factors in radical formation. However, in spite of these difficulties, the apparent difference is clear from the behavior of the signal intensity as a function of time. Enhancement of the radical signal is observed by artificial 7-ray irradiation, as shown in Fig. 2: the ionizing radiation produces radicals similar to those produced by chemical decomposition. One can apply the equivalent radiation dose (ED) which adds the same amount of radicals as the initial dose. The equivalent dose (ED) is the radiation absorbed dose that the bean was exposed to if all radicals had been
produced by 7-irradiation, although the chemical reaction of peroxidization is the main cause of the radical formation. The concentration of radicals after the irradiation to a dose of Q By (1 G y = l J/kg = 100 rad) C(Q) may be expressed as a function of the initial concentration Co and ED. Assuming the proportionality relation,
C(Q)/Co =
(ED + Q)/ED
C(Q) =
C0(1 + Q/ED).
Coffee bean
MR 2÷ I
/,i
l
I
I
I
I
t
(3)
ED is obtained from the growth of the ESR signal intensity by extrapolating the linear part. Classification of coffee beans is a difficult and professional task based on several rules and much experience. The quality of coffee beans depends on taste which is difficult to express scientifically. The relationship between polyphenol oxidase activity and the quality of the beverage has been studied extensively. We have measured about 50 varieties of coffee beans and obtained an ED of 4 different
Rub' , std.
1
(2)
or
I
I
I
i
I
I 550
300
I
J
t
r
I 400
M o g n e t i c f i e l d (roT)
Fig. I. ESR spectrum of a dried coffee bean. In addition to the broad sextet associated with Mn2÷, the signals of lipid peroxy radicals are observed. The standard signal of ruby is also indicated at the low field.
Quality assessment of coffee beans
Signal (spins/g) Coffee quoLity
ED(Gyl
Ri0
x 10-~s //
SLope (10 ~3 spins/g Gy)
+ 36+2
10_+ 1
Stieht.Rio.. 34+2
9 +-1
Soft
1221
~ 11+-2
15
27+I
~
~/
/
10
/I
-30
/
f
-15
I
I
I
0
15
30
.
Dose ( G y l
Fig. 2. The relationship between ESR signal intensity of some coffee beans vs additive ),-ray dose. The extrapolation of the linear enhancement to the zero ordinate left of the origin gives an ED that is the radiation absorbed dose required to create the same number of radicals, as formed by peroxidization reaction.
expert-judged classes of coffee beans as shown in Fig. 3. The E D is small for beans classified by expert grades as good quality. This indicates that the degree of organic decomposition is related with the taste rather than to the absolute magnitude of the radical content. If the content of the bean oil is rich, the content of radicals after a certain time may be higher than that of a bean with a poor quality. However, it will still taste better due to the large amount of unaffected organic material responsible for the taste. Selected black rotten beans show intense E S R signals: coffee made from rotten beans lacks taste and flavor. Hence, the quality of coffee beans can be detected simply with E S R analysis at least relatively from the
Coffee o ED
bean
x S/S(Ruby)
o x/ x
concentration of radicals or more precisely from the ED. The quality naturally becomes reduced since the E D is increased by oxidation. In a paper dealing with the principle o f chemical ESR dating, we have shown that the chemical rate equation can explain the radical formation processes (Ikeya and Miki, 1986). It was demonstrated that the radical concentration reaches a maximum plateau due to the formation and subsequent decay and then decreases as the time proceeds. The decrease is caused by the consumption of the lipid. We can distinguish the stage of the initial formation and the decay stage from the E D and from the time-dependence: the latter shows an apparently larger E D than the initial stage for the same concentration of radicals, and the signal intensity decreases as time elapses. The formation and decay by chemical decomposition as a function of time are given in Fig. 4.
x
/
1.o -~
O
1.0
~
K2/KI. 0
g~ 0.5 -
gl
-
U.I
~b/
0.5
°
0 o
A
I
B
I
C
0.1
I
D
o
Cup grade Fig. 3. The correlation between cup grade and ED. The grade or quality of the coffee beverage can be indicated by the ED.
tilED 11
5
t2IEDz)
10
Kit Fig. 4. The formation and decayof organicradicalsin coffee beans by chemical reaction. The formation rate is K~ and the decay rate is K2 (I/¢). The solution of the rate equation is given as a function of the normalized time. The ED is large at the late stage while it is small at the first stage, for the same concentration of radicals.
1222
MOTOJI IKEYAet al.
Organic radicals are produced by chemical peroxidization of unsaturated fatty acids, or by radiation. A coffee bean consists of outer skin pulp, silver skins and the bean seed. The ESR signal intensity is higher for silver skins than for beans presumably due to the high degree of peroxidation of the bean oil. A coffee bean washed with N a O H solution shows a decrease of ESR signals. This could be due to the oil extraction from the bean. Coffee beans are roasted before grinding. The taste of coffee also depends on the degree of roasting, which is different for different national and individual practices. The present work indicates that the chemical source of the taste and flavor decomposes in coffee beans as it ages, and that ESR signals of radicals, especially the E D value, are somewhat indicative of the degree of decomposition. We are not certain whether or not the radicals are the directly decomposed fragments of the aromatic materials responsible for the taste, or are only indicative of the degree of decomposition of the bean oil, especially in the case of unsaturated fatty acids. However, a simple method of quality determination with E S R analysis would speed up the test at farms studying genetic selection for the improvement of coffee beans. A similar undertaking on quality tests of other crops like corn, beans, nuts and rice could be made with ESR, by measuring the ED. One remark is added here on the use of ESR in archaeology and forensic science. Archaeological beans or corn in pre-lnca days have been studied extensively (Ikeya and Miki, 1986). These archaelogical materials as well as organic substances like mummies and furs could be the subjects of E S R dating using the oxidized signal intensity of Fe 3+ at g = 4.2, rather than the intermediate unstable signal due to organic radicals. Further investigations of historical papers, leathers and furs have been made to demonstrate the feasibility of organic ESR dating and authenticity test. These studies could lead to a " b r e a k t h r o u g h " in ESR dating, from the dating method based on natural radiation damage of minerals and fossils to that utilizing chemical reactions of organic materials and oxidation of transition metal ions like Fe z+ and Cu t, demonstrated for materials in forensic science (Ikeya and Miki, 1985; Miki and Ikeya, 1987; Miki et al., 1985). The preservation and E S R dating of papers were also reported in attempts to improve the conservation of archaeological materials in museums (Ikeya and Miki, 1985). Acknowledgements--The authors wish to thank Professor A. Carvalho at The University of Campenus for his cooperation in supplying us with several coffee bean varieties as
well as valuable information. Coffee beans from sources throughout the world have also been supplied by Marubeni Food Co. in Tokyo. This work is partly supported by a grant from the Research Foundation of the State of Silo Paulo. Brazil and of Scientific Aid from the Japanese Ministry of Education, Science and Culture concerning ESR dosimet~' and dating (62300016).
References Amorim H. V. and Silvia D. M. (1974) Relationship between the polyphenoloxidase activity of coffee beans and the quality of the beverage. Nature 219, 304-308. Amorim A. V. and Amorim V. L. (1977) Coffee enzymes and coffee quality, ACS Symposium No. 47. Enzymes In Food and Beverage Processing (Eds. Ory R. L. and St Angelo A. J.) p. 27. American Chemical Society, Washington, D.C. Amorim H. V., Basso L. C., Crocomo O. J. and Teixeira A. A. (1977) Polyamines in green and roasted coffee. J. Agric. Food Chem. 25, 957-958. Fritsch G., Lopez T. C. and Rodriguez L. J. (1974) Generation and recombination of free radicals in organic materials studied by electron spin resonance. J. Mag. Res. 16, 48-55. Hillman G. C., Robins G. V., Oduwole D., Sales K. D. and McNeil D. A. C. (1985) The use of electron spin resonance spectroscopy to determine the thermal histories of cereal grains. J. Arch. Sci. 12, 49-58. Ikeya M. (1988) Dating and dosimetry with electron spin resonance. Mag. Res. Rev. 13, 91-134. Ikeya M. and Miki T. (1980) A new dating method with a digital ESR dating. Naturwissenschaften 67, 191-192. Ikeya M. and Miki T. (1985a) Principle of chemical ESR dating for organic materials using radical formation. J. Speleol. Soc. Japan. 10, 32 37. Ikeya M. and Miki T. (1985b) ESR dating of organic substance; From potatochips to a dead body. Nucl. Tracks 10, 909-912. Ikeya M. and Miki T. (1985c) ESR dating and preservation of papers. Naturwissenschaften 72, 32 33. Ikeya M. and Miki T. (1986) Organic ESR dating in archaeology. J. Arch. Chem. 4, 1 10. Karel M., Schaich K. and Ramb R. (1975) Interaction of peroxidizing methyl linoleate with some proteins and amino acids. J. Agric. Food Chem. 23, 159-163. Miki T. and Ikeya M. (1987) Electron spin resonance of bloodstrains and its application to the estimation of time after bleeding. Forensic Sci. Int. 35, 149-158. Miki T., Yahagi T., Ikeya M., Sugawara N. and Furuno J. (1985) ESR dating of organic substance: Corpse for forensic medicine. ESR Dating and Dosimetry (Eds Ikeya M. and Miki T.) pp. 447-451. IONICS, Tokyo. O'Meara J. P., Truby F. K. and Shaw T. M. (1957) Free radicals in roasted coffee. Food Technol. !1, 96-100. Singer I.,. S. (1959) Synthetic ruby as a secondary standard for the measurements of intensities in ESR. J. AppL Phys. 30, 1463-1464. Schaich K. M. and Karel M. (1976) Free radical reactions of peroxidizing lipids with amino acids and proteins: An ESR study. Lipids I1, 392-400. Wajda Pins and Walczyk D. (1978) Relation between acid value of extracted fatty matter and age of green coffee beans. J. Sci. Food Agric. 29, 377-380.
Appl. Radiat. 1sot. Vol. 40, No. 10-12, pp. 1219-1222, 1989 Int. J. Radiat. Appl. Instrum. Part A Printed in Great Britain. All rights reserved
Quality Assessment of Coffee Beans with ESR and Gamma-ray Irradiation M O T O J I I K E Y A , 1 F O L H O O. B A F F A 2 a n d S E R G I O M A S C A R E N H A S 3 ~Physics Department, Faculty of Science, Osaka University, Toyonaka, Osaka 560, Japan, 2Universidade de Sao Paulo, Faculdade de Filosofia, Ciencias de Ribeirao Preto, "Campus" de Ribeirao Preto, Av. dos Bandeirantes S/N, 14100-Ribeirao Preto, Silo Paulo, Brazil and 3Institute of Physics and Chemistry, University of Silo Paulo at S,~o Carlos, Silo Carlos, Silo Paulo, Brazil Peroxy radical formation in raw coffee beans of different qualities and origins from all over the world has been studied with electron spin resonance (ESR) analysis. The y-ray equivalent absorbed dose (ED) which creates the same concentration of radicals is obtained by the additive ),-ray irradiation of the coffee beans. The ED and the cup quality is somewhat inversely related suggesting that the peroxidation of the unsaturated fatty acid is somewhat indicative of the degree of the aromatic decomposition and rancidity.
1. Introduction
Physical and chemical studies of coffee beans have been made extensively in agriculture for genetic selection of coffee beans, to improve the quality and disease resistance (Amorim and Silva, 1974). Among physical methods, nuclear magnetic resonance (NMR) is the most striking for biological application. Electron spin resonance (ESR) analysis of peroxidizing reactions in protein and amino acids and in dried vegetables and tea leaves has also been studied, and also has been used for testing radical formation in fried potato-chips (Ikeya and Miki, 1980). Interaction of peroxidizing methyl tinoleate with proteins and amino acids in a lipid-protein system produces the same radicals as ionizing radiation (Karel et al., 1975). It has been shown that the concentration of radicals with unpaired electrons seems to have some correlation with the quality or taste, although it depends on the age, humidity, treatment and origin or species. We report here a quality assessment of coffee beans with ESR spectrometry and introduce a concept of equivalent dose (ED), which indicates a degree of organic decomposition or oxidation in the total amount of the organic materials. The ED is obtained by ~,-ray irradiation of coffee beans and observing the enhancement of the radical concentration and ED evaluation. The procedures have also been used in dating of archaeological materials with thermoluminescence and also with ESR (Ikeya, 1986). 2. Experimental
Several types of coffee beans with different caffeine contents and bean oil were supplied by the University of Campifias in Brazil and by the Coffee Import A.R.L40~10-t2--AA
Branch of the Marubeni Food Corporation. Some green yellow, red and brown coffee bean nuts were taken directly from coffee trees on a farm at S5o Paulo to assure the uniform age of beans after the harvest. Beans are kept in a desiccator with silica gels to maintain nearly equal moisture content in the bean. ESR spectrometers (JES-FE and Varian) with 100kHz field modulation were used to assess the relative content of the radicals. 3. Results and Discussion
Figure ! shows a typical ESR spectrum or the derivative line of the microwave absorption as a function of the external magentic field. The broad signal and the 6 derivative lines indicated in the figure are associated with paramagnetic ions of Mn 2+ with the electronic configuration of d5(655/2), split by the hyperfine interaction with the nuclear spin of the manganese (I = 5/2). The ESR signal of the radicals is indicated in the figure. It has been made clear that radicals in some fried foods like potato-chips or instant noodles are produced by the oxidation or decomposition of food oils, Unsaturated fatty acid is peroxidized to give peroxy radicals which further react to the decomposition of the lipid. The manufactured age of fried foods has been determined roughly by observing the enhancement of the ESR signal intensity day by day, and by fitting the results to the equation l ( t ) = Io(l + t / T )
(1)
where t is the time (days) after the initial measurements, Tis the age and I0 and l ( t ) are respectively the signal intensities at the initial and the time after t days (Ikeya and Miki, 1980).
1219
1220
MOTOJI IKEYA et al. Table 1. Coffee quality and ESR signal intensity of coffee beans and ED Variety
Oil content
Caffeine
Cup graded
S,R*
S(Mn)/R*
ED(Gy)
Coffee Arabica cr Arabica 2. cr Catuai Vermelho 3. I C A T U H-3851-4 C1478 4. I C A T U H3849-14-3 5. Coffee C a n e p h o v a (Angola) 6. Coffee Canephova (Guarini) 7. Coffee Canephova
15%
I.I %
Best
< 0.0025
0.044
< 0.8
15%
1.1%
Best
<0.0025
0.045
< 1.8
12%
1.4%
Good
0.010
0.0885
3.8
12%
1.4%
Good
0.016
0.088
6
10%
2.2%
Lower
0.049
0,135
13
10%
2.2%
Lower
0.063
0.050
15
10%
2.2%
Lower
0.057
0.040
20
Vey low
0.056
0.034
23
I.
(cr Robusta) col 10 8. CoffeeRacemosa
*The intensity is normalized to that of the standard sample signal of a ruby, R.
More precisely, the growth behavior involves, to a certain extent, the higher order terms to t. The exact solution of the peroxidizing reaction is made to estimate the age of archaeological and historical materials. The estimated age based on equation (1) is usually older than the real age due to the tendency for growth saturation. The same procedures can be applied to estimate the age of coffee beans. The variation of temperature and the drying procedure under sunlight also make it difficult to estimate the age from the ESR signal intensity since chemical processes are the main factors in radical formation. However, in spite of these difficulties, the apparent difference is clear from the behavior of the signal intensity as a function of time. Enhancement of the radical signal is observed by artificial 7-ray irradiation, as shown in Fig. 2: the ionizing radiation produces radicals similar to those produced by chemical decomposition. One can apply the equivalent radiation dose (ED) which adds the same amount of radicals as the initial dose. The equivalent dose (ED) is the radiation absorbed dose that the bean was exposed to if all radicals had been
produced by 7-irradiation, although the chemical reaction of peroxidization is the main cause of the radical formation. The concentration of radicals after the irradiation to a dose of Q By (1 G y = l J/kg = 100 rad) C(Q) may be expressed as a function of the initial concentration Co and ED. Assuming the proportionality relation,
C(Q)/Co =
(ED + Q)/ED
C(Q) =
C0(1 + Q/ED).
Coffee bean
MR 2÷ I
/,i
l
I
I
I
I
t
(3)
ED is obtained from the growth of the ESR signal intensity by extrapolating the linear part. Classification of coffee beans is a difficult and professional task based on several rules and much experience. The quality of coffee beans depends on taste which is difficult to express scientifically. The relationship between polyphenol oxidase activity and the quality of the beverage has been studied extensively. We have measured about 50 varieties of coffee beans and obtained an ED of 4 different
Rub' , std.
1
(2)
or
I
I
I
i
I
I 550
300
I
J
t
r
I 400
M o g n e t i c f i e l d (roT)
Fig. I. ESR spectrum of a dried coffee bean. In addition to the broad sextet associated with Mn2÷, the signals of lipid peroxy radicals are observed. The standard signal of ruby is also indicated at the low field.
Quality assessment of coffee beans
Signal (spins/g) Coffee quoLity
ED(Gyl
Ri0
x 10-~s //
SLope (10 ~3 spins/g Gy)
+ 36+2
10_+ 1
Stieht.Rio.. 34+2
9 +-1
Soft
1221
~ 11+-2
15
27+I
~
~/
/
10
/I
-30
/
f
-15
I
I
I
0
15
30
.
Dose ( G y l
Fig. 2. The relationship between ESR signal intensity of some coffee beans vs additive ),-ray dose. The extrapolation of the linear enhancement to the zero ordinate left of the origin gives an ED that is the radiation absorbed dose required to create the same number of radicals, as formed by peroxidization reaction.
expert-judged classes of coffee beans as shown in Fig. 3. The E D is small for beans classified by expert grades as good quality. This indicates that the degree of organic decomposition is related with the taste rather than to the absolute magnitude of the radical content. If the content of the bean oil is rich, the content of radicals after a certain time may be higher than that of a bean with a poor quality. However, it will still taste better due to the large amount of unaffected organic material responsible for the taste. Selected black rotten beans show intense E S R signals: coffee made from rotten beans lacks taste and flavor. Hence, the quality of coffee beans can be detected simply with E S R analysis at least relatively from the
Coffee o ED
bean
x S/S(Ruby)
o x/ x
concentration of radicals or more precisely from the ED. The quality naturally becomes reduced since the E D is increased by oxidation. In a paper dealing with the principle o f chemical ESR dating, we have shown that the chemical rate equation can explain the radical formation processes (Ikeya and Miki, 1986). It was demonstrated that the radical concentration reaches a maximum plateau due to the formation and subsequent decay and then decreases as the time proceeds. The decrease is caused by the consumption of the lipid. We can distinguish the stage of the initial formation and the decay stage from the E D and from the time-dependence: the latter shows an apparently larger E D than the initial stage for the same concentration of radicals, and the signal intensity decreases as time elapses. The formation and decay by chemical decomposition as a function of time are given in Fig. 4.
x
/
1.o -~
O
1.0
~
K2/KI. 0
g~ 0.5 -
gl
-
U.I
~b/
0.5
°
0 o
A
I
B
I
C
0.1
I
D
o
Cup grade Fig. 3. The correlation between cup grade and ED. The grade or quality of the coffee beverage can be indicated by the ED.
tilED 11
5
t2IEDz)
10
Kit Fig. 4. The formation and decayof organicradicalsin coffee beans by chemical reaction. The formation rate is K~ and the decay rate is K2 (I/¢). The solution of the rate equation is given as a function of the normalized time. The ED is large at the late stage while it is small at the first stage, for the same concentration of radicals.
1222
MOTOJI IKEYAet al.
Organic radicals are produced by chemical peroxidization of unsaturated fatty acids, or by radiation. A coffee bean consists of outer skin pulp, silver skins and the bean seed. The ESR signal intensity is higher for silver skins than for beans presumably due to the high degree of peroxidation of the bean oil. A coffee bean washed with N a O H solution shows a decrease of ESR signals. This could be due to the oil extraction from the bean. Coffee beans are roasted before grinding. The taste of coffee also depends on the degree of roasting, which is different for different national and individual practices. The present work indicates that the chemical source of the taste and flavor decomposes in coffee beans as it ages, and that ESR signals of radicals, especially the E D value, are somewhat indicative of the degree of decomposition. We are not certain whether or not the radicals are the directly decomposed fragments of the aromatic materials responsible for the taste, or are only indicative of the degree of decomposition of the bean oil, especially in the case of unsaturated fatty acids. However, a simple method of quality determination with E S R analysis would speed up the test at farms studying genetic selection for the improvement of coffee beans. A similar undertaking on quality tests of other crops like corn, beans, nuts and rice could be made with ESR, by measuring the ED. One remark is added here on the use of ESR in archaeology and forensic science. Archaeological beans or corn in pre-lnca days have been studied extensively (Ikeya and Miki, 1986). These archaelogical materials as well as organic substances like mummies and furs could be the subjects of E S R dating using the oxidized signal intensity of Fe 3+ at g = 4.2, rather than the intermediate unstable signal due to organic radicals. Further investigations of historical papers, leathers and furs have been made to demonstrate the feasibility of organic ESR dating and authenticity test. These studies could lead to a " b r e a k t h r o u g h " in ESR dating, from the dating method based on natural radiation damage of minerals and fossils to that utilizing chemical reactions of organic materials and oxidation of transition metal ions like Fe z+ and Cu t, demonstrated for materials in forensic science (Ikeya and Miki, 1985; Miki and Ikeya, 1987; Miki et al., 1985). The preservation and E S R dating of papers were also reported in attempts to improve the conservation of archaeological materials in museums (Ikeya and Miki, 1985). Acknowledgements--The authors wish to thank Professor A. Carvalho at The University of Campenus for his cooperation in supplying us with several coffee bean varieties as
well as valuable information. Coffee beans from sources throughout the world have also been supplied by Marubeni Food Co. in Tokyo. This work is partly supported by a grant from the Research Foundation of the State of Silo Paulo. Brazil and of Scientific Aid from the Japanese Ministry of Education, Science and Culture concerning ESR dosimet~' and dating (62300016).
References Amorim H. V. and Silvia D. M. (1974) Relationship between the polyphenoloxidase activity of coffee beans and the quality of the beverage. Nature 219, 304-308. Amorim A. V. and Amorim V. L. (1977) Coffee enzymes and coffee quality, ACS Symposium No. 47. Enzymes In Food and Beverage Processing (Eds. Ory R. L. and St Angelo A. J.) p. 27. American Chemical Society, Washington, D.C. Amorim H. V., Basso L. C., Crocomo O. J. and Teixeira A. A. (1977) Polyamines in green and roasted coffee. J. Agric. Food Chem. 25, 957-958. Fritsch G., Lopez T. C. and Rodriguez L. J. (1974) Generation and recombination of free radicals in organic materials studied by electron spin resonance. J. Mag. Res. 16, 48-55. Hillman G. C., Robins G. V., Oduwole D., Sales K. D. and McNeil D. A. C. (1985) The use of electron spin resonance spectroscopy to determine the thermal histories of cereal grains. J. Arch. Sci. 12, 49-58. Ikeya M. (1988) Dating and dosimetry with electron spin resonance. Mag. Res. Rev. 13, 91-134. Ikeya M. and Miki T. (1980) A new dating method with a digital ESR dating. Naturwissenschaften 67, 191-192. Ikeya M. and Miki T. (1985a) Principle of chemical ESR dating for organic materials using radical formation. J. Speleol. Soc. Japan. 10, 32 37. Ikeya M. and Miki T. (1985b) ESR dating of organic substance; From potatochips to a dead body. Nucl. Tracks 10, 909-912. Ikeya M. and Miki T. (1985c) ESR dating and preservation of papers. Naturwissenschaften 72, 32 33. Ikeya M. and Miki T. (1986) Organic ESR dating in archaeology. J. Arch. Chem. 4, 1 10. Karel M., Schaich K. and Ramb R. (1975) Interaction of peroxidizing methyl linoleate with some proteins and amino acids. J. Agric. Food Chem. 23, 159-163. Miki T. and Ikeya M. (1987) Electron spin resonance of bloodstrains and its application to the estimation of time after bleeding. Forensic Sci. Int. 35, 149-158. Miki T., Yahagi T., Ikeya M., Sugawara N. and Furuno J. (1985) ESR dating of organic substance: Corpse for forensic medicine. ESR Dating and Dosimetry (Eds Ikeya M. and Miki T.) pp. 447-451. IONICS, Tokyo. O'Meara J. P., Truby F. K. and Shaw T. M. (1957) Free radicals in roasted coffee. Food Technol. !1, 96-100. Singer I.,. S. (1959) Synthetic ruby as a secondary standard for the measurements of intensities in ESR. J. AppL Phys. 30, 1463-1464. Schaich K. M. and Karel M. (1976) Free radical reactions of peroxidizing lipids with amino acids and proteins: An ESR study. Lipids I1, 392-400. Wajda Pins and Walczyk D. (1978) Relation between acid value of extracted fatty matter and age of green coffee beans. J. Sci. Food Agric. 29, 377-380.