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Effects of roasting temperatures and gamma irradiation on the content of chlorogenic acid, caffeic acid and soluble carbohydrates of coffee
International Journal of Applied Radiation and Isotopes, 1975, Vol. 26, pp. 656-661. Pergamon Press. Printed in Northern Ireland
Effects of Roasting Temperatures and Gamma Irradiation on the Content of Chlorogenic Acid, Caffeic Acid and Soluble Carbohydrates of Coffee* S. N. D E S H P A N D E and A. A. A G U I L A R Puerto Rico Nuclear Center and Department of Chemistry, University of Puerto Rico, Mayaguez, Puerto Rico 00708, U.S.A.
(Received 25 March 1975) Two varieties of Puerto Rican coffee, Coffea canephora L. var. Robusta, and Coffea arabica L. var. Borbon, were subjected to four different doses of radiation and roasted at two different temperatures. Aqueous extracts of the ground coffee beans were analyzed for chlorogenic acid and eaffeic acid at 324 nm and 360 nm wavelength settings, respectively. Samples subjected to the roasting treatments in conjunctiort with irradiation treatments were treated with basic lead acetate prior to the colorimetric analyses in order to eliminate interfering substances. The total carbohydrate content was also determined by colorimetric techniques with anthrone reagent. The total nitrogen content of the pulverized samples was determined by the microKjeldahl method. While roasting treatments caused a reduction in the concentrations of the chlorogenic acid, caffeic acid, and the carbohydrates, the radiation treatments increased the concentrations of soluble carbohydrates without affecting the concentrations of chlorogenic acid or caffeic acid. It therefore appears that radiation treatments seem to cause degradation of the acid-polysaccharide complexes liberating soluble sugars. There were no noticeable changes in the total content of nitrogen caused by roasting or the radiation treatments as indicated by the statistical analysis employing the split plot design. INTRODUCTION ALTHOUOH COFFEE abounds in carbohydrates and several nitrogenous compounds, the phenolic acids in particular quinic acid, caffeic acid and chlorogenic acid, are supposed to be primarily responsible for both the flavor and aroma of coffee. (1.~ Chlorogenic acid is one of the esters of quinic acid and upon hydrolysis yields caffeic acid. ~s) Chlorogenic acid exists in the leaves and seeds of coffee associated with * This paper was prepared in connection with work under contract No. AT-(40-1)-1833 with the U.S. Atomic Energy Commission. The Commission retains a non-exclusive, royalty-free license in and to any copyright covering this paper, with the right to authorize others to reproduce all or any part of the copyrighted paper. This paper is a part of the M.S. Thesis of the second author, University of Puerto Rico, Mayaguez, Puerto Rico.
sugars and proteinacious substances. These complexes are supposed to be responsible for the organoleptic and stimulating effects of coffee besides being protective mechanisms against plant pathogens, t~-6~ Several monosaccharides and complex polysaceharides such as galactosans, glucosans, arabinogalactosans, and mannosans from coffee have also been reported in literature. ~7-9~ The occurrence of nitriles and heterocyclic compounds in coffee is well known. ~1'1°) However, there is no evidence for free amino acids in coffeetl~ and the proteins and their complexes are not well characterized as their isolation is very difficult. ~1'~ The mechanisms of the chemical changes occurring in the process of roasting of coffee are not well established but it is theorized that the pyrolysis of the carbohydrates at temperatures above 100°C results in formation of volatile compounds responsible for the aroma
656
Effects of roasting temperatures and gamma irradiation of coffee. ~9.xo~ T h e p r i m a r y effect of ionizing radiation on the polysaccharides is known to be liberation of monosaccharides or simpler sugars. I t was, therefore, decided to study the possible contribution of ionizing radiation in liberation of sugars or free a m o n o acids from radiolysis of proteins to form Maillard type condensation products, ~x2~ and in liberation of the chlorogenie and eaffeic acids which presumably cause enhancement of flavor. MATERIALS
AND METHODS
Pre~Oaration of coffee extracts Coffee seeds of two local varieties, Goffea eanephora L. var. Robusta and Coffea arabica L. vat. Borbon, were subjected to irradiation at 0.5 Mrad, 1.0 M r a d and 12 Mrad, with a 2,500 Ci source of e°Co. T h e samples were so positioned that the dose rate was approx. 800 rad/min. Unirradiated seeds were used as controls. T h e coffee beans were further weighed and roasted for 10 rain in an a l u m i n u m p a n surrounded b y a heating mantle at 200°C and 250°C, respectively, and weighed again in order to account for the loss in weight caused by formation of volatile compounds. T h e green and roasted coffee beans were ground to pass 60 mesh sieve size with a Wiley mill a n d dried to a constant weight in a v a c u u m oven at 50°C. The extraction procedure reported by Moore, s ~x was slightly modified as follows. A 500 m g sample of the pulverized coffee from each treatment was added to 2 5 0 m l of distilled water in a volumetric flask, and it was held at 80°C in a water b a t h for 20 rain. Later the volume was adjusted to 250 ml and the extract was filtered with sintered glass filters by suction. T h e first 25 mi of the filtrate was discarded and the coffee grounds were saved for further analyses.
The eolorimetric analysis of ehlorogenio acid, eaffeie acid, and the soluble carbohydrates The coloHmetric method reported by MOORES
et al. ~ was partly modified for determination of chlorogenic and caffeic adds. A 3 0 m l aliquot of the coffee extracts was treated with 0.30 g of potassium acetate and 2 ml of saturated basic lead acetate. T h e mixture was heated for 5 rain in a boiling water hath, cooled in an ice bath while the contents were
657
kept agitated for 1 hr with a magnetic stirrer, and filtered with a fluted filter paper. T h e absorbance of these filtrates was measured by means of a Beckman DB spectrophotometer, at 324 n m for chlorogenic acid a n d at 347 n m for caffeic acid. Since other constituents of roasted coffee also absorb at these wavelengths, a 5 ml aliquot of the original extract was diluted to 100 ml and the absorbance of this solution was also measured at the settings of 324 n m and 347 nm. One-tenth of the absorbance of the samples treated with lead acetate was subtraced from the absorbance of the untreated extracts. The total content of the soluble carbohydrates was determined according to the colorimetric procedure after modification of the method of MoRms ~Is~ with stabilized anthrone reagent. T h e original coffee extracts were diluted in the proportion of one to two, and one ml aliquot of this were transferred to 25 m test tubes. T h e tubes were cooled in an ice b a t h and 5 ml of the anthrone reagent was added to each tube. T h e tubes were heated for exactly I 0 min in a boiling water bath and cooled again in an ice bath. T h e absorbance of the color complex developed was measured at 600 n m on the Beckman DB spectrophotometer, and the concentration of the samples was determined by means of a standard curve.
Determination of the nitrogen content of the coffee extracts T h e nitrogen content of the pulverized coffee beans was determined according to the official method o f A . O . A . C . ~14~ A 50 m g sample of the coffee powder, which was sieved with a 60 mesh screen and dried under v a c u u m to constant weight, was transferred to a 2 5 m l miero-Kjeldahl digestion flask. As a catalyst, 0.1 g of K s S O 4 and H g O mixture was added. After addition of 2 ml of concentrated HsSO~, the flasks were heated on electric burners until the contents were digested to a colorless liquid. These were further subjeeted to distillation and titration. All the treatments were replicated three times, and all the analyses for each treatment in turn were m a d e in triplicate. T h e data were subjected to analysis of variance using the split-split plot design. ~15)
658
S. N. Deshpande and A. A. Aguilar TABLE 1. Percentage of chlorogenic acid in coffee C. Cane~hora Dose (Me~arad)
0
O. 5
i0.2 i0.7 11.4
2~ °
--
C. Arabica 1
12
0
O. 5
1
12
ii. 2 ii. 4 11.5
i0.8 ii. 6 11.7
ii. 5 ll. 4 10.9
7.4 8.5 8.4
8.2 8.1 8.9
7.9 7.7 8.6
8.1 8.1 8.5
8.8
8.6
8.4
8.6
8.8
8.7
7.6
9.1
8.4
6.1 6.0 6.1
5.4 5.9 5.1
5.8 6.2 6.1
5.8 6.1 5.3
4.9 4.9 5.0
1.4 1.6 1.5
2.2 2.4 2.2
2.4 2.0 2.4
2.2 1.3 2.l
1.4 1.8 1.4
1.9 1.8 1.9
1.6 1.8 1.8
1.7 1.8 1.9
Roasting Te~erature ('C) Unroasted Green
250__°
RESULTS AND DISCUSSION The roasting treatments seem to cause a decrease in the concentration of chlorogenic acid, compared with concentrations of green coffee (Table 1). The effect of radiation treatments is noticeable at the 12 Mrad level For irradiated samples roasted at 250°C there is a slight increase in the concentration of chlorogenic acid. The analysis of variance for the concentration of chlorogenic acid showed a significant variation for differences in the species of coffee, roasting treatments and radiation doses (Table 6). The effects of the various treatments on caffeic acid are reported in
Table 2. A slight decrease in percent concentration was observed as a result of the roasting temperatures. Caffeic acid seemed to withstand the roasting treatments. The effect of radiation treatment was not so wall defined with respect to caffeic acid. The analysis of variance, does, however, show significant differences in the concentrations of caffeic acid within species, roasting treatments, and radiation doses (Table 6). The roasting treatment manifested up to 8 0 ~ decrease in the concentration of the total carbohydrates (Table 3). This evidenced pyrolysis, and oxidation of the carbohydrates to form volatile
TABLE 2. Percentage of caffeic acid in coffee C. Canephora Dose (Megarad)
0
0.5
C. Arabica 1
12
0
0.5
1
12
Roasting Temperature (°C) Unroasted Green
22.2 23.8 24.4
25.1 24.6 24.2
23.8 25.1 24.2
21.4 21.5 23,0
19.8 23.0 22.3
21.4 23.2 22.8
22.0 23.4 22.7
21.8 21.5 23,4
200°
15.6 16.7 16.6
17.1 18.5 18.3
21.0 20.0 17.3
17.5 17.2 17.3
19,0 19.2 15.8
17,5 17.2 17.6
18.3 18.9 16.7
18.5 18.5 18.7
250°
17.0 17.5 16.6
17.7 19.0 18.3
17.5 19.0 18.0
17.1 17.0 17.1
17.0 16.5 16.6
17.3 18.5 17.7
16.4 18.5 17.5
17.6 17.8 19.0
Effeas of roasting t~mperatures and gamma irradiation
659
TmaLx 3. Percentage of total carbohydrates in coffee C. Canephora
C. Arabica
Dose
(Megarad)
0
0.5
i
12
0
0.5
1
12
9.9 10.7
lO.5 ~.5
lO.3 11.1
11.9 12.o
12.7 14.5
12.5 14.4
12.3 14.3
15.4 15.3
12.1
~.0
10.4
11.7
13.3
13;2
13.6
16.9
Roasting Te~erature (°C) Unroasted Green
200 @ IL
25o__"
4.9 5.9 6.1
5.5 5.5 5.3
4.7 5.0 4.9
5.8 6.0 5.9
5.9 5.7 5.8
5.1 5.5 5.3
5.3 5.9 5.5
5.9 5.8 5.7
2.9 2.5
4.0 3.8
4.0 4.1
3,8 4.2
2.8 2.6
3.8 4.1
3,2 3,7
3.6 3.5
2.5
4.4
4.3
compounds which were released in the process of roasting with the characteristic aroma of coffee (Table 5). Irradiation increased the concentration of the soluble sugars by cleavage of glycosidic linkages of the structural polysaccharides of coffee. T h e effect was pronounced at the radiation dose of 12 Mrad. At the higher roasting temperature of 250°C, an increase in the soluble carbohydrate content was observed at all the doses of radiation. Radiation and the high temperatures of roasting presumably caused degradation of the polysaccharides and the various polysaccharide
4.2
2.5
4.2
3.6
derivatives to simpler sugars, chlorogenic acid and caffeic acid. T h e doses of 0.5 mrad and 1.0 M r a d were not adequate for cleavage of these complex polysaccharides, in green coffee. Perhaps these changes were further accentuated in conjunction with the roasting temperatures. T h e analysis of variance for the soluble carbohydrates showed a significant variation between the species of coffee, roasting temperatures and the radiation doses (Table 6). T h e effect of the various treatments on the nitrogen content are reported in Table 4. There seemed to be no noteworthy changes influenced by
TABLE4. Percentage of nitrogen in coffee C, Arabica
C. Canephora Dose
(Me~arad)
0
0.5
1
2.3 2.9 2.7
3.0 3.2 2.9
3.1 3.2 3.2
200 °
2.8 2.5 2.9
3.0 3.1 3.1
250_ °
3.2 3.3 3.4
3.1 2.6 3.3
12
0
0.5
i
12
2.8 2.7 2.8
2.6 2.7 2.3
2.6 2.7 2.4
2.7 2.7 2.3
2.3 2.1 2.5
3.3 3.2 3.1
3.0 3.2 3.1
2.0 2.6 2.5
2.4 2.6 2.5
2.7 2.7 2.6
2.8 2.3 2.7
3.3 3.3 3.1
3.4 3.1 3.6
2.8 2.7 2.9
2.9 2.8 2.7
2.7 2.8 2.7
3.0 2.6 3.0
Roasting Temperature (°C) Unroasted Green
3.8
S. N. Deshpandeand A. A. Aguilar
660
TABLE 5. ~ moisture content and loss of weight in roasted coffee C. Canephora Dose (Megara~)
C. Arabica
0
0.5
i
12
0
0.5
i
12
10.4
15.0
12.0
11.8
11.4
12.5
11.8
10.3
2OO °
~L.2
12.9
14.6
16.~
15,0
15.5
15.4
19.0
250 °
35.8
29.6
29.3
25.0
35.6
32.8
35.0
32.7
% Humidity: Loss i~ Weight:
ionizing radiation or the roasting temperatures in the nitrogen content. The two different species of coffee seemed to manifest a distinctly different behavior with respect to the content of chlorogenic acid. Coffea arabica had inherently less content of
chlorogenic acid and it was affected most by the roasting treatments. Considering the possibility that caffeic acid can be produced by degradation of chlorogenic acid; a lesser content of caffeic acid in Coffea arabiea even after roasting treatment confirmed the fact that Coffea arabica
TABLE 6. Summary of the statistical analysis for treatments of coffee Serial Number
Compounds Analyzed
F. Values found
F. at 1% tabulated
F at 5% tabulated
Significance
For Dose of Gamma Radiation: i
Total Carbohydrates
20.2
4.4
2.8
++
2
Chlorogenic acid
11.9
4.4
2.8
÷+
3
Caffeic acid
5.1
4.4
2.8
++
1521.5
8.6
4.5
++
For Roasting Temperatures: 1
Total Carbohydrates
2
Chlorogenic acid
688.0
8.6
4.5
++
3
Caffeic acid
188.L
8.6
4.5
++
115.9
98.5
18.5
++
For Varieties of Coffee: i
Total Carbohydrates
2
Chlorogenic acid
38.2
98.5
18.5
++
3
Caffeic acid
33.9
98.5
18.5
++
$++
gigniflcan% at ~ Significant at
Effects of roasting temperatures and gamma irradiation
was affected most by the roasting treatments. T h e behavior of the two varieties cannot be differentiated on chlorogenic acid or caffeic acid with respect to the effects of ionizing radiation. Coffea arabica h a d an initially higher content of the total carbohydrates, and it was, therefore, affected more by both the radiation treatments and the roasting treatments. T a b l e 5 shows the percent loss in weight of coffee seeds after the roasting treatment. CONCLUSIONS T h e radiation dose of 12 M r a d produced simpler compounds by fragmentation of the complex polysaccharides. T h e thermal decomposition of these simpler compounds produced by radiation resulted in volatile compounds responsible for the characteristic flavor. There was no evidence for the existence or liberation of free a m o n o acids or similar nitrogenous compounds by the action of radiation. Thus the possibility of the subsequent tbrmation of the Maillard type condensation products in increased amounts under the influence of high temperatures is perhaps precluded. T h e chlorogenic acid seems to undergo thermal degradation to yield caffeic acid. T h e characteristic flavor of coffee seems to be due to the sugar esters of chlorogenie, and caffeic acids. T h e nitrogenous compounds of coffee withstand the roasting treatments almost entirely.
661
REFERENCES 1. MOORES R. G., DOROTY L. and Wood T. R. Analyt. Chom. 20, 620 (1948). 2. WOLFROM M. L., PLUNKETT R. A. and LAVER M. L. d. agr. Fd Chem. 8~ 58 (1960). 3. POmZNTAJ. V. and BURNS E. E. d. Fd Sci. 36, 490 (1971). 4. HARBORNEJ. B. and CORNERJ. J. Biochem. J. 81, 242 (1961). 5. HASLAM E., MAKmSON G. K. and N A U ~ N M. O. J. Chem. Soc., 2137 (1964). 6. SOSULSKIF. W., So~au~a~ F. S. and Brtha-rv R. S. J. Can. Inst. Fd. TechnoL 5, 101 (1972). 7. WOLFROMM. L., LAVER M. L. and PATIND. L. J. org. Chem. 26, 4533 (1961). 8. WOLVROMM. L. and PATIN D. L. J. agr. Fd Chem. 12, 376 (1964). 9. WoLm~O~ M. L. and PA~N D. L. J. org. Chem. 30, 4060 (1965). 10. MEaarr C. Jr., BAZINETM. L., SULLIVANJ. H. and ROBERTSON D. H. J. agr. Fd Chem. 11, (2), 152 (1963). 11. SMITH A. K. and JOHNSEN V. L. Cereal Chem. 25, 399 (1948). 12. HODOEJ. E. J. agr. Fd Chem. 1, 925 (1953). 13. Mogms D. L. Science 107, 254 (1948). 14. Association of Official Agricultural Chemists. Official Methods of Analysis. Association of Official Agricultural Chemists, Washington, D.C. (1960). 15. SNEDECORA. W. and C o c H ~ W. W. Statistical Methods. The Iowa State University Press, Ames (1971).
Effects of Roasting Temperatures and Gamma Irradiation on the Content of Chlorogenic Acid, Caffeic Acid and Soluble Carbohydrates of Coffee* S. N. D E S H P A N D E and A. A. A G U I L A R Puerto Rico Nuclear Center and Department of Chemistry, University of Puerto Rico, Mayaguez, Puerto Rico 00708, U.S.A.
(Received 25 March 1975) Two varieties of Puerto Rican coffee, Coffea canephora L. var. Robusta, and Coffea arabica L. var. Borbon, were subjected to four different doses of radiation and roasted at two different temperatures. Aqueous extracts of the ground coffee beans were analyzed for chlorogenic acid and eaffeic acid at 324 nm and 360 nm wavelength settings, respectively. Samples subjected to the roasting treatments in conjunctiort with irradiation treatments were treated with basic lead acetate prior to the colorimetric analyses in order to eliminate interfering substances. The total carbohydrate content was also determined by colorimetric techniques with anthrone reagent. The total nitrogen content of the pulverized samples was determined by the microKjeldahl method. While roasting treatments caused a reduction in the concentrations of the chlorogenic acid, caffeic acid, and the carbohydrates, the radiation treatments increased the concentrations of soluble carbohydrates without affecting the concentrations of chlorogenic acid or caffeic acid. It therefore appears that radiation treatments seem to cause degradation of the acid-polysaccharide complexes liberating soluble sugars. There were no noticeable changes in the total content of nitrogen caused by roasting or the radiation treatments as indicated by the statistical analysis employing the split plot design. INTRODUCTION ALTHOUOH COFFEE abounds in carbohydrates and several nitrogenous compounds, the phenolic acids in particular quinic acid, caffeic acid and chlorogenic acid, are supposed to be primarily responsible for both the flavor and aroma of coffee. (1.~ Chlorogenic acid is one of the esters of quinic acid and upon hydrolysis yields caffeic acid. ~s) Chlorogenic acid exists in the leaves and seeds of coffee associated with * This paper was prepared in connection with work under contract No. AT-(40-1)-1833 with the U.S. Atomic Energy Commission. The Commission retains a non-exclusive, royalty-free license in and to any copyright covering this paper, with the right to authorize others to reproduce all or any part of the copyrighted paper. This paper is a part of the M.S. Thesis of the second author, University of Puerto Rico, Mayaguez, Puerto Rico.
sugars and proteinacious substances. These complexes are supposed to be responsible for the organoleptic and stimulating effects of coffee besides being protective mechanisms against plant pathogens, t~-6~ Several monosaccharides and complex polysaceharides such as galactosans, glucosans, arabinogalactosans, and mannosans from coffee have also been reported in literature. ~7-9~ The occurrence of nitriles and heterocyclic compounds in coffee is well known. ~1'1°) However, there is no evidence for free amino acids in coffeetl~ and the proteins and their complexes are not well characterized as their isolation is very difficult. ~1'~ The mechanisms of the chemical changes occurring in the process of roasting of coffee are not well established but it is theorized that the pyrolysis of the carbohydrates at temperatures above 100°C results in formation of volatile compounds responsible for the aroma
656
Effects of roasting temperatures and gamma irradiation of coffee. ~9.xo~ T h e p r i m a r y effect of ionizing radiation on the polysaccharides is known to be liberation of monosaccharides or simpler sugars. I t was, therefore, decided to study the possible contribution of ionizing radiation in liberation of sugars or free a m o n o acids from radiolysis of proteins to form Maillard type condensation products, ~x2~ and in liberation of the chlorogenie and eaffeic acids which presumably cause enhancement of flavor. MATERIALS
AND METHODS
Pre~Oaration of coffee extracts Coffee seeds of two local varieties, Goffea eanephora L. var. Robusta and Coffea arabica L. vat. Borbon, were subjected to irradiation at 0.5 Mrad, 1.0 M r a d and 12 Mrad, with a 2,500 Ci source of e°Co. T h e samples were so positioned that the dose rate was approx. 800 rad/min. Unirradiated seeds were used as controls. T h e coffee beans were further weighed and roasted for 10 rain in an a l u m i n u m p a n surrounded b y a heating mantle at 200°C and 250°C, respectively, and weighed again in order to account for the loss in weight caused by formation of volatile compounds. T h e green and roasted coffee beans were ground to pass 60 mesh sieve size with a Wiley mill a n d dried to a constant weight in a v a c u u m oven at 50°C. The extraction procedure reported by Moore, s ~x was slightly modified as follows. A 500 m g sample of the pulverized coffee from each treatment was added to 2 5 0 m l of distilled water in a volumetric flask, and it was held at 80°C in a water b a t h for 20 rain. Later the volume was adjusted to 250 ml and the extract was filtered with sintered glass filters by suction. T h e first 25 mi of the filtrate was discarded and the coffee grounds were saved for further analyses.
The eolorimetric analysis of ehlorogenio acid, eaffeie acid, and the soluble carbohydrates The coloHmetric method reported by MOORES
et al. ~ was partly modified for determination of chlorogenic and caffeic adds. A 3 0 m l aliquot of the coffee extracts was treated with 0.30 g of potassium acetate and 2 ml of saturated basic lead acetate. T h e mixture was heated for 5 rain in a boiling water hath, cooled in an ice bath while the contents were
657
kept agitated for 1 hr with a magnetic stirrer, and filtered with a fluted filter paper. T h e absorbance of these filtrates was measured by means of a Beckman DB spectrophotometer, at 324 n m for chlorogenic acid a n d at 347 n m for caffeic acid. Since other constituents of roasted coffee also absorb at these wavelengths, a 5 ml aliquot of the original extract was diluted to 100 ml and the absorbance of this solution was also measured at the settings of 324 n m and 347 nm. One-tenth of the absorbance of the samples treated with lead acetate was subtraced from the absorbance of the untreated extracts. The total content of the soluble carbohydrates was determined according to the colorimetric procedure after modification of the method of MoRms ~Is~ with stabilized anthrone reagent. T h e original coffee extracts were diluted in the proportion of one to two, and one ml aliquot of this were transferred to 25 m test tubes. T h e tubes were cooled in an ice b a t h and 5 ml of the anthrone reagent was added to each tube. T h e tubes were heated for exactly I 0 min in a boiling water bath and cooled again in an ice bath. T h e absorbance of the color complex developed was measured at 600 n m on the Beckman DB spectrophotometer, and the concentration of the samples was determined by means of a standard curve.
Determination of the nitrogen content of the coffee extracts T h e nitrogen content of the pulverized coffee beans was determined according to the official method o f A . O . A . C . ~14~ A 50 m g sample of the coffee powder, which was sieved with a 60 mesh screen and dried under v a c u u m to constant weight, was transferred to a 2 5 m l miero-Kjeldahl digestion flask. As a catalyst, 0.1 g of K s S O 4 and H g O mixture was added. After addition of 2 ml of concentrated HsSO~, the flasks were heated on electric burners until the contents were digested to a colorless liquid. These were further subjeeted to distillation and titration. All the treatments were replicated three times, and all the analyses for each treatment in turn were m a d e in triplicate. T h e data were subjected to analysis of variance using the split-split plot design. ~15)
658
S. N. Deshpande and A. A. Aguilar TABLE 1. Percentage of chlorogenic acid in coffee C. Cane~hora Dose (Me~arad)
0
O. 5
i0.2 i0.7 11.4
2~ °
--
C. Arabica 1
12
0
O. 5
1
12
ii. 2 ii. 4 11.5
i0.8 ii. 6 11.7
ii. 5 ll. 4 10.9
7.4 8.5 8.4
8.2 8.1 8.9
7.9 7.7 8.6
8.1 8.1 8.5
8.8
8.6
8.4
8.6
8.8
8.7
7.6
9.1
8.4
6.1 6.0 6.1
5.4 5.9 5.1
5.8 6.2 6.1
5.8 6.1 5.3
4.9 4.9 5.0
1.4 1.6 1.5
2.2 2.4 2.2
2.4 2.0 2.4
2.2 1.3 2.l
1.4 1.8 1.4
1.9 1.8 1.9
1.6 1.8 1.8
1.7 1.8 1.9
Roasting Te~erature ('C) Unroasted Green
250__°
RESULTS AND DISCUSSION The roasting treatments seem to cause a decrease in the concentration of chlorogenic acid, compared with concentrations of green coffee (Table 1). The effect of radiation treatments is noticeable at the 12 Mrad level For irradiated samples roasted at 250°C there is a slight increase in the concentration of chlorogenic acid. The analysis of variance for the concentration of chlorogenic acid showed a significant variation for differences in the species of coffee, roasting treatments and radiation doses (Table 6). The effects of the various treatments on caffeic acid are reported in
Table 2. A slight decrease in percent concentration was observed as a result of the roasting temperatures. Caffeic acid seemed to withstand the roasting treatments. The effect of radiation treatment was not so wall defined with respect to caffeic acid. The analysis of variance, does, however, show significant differences in the concentrations of caffeic acid within species, roasting treatments, and radiation doses (Table 6). The roasting treatment manifested up to 8 0 ~ decrease in the concentration of the total carbohydrates (Table 3). This evidenced pyrolysis, and oxidation of the carbohydrates to form volatile
TABLE 2. Percentage of caffeic acid in coffee C. Canephora Dose (Megarad)
0
0.5
C. Arabica 1
12
0
0.5
1
12
Roasting Temperature (°C) Unroasted Green
22.2 23.8 24.4
25.1 24.6 24.2
23.8 25.1 24.2
21.4 21.5 23,0
19.8 23.0 22.3
21.4 23.2 22.8
22.0 23.4 22.7
21.8 21.5 23,4
200°
15.6 16.7 16.6
17.1 18.5 18.3
21.0 20.0 17.3
17.5 17.2 17.3
19,0 19.2 15.8
17,5 17.2 17.6
18.3 18.9 16.7
18.5 18.5 18.7
250°
17.0 17.5 16.6
17.7 19.0 18.3
17.5 19.0 18.0
17.1 17.0 17.1
17.0 16.5 16.6
17.3 18.5 17.7
16.4 18.5 17.5
17.6 17.8 19.0
Effeas of roasting t~mperatures and gamma irradiation
659
TmaLx 3. Percentage of total carbohydrates in coffee C. Canephora
C. Arabica
Dose
(Megarad)
0
0.5
i
12
0
0.5
1
12
9.9 10.7
lO.5 ~.5
lO.3 11.1
11.9 12.o
12.7 14.5
12.5 14.4
12.3 14.3
15.4 15.3
12.1
~.0
10.4
11.7
13.3
13;2
13.6
16.9
Roasting Te~erature (°C) Unroasted Green
200 @ IL
25o__"
4.9 5.9 6.1
5.5 5.5 5.3
4.7 5.0 4.9
5.8 6.0 5.9
5.9 5.7 5.8
5.1 5.5 5.3
5.3 5.9 5.5
5.9 5.8 5.7
2.9 2.5
4.0 3.8
4.0 4.1
3,8 4.2
2.8 2.6
3.8 4.1
3,2 3,7
3.6 3.5
2.5
4.4
4.3
compounds which were released in the process of roasting with the characteristic aroma of coffee (Table 5). Irradiation increased the concentration of the soluble sugars by cleavage of glycosidic linkages of the structural polysaccharides of coffee. T h e effect was pronounced at the radiation dose of 12 Mrad. At the higher roasting temperature of 250°C, an increase in the soluble carbohydrate content was observed at all the doses of radiation. Radiation and the high temperatures of roasting presumably caused degradation of the polysaccharides and the various polysaccharide
4.2
2.5
4.2
3.6
derivatives to simpler sugars, chlorogenic acid and caffeic acid. T h e doses of 0.5 mrad and 1.0 M r a d were not adequate for cleavage of these complex polysaccharides, in green coffee. Perhaps these changes were further accentuated in conjunction with the roasting temperatures. T h e analysis of variance for the soluble carbohydrates showed a significant variation between the species of coffee, roasting temperatures and the radiation doses (Table 6). T h e effect of the various treatments on the nitrogen content are reported in Table 4. There seemed to be no noteworthy changes influenced by
TABLE4. Percentage of nitrogen in coffee C, Arabica
C. Canephora Dose
(Me~arad)
0
0.5
1
2.3 2.9 2.7
3.0 3.2 2.9
3.1 3.2 3.2
200 °
2.8 2.5 2.9
3.0 3.1 3.1
250_ °
3.2 3.3 3.4
3.1 2.6 3.3
12
0
0.5
i
12
2.8 2.7 2.8
2.6 2.7 2.3
2.6 2.7 2.4
2.7 2.7 2.3
2.3 2.1 2.5
3.3 3.2 3.1
3.0 3.2 3.1
2.0 2.6 2.5
2.4 2.6 2.5
2.7 2.7 2.6
2.8 2.3 2.7
3.3 3.3 3.1
3.4 3.1 3.6
2.8 2.7 2.9
2.9 2.8 2.7
2.7 2.8 2.7
3.0 2.6 3.0
Roasting Temperature (°C) Unroasted Green
3.8
S. N. Deshpandeand A. A. Aguilar
660
TABLE 5. ~ moisture content and loss of weight in roasted coffee C. Canephora Dose (Megara~)
C. Arabica
0
0.5
i
12
0
0.5
i
12
10.4
15.0
12.0
11.8
11.4
12.5
11.8
10.3
2OO °
~L.2
12.9
14.6
16.~
15,0
15.5
15.4
19.0
250 °
35.8
29.6
29.3
25.0
35.6
32.8
35.0
32.7
% Humidity: Loss i~ Weight:
ionizing radiation or the roasting temperatures in the nitrogen content. The two different species of coffee seemed to manifest a distinctly different behavior with respect to the content of chlorogenic acid. Coffea arabica had inherently less content of
chlorogenic acid and it was affected most by the roasting treatments. Considering the possibility that caffeic acid can be produced by degradation of chlorogenic acid; a lesser content of caffeic acid in Coffea arabiea even after roasting treatment confirmed the fact that Coffea arabica
TABLE 6. Summary of the statistical analysis for treatments of coffee Serial Number
Compounds Analyzed
F. Values found
F. at 1% tabulated
F at 5% tabulated
Significance
For Dose of Gamma Radiation: i
Total Carbohydrates
20.2
4.4
2.8
++
2
Chlorogenic acid
11.9
4.4
2.8
÷+
3
Caffeic acid
5.1
4.4
2.8
++
1521.5
8.6
4.5
++
For Roasting Temperatures: 1
Total Carbohydrates
2
Chlorogenic acid
688.0
8.6
4.5
++
3
Caffeic acid
188.L
8.6
4.5
++
115.9
98.5
18.5
++
For Varieties of Coffee: i
Total Carbohydrates
2
Chlorogenic acid
38.2
98.5
18.5
++
3
Caffeic acid
33.9
98.5
18.5
++
$++
gigniflcan% at ~ Significant at
Effects of roasting temperatures and gamma irradiation
was affected most by the roasting treatments. T h e behavior of the two varieties cannot be differentiated on chlorogenic acid or caffeic acid with respect to the effects of ionizing radiation. Coffea arabica h a d an initially higher content of the total carbohydrates, and it was, therefore, affected more by both the radiation treatments and the roasting treatments. T a b l e 5 shows the percent loss in weight of coffee seeds after the roasting treatment. CONCLUSIONS T h e radiation dose of 12 M r a d produced simpler compounds by fragmentation of the complex polysaccharides. T h e thermal decomposition of these simpler compounds produced by radiation resulted in volatile compounds responsible for the characteristic flavor. There was no evidence for the existence or liberation of free a m o n o acids or similar nitrogenous compounds by the action of radiation. Thus the possibility of the subsequent tbrmation of the Maillard type condensation products in increased amounts under the influence of high temperatures is perhaps precluded. T h e chlorogenic acid seems to undergo thermal degradation to yield caffeic acid. T h e characteristic flavor of coffee seems to be due to the sugar esters of chlorogenie, and caffeic acids. T h e nitrogenous compounds of coffee withstand the roasting treatments almost entirely.
661
REFERENCES 1. MOORES R. G., DOROTY L. and Wood T. R. Analyt. Chom. 20, 620 (1948). 2. WOLFROM M. L., PLUNKETT R. A. and LAVER M. L. d. agr. Fd Chem. 8~ 58 (1960). 3. POmZNTAJ. V. and BURNS E. E. d. Fd Sci. 36, 490 (1971). 4. HARBORNEJ. B. and CORNERJ. J. Biochem. J. 81, 242 (1961). 5. HASLAM E., MAKmSON G. K. and N A U ~ N M. O. J. Chem. Soc., 2137 (1964). 6. SOSULSKIF. W., So~au~a~ F. S. and Brtha-rv R. S. J. Can. Inst. Fd. TechnoL 5, 101 (1972). 7. WOLFROMM. L., LAVER M. L. and PATIND. L. J. org. Chem. 26, 4533 (1961). 8. WOLVROMM. L. and PATIN D. L. J. agr. Fd Chem. 12, 376 (1964). 9. WoLm~O~ M. L. and PA~N D. L. J. org. Chem. 30, 4060 (1965). 10. MEaarr C. Jr., BAZINETM. L., SULLIVANJ. H. and ROBERTSON D. H. J. agr. Fd Chem. 11, (2), 152 (1963). 11. SMITH A. K. and JOHNSEN V. L. Cereal Chem. 25, 399 (1948). 12. HODOEJ. E. J. agr. Fd Chem. 1, 925 (1953). 13. Mogms D. L. Science 107, 254 (1948). 14. Association of Official Agricultural Chemists. Official Methods of Analysis. Association of Official Agricultural Chemists, Washington, D.C. (1960). 15. SNEDECORA. W. and C o c H ~ W. W. Statistical Methods. The Iowa State University Press, Ames (1971).