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Proximate composition and fatty acids profile of green and roasted defective coffee beans
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LWT 39 (2006) 235–239 www.elsevier.com/locate/lwt
Proximate composition and fatty acids profile of green and roasted defective coffee beans Leandro S. Oliveira, Adriana S. Franca, Juliana C.F. Mendonc- a, Mario C. Barros-Ju´nior Nu´cleo de Pesquisa e Desenvolvimento em Cafe´, Departamento de Engenharia Quı´mica, Universidade Federal de Minas Gerais, R. Espı´rito Santo, 35-6o andar, 30160-030, Belo Horizonte, MG, Brazil Received 27 September 2004; received in revised form 19 January 2005; accepted 31 January 2005
Abstract Defective coffee beans are responsible for the depreciation of the quality of roasted coffee consumed in Brazil. The extraction of the oil of defective beans for applications in the food and pharmaceutical sectors is being considered as an alternative use for those beans. The objective of this work was to determine the composition of the fatty acid fraction of the pressed oil and the proximate composition of crude defective beans in order to provide subsidiary information for proposals of alternative uses for these beans. The amounts of oil extracted from the defective beans were smaller than the amounts extracted from healthy mature beans. The fatty acid composition of oils from defective beans was not significantly different than that from healthy mature coffee beans. r 2005 Swiss Society of Food Science and Technology. Published by Elsevier Ltd. All rights reserved. Keywords: Defective coffee beans; Coffee oil quality
1. Introduction Defective coffee beans are always present in the coffee produced in Brazil, due to the strip-picking harvesting and processing practices adopted by the coffee producers. Currently, these defective beans comprise a figure of about 20% of the total coffee production and they are separated from the non-defective beans prior to commercialization. The separated defective beans are usually not commercialized in international markets, for they affect the quality of the beverage when roasted with non-defective beans (Franca, Oliveira, Mendonc- a, & Silva, 2005a). Since they also represent an investment in growing, harvesting and handling in the coffee production chain, coffee producers have adopted the practice of dumping the separated beans in the Brazilian internal market. The majority of the roasting industry in Brazil has been using these defective beans in Corresponding author. Tel.: +55 31 32381777; fax: +55 31 32381789. E-mail address: [email protected] (L.S. Oliveira).
blends with healthy ones, and, overall, a low-grade roasted and ground coffee is consumed within the country. In order to eliminate these defective beans from the internal market, there is a need for proposals of more attractive alternative uses for them, and to do that an assessment of the chemical composition of the defective beans is of relevance. The chemical composition of defective beans has been scarcely studied (Mazzafera, 1999; Franca et al., 2005a). Since the use of coffee oil in the food and pharmaceutical industries has been growing expressively, attention was herein focused on the extraction and chemical profiling of this oil from defective beans, in order to propose alternative usages for them. The chemical composition of the oil of healthy coffee beans has been already studied and data are available in the literature for both crude and roasted beans (Folstar, 1985; Nikolova-Damyanova, Velikova, & Gulab, 1998; Turatti, 2001). However, since immature beans are in a different stage of maturity, and brown and black beans were subjected to microbial fermentation, there is a need to study their oil fraction in order to verify any
0023-6438/$30.00 r 2005 Swiss Society of Food Science and Technology. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.lwt.2005.01.011
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alterations in their chemical compositions and further analyze the possibility of using it in the food and pharmaceutical industries. Furthermore, since screwpressing is a more feasible oil extraction process for oils directed for food applications, the proximate composition of defective coffee beans should be determined so that proposals could be formulated for the application of the solids waste generated in the pressing of the oil in the food industry. Thus, the objective of the present work was to elucidate the proximate composition of defective coffee beans and chemical composition of the fatty acid fraction of the oil of these beans, in order to provide subsidiary information for proposals regarding the use of the defective beans and their oil in the food and pharmaceutical industry. The types of defects studied in this work were immature, brown (sour) and black beans.
2. Methodology Arabica green (crude) coffee samples were obtained from Santo Antonio Estate Coffee (Minas Gerais, Brazil). These coffee samples were subjected to selection in an electronic sorter and the beans rejected by the sorting machine comprise the samples used in the present study. These samples will be herein designated as PVA mixture, which stands for ‘‘Preto, Verde e Ardido’’, the Brazilian denominations for black, immature and sour beans, respectively. Defective and nondefective beans were manually separated from the PVA mixture. Samples of randomly selected 100 beans were separated from each lot (black, sour, immature, nondefective and PVA mixture) and roasted in a convective oven at 200 1C for 1 h. All samples (with respective replicates) were roasted simultaneously in a single batch in order to assure that the roasting conditions were the same for all of them. Also, two samples of approximately 300 g were separated from the PVA mixture and the defective (sour, immature, bored) and non-defective beans were manually separated and weighted, in order to determine the mass composition of defective and nondefective beans. The nitrogen (method 979.09) and fat (method 920.97) contents of the coffee samples were determined according to standard AOAC procedures (AOAC, 1995). Protein content was calculated as nitrogen 6.25 (method 920.87). Ash content was evaluated gravimetrically, based on the weight of the sample after burning at 580 1C during 17 h (Clarke & Walker, 1975). Moisture content was determined by evaluating weight loss after oven-drying at 105 1C for 16 h (ISO, 1983). Carbohydrate content was estimated by difference: 100 gtotal grams of water, protein, lipids and ash. Approximately 240 kg of PVA mixture was ground and submitted to two subsequent cycles of pressing in a
Mazziero Press (Sa˜o Paulo, Brazil). The screw-pressed PVA oil was submitted to transesterification, according to AOAC procedures (method 996.06), in order to obtain the fatty acids methyl esthers (FAMEs). The extracted coffee oil obtained by solvent extraction (method 920.97) for each sample (black, immature, bored and non-defective beans) was also analyzed for FAMEs. CG analyses of the FAMEs were carried out on a Shimadzu CG-17 gas chromatograph equipped with a 30 m DB-Wax capillary column (0.25 mm id) and a flame ionizing detector (N2: 2 ml/min). Splitless injection (0.5 ml per injection) was used. The injector and detector temperatures were set to 250 1C and 270 1C, respectively. Oven temperature was initially set at 165 1C for 4 min and elevated to 220 1C at the rate of 4 1C/min. The usual factors that describe the quality of edible oils were determined for the screw-pressed PVA oil according to standard AOCS procedures (AOCS, 1998). The factors herein determined were unsaponifiable matter (method Ca 6a-40), saponification value (method Tl 1a-64), free fatty acids (method Ca 5a-40), total acidity (method Cd 3d-63), iodine value (Wijs) (method Tg 1-64), and refractive index (method Cc 7-25). The obtained data were submitted to analysis of variance and the means were compared by the Duncan test at 5% probability.
3. Results and discussion The mass composition of defective and non-defective beans in the PVA mixture is shown in Fig. 1. Even though this coffee was rejected by the sorting machine, it still contained non-defective beans. However, the total content of defective beans (70%) was much higher compared to low quality coffee samples (ryoish and rio) employed in other studies, for which the content of defective beans varied from 30 to 40% (Oliveira, Franca, Glo´ria, & Borges, 2005; Franca, Mendonc- a, & Oliveira, 2005b). Also, approximately 60% of the defective beans corresponded to sour beans. Non-defective 31.2% Black 3.2% Others 4.0%
Sour 40.5%
Immature 21.1%
Fig. 1. Distribution of defective beans in the coffee sample. Others ¼ broken beans, husks, twigs, stones, etc.
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The proximate composition of green and roasted coffee beans is shown in Table 1. Since total carbohydrate was determined by difference, carbohydrate values presented in Table 1 will not be discussed in the present study. Green coffee samples presented approximately 8.5% average moisture content, with the highest value for the non-defective beans sample and the lowest value for the sour beans. Moisture levels are within the range reported in the literature: 8.5–13 g/100 g (Clarke, 1985). After roasting, moisture levels decreased to an average of 1.5 g/100 g, with no differences among the samples. Protein levels for green coffee samples varied from 14.9 to 17%. These values are within the range reported in the literature: 11–16.5% (Macrae, 1985). The black beans presented the highest protein level among the samples. According to the reviewed literature, there are no evidences indicating that the protein contents of coffees of different qualities, or even of different species (arabica vs. robusta), should be significantly different (Macrae, 1985). It is noteworthy to mention that these results were based on the determination of crude nitrogen and multiplication by the factor 6.25, so they include caffeine and trigonelline nitrogen. Previous studies using the same coffee samples have shown that black beans presented approximately 30% more caffeine than the others (Franca et al., 2005a), which could account for its higher protein levels. Thus, protein levels were corrected by subtracting both caffeine and
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trigonelline nitrogen, as shown in Table 2. Even though protein levels appear to be lower for immature beans, statistical comparison of the results (Duncan test at 5% probability) indicates that there are no differences in protein levels between defective and healthy coffee beans. Crude protein levels did not vary much after roasting, with a slight increase for the immature beans and decrease for the other samples. In view of the high temperatures attained during roasting, a decrease in protein levels was expected. The small variations observed in the present study could be attributed to the formation of volatile nitrogenous components during roasting, which contribute to protein determined by Kjeldahl nitrogen. Even though differences were small, protein levels after roasting were the highest for black and immature beans and the lowest for sour and non-defective beans. The average mineral content (ash) in green coffee varied from 4.8% to 5.8%. These values are slightly higher than the ones reported in the literature for Brazilian Arabica coffee: 4.1–4.5% (Clarke & Walker, 1975). The black beans presented the highest mineral content. Ash values presented a slight decrease after roasting for the sour and non-defective samples, without significant differences among the roasted coffee samples. The values obtained for lipid contents of crude and roasted arabica coffee beans are presented in Table 1. The lipid contents were found to be significantly
Table 1 Proximate composition of coffee beans (g/100 g dry green basis) PVA mixture
Black
Immature
Sour
Non-defective
Green beans Water Protein Fat Carbohydrate Ash
8.470.1ab,x 16.070.4ab,x 9.970.1b,y 60.9 4.870.0c,x
8.770.2ab,x 17.070.6a,x 10.070.3ab,x 58.6 5.870.1a,x
8.970.2ab,x 14.970.1b,x 9.670.7b,x 61.8 4.870.1c,x
7.970.5b,x 16.370.2ab,x 9.270.6b,x 61.4 5.270.0b,x
9.170.5a,x 14.972.1b,x 10.870.3a,x 60.0 5.270.0b,x
Roasted beans Water Protein Fat Carbohydrate Ash
1.570.2a,y 14.470.2b,y 10.370.2ab,x 67.3 4.270.6a,x
1.470.2a,y 16.170.2a,x 10.270.1b,x 65.95 4.571.0a,x
1.670.1a,y 14.570.2b,x 9.070.1c,x 67.6 4.770.6a,x
1.470.0a,y 14.670.1b,y 10.370.4ab,x 66.5 4.970.0a,y
1.370.1a,y 14.070.3c,x 10.370.1a,y 67.7 4.070.0a,y
Mean values with the same letter in the same line (a,b) or in the same column (x,y) for a specific substance do not differ significantly by the Duncan test at 5% probability.
Table 2 Corrected protein levels for green and roasted coffee (g/100 g dry green basis)
Green Roasted
PVA mixture
Black
Immature
Sour
Non-defective
13.770.4a,x 12.670.2ab,y
14.070.5a,x 13.070.2a,y
12.070.2a,y 13.070.3a,x
13.370.3a,x 11.870.1c,y
12.672.4a,x 12.370.5bc,x
Mean values with the same letter in the same line (a,b) or in the same column (x,y) for a specific substance do not differ significantly by the Duncan test at 5% probability.
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different among healthy and defective beans according to the Duncan test at 5% probability. Healthy mature coffee beans presented higher oil contents than those for defective beans. Amongst the defective beans, black beans presented higher oil contents than that for immature and sour beans. There was no significant difference among the oil contents for roasted healthy and sour beans. Regarding the effect of the roasting process on the oil content, there was a slight decrease (in dry green basis) in the oil content of healthy mature beans while the others remained constant. This fact corroborates the observation that defective beans are roasted to a lesser degree than healthy mature beans for the same processing conditions (Franca et al., 2005a). The lipid contents herein determined fall within the range encountered in the literature (9–15%) (Sivetz & Desrosier, 1979; Folstar, 1985; Speer & Ko¨lling-Speer, 2001; Turatti, 2001). It is noteworthy to mention here that for all the previously published data information was lacking regarding one or more factors that affect the oil content. In all cases, the authors failed to mention either the coffee species or NY-type classification (related to the number of defects in a lot), or the basis (green or roasted, dry or wet) used for presentation of the data. Furthermore, a diversity of methodologies was employed for oil content determination in the published data. Thus, comparison of the data should be made with care. The solvent extracted coffee oils obtained for each sample (black, immature, bored, non-defective beans) and the screw-pressed coffee oil obtained from the PVA mixture were analysed for the fatty acids profile. There were no significant differences in the amounts of all fatty acids for crude and roasted healthy and defective beans, based on the Duncan test at 5% probability. Linoleic and palmitic acids were the fatty acids found in greater proportions, with averages of 44% and 34%, respectively. The oil samples were comprised of moderate quantities of oleic (9%) and estearic (7%) acids and low quantities of araquidic (3%), linolenic (1.5%), behenic (0.7%) and eicosenoic (0.3%) acids. Miristic and palmitoleic acids were present in trace amounts. The factors that are usually employed to define the quality of edible oils were determined for coffee oils obtained by screw pressing of the mixture of defective beans (PVA). These factors are represented by the parameters: saponification value, unsaponifiable matter, free fatty acids, free acidity, iodine value, and refractive index. The unsaponifiable matter was determined for both screw-pressed and solvent-extracted PVA oil in order to verify the effects of the extraction method on this quantity. The unsaponifiable matter content determined for the solvent-extracted oil was 9.2 g/100 g oil, a value significantly smaller than that for the screwpressed oil (12.8 g/100 g oil). This was somewhat expected, since the screw-pressing is not a selective
process, thus extracting with the oil other matter than exclusively the lipidic fraction. The value obtained for the pressed oil is within the range published in the literature of 9–13 g/100 g oil for crude coffee oil (Ravindranath, Yousuf Ali Khan, & Reddy, 1972; Turatti, 2001). A high free fatty acids content was encountered for the pressed coffee oil: 4.970.4 g oleic acid/100 g oil. High values for free fatty acids content can be attributed either to inadequate storage conditions of the beans or the fact that the oil was extracted by more than one pressing cycle (Rossell & Pritchard, 1991). Spiz, Jablonka, and Pereira (1989) also found high values for free fatty acids in coffee oil (1.9–6.7 g oleic acid/100 g oil). The calculated value for free acidity (9.770.8% w/w expressed as oleic acid) was also high since it is based on the value for free fatty acids. The saponification value herein determined for the crude coffee oil presented a value of 192.071.4 mg KOH/g oil that lies within the range encountered in the literature which is 180–200 mg KOH/g oil for coffee oil (Lago, 2001) and within standards established for the trading of other edible oils, such as virgin olive oil (184–196 mg KOH/g oil). The iodine value (Wijs) was determined to be 95.575.6 and also falls within the range published in the literature for coffee oil (84.6–98.5, Lago, 2001). The refractive index determined for the coffee oil in this study was 1.46870.001 and falls outside the range determined by Lago (2001), which was 1.458–1.462. This can be attributed to the facts that the crude oil used in this study presented a high value of unsaponifiable matter and also contained fine particulate matter in it that could cause a slight increase in the measured values for refractive index.
4. Conclusions The proximate composition of both defective and non-defective coffee beans was evaluated. No significant differences in protein levels were detected for defective and non-defective beans, after correction for caffeine and trigonelline nitrogen. Significant differences were observed for ash contents of the coffee samples, with the highest values found for black beans. Non-defective coffee beans presented higher lipids contents than defective ones. After roasting, protein and ash contents remained approximately constant. There was a slight decrease in the oil content of non-defective beans, while the others remained relatively constant. Also, no differences were observed in the fatty acids compositions of all samples, crude and roasted. Thus, it can be concluded that there are only slight variations in composition of defective coffee beans compared to non-defective ones. Regarding oil quality parameters, values for crude coffee oil are within standards used in the trading of other edible oils, except for unsaponifiable
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matter content and free acidity, which presented high values. However, these values should be lowered with refining of the oil. Thus, both the oil and the resulting waste solids can be deemed suitable for use in formulations in the food and pharmaceutical industries after minor processing.
Acknowledgements The authors acknowledge financial support from CNPq, CAPES (Brazilian Government agencies) and FAPEMIG (Minas Gerais State Government agency). References AOAC (Association of Official Analytical Chemists). (1995). Official methods of analysis of AOAC International (16th ed). Gaithersburg, Maryland, USA: AOAC International. AOCS (American Oil Chemists Society). (1998). Official methods and recommended practices of the AOCS (5th ed.). Champaign, IL: AOCS. Clarke, R. J. (1985). Water and mineral contents. In R. J. Clarke, & R. Macrae (Eds.), Coffee volume 1: Chemistry (pp. 42–82). London: Elsevier Applied Science. Clarke, R. J., & Walker, L. J. (1975). The interrelationships of potassium contents of green, roasted and instant coffees. In Proceedings of the 7th international scientific colloquium on coffee (pp. 159–163). Hamburg: ASIC—Association Scientifique Internationale du Cafe´. Folstar, P. (1985). Lipids. In R. J. Clarke, & R. Macrae (Eds.), Coffee volume 1: Chemistry (pp. 203–222). London: Elsevier Applied Science. Franca, A. S., Oliveira, L. S., Mendonc- a, J. C. F., & Silva, X. A. (2005a). Physical and chemical attributes of defective crude and roasted coffee beans. Food Chemistry, 90(1–2), 89–94.
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Franca, A. S., Mendonc- a, J. C. F., & Oliveira, S. D. (2005b). Composition of green and roasted coffees of different cup qualities. Lebensmittel-Wissenschaft und -Technologie in press. ISO. (1983). Green coffee—determination of loss of mass on oven drying, IS6673. Lago, R. C. A. (2001). Lipı´ dios em gra˜os de cafe´. B. CEPPA (Centro de Pesquisa e Processamento de Alimentos), 19(2), 319–341 (in portuguese). Macrae, R. (1985). Nitrogenous compounds. In R. J. Clarke, & R. Macrae (Eds.), Coffee volume 1: Chemistry (pp. 115–152). London: Elsevier Applied Science. Mazzafera, P. (1999). Chemical composition of defective coffee beans. Food Chemistry, 64, 547–554. Nikolova-Damyanova, B., Velikova, R., & Gulab, N. J. (1998). Lipid classes, fatty acid composition and triacylglycerol molecular species in crude coffee beans harvested in Brazil. Food Research International, 31, 479–486. Oliveira, S. D., Franca, A. S., Glo´ria, M. B. A., & Borges, M. L. A. (2005). The effect of roasting on the presence of bioactive amines in coffees of different qualities. Food Chemistry, 90(1–2), 287–291. Ravindranath, R., Yousuf Ali Khan, R., & Reddy, O. T. (1972). Composition and characteristics of Indian coffee bean, spent grounds and oil. Journal of Food and Agriculture Science, 23(3), 307–310. Rossell, J. B., & Pritchard, J. L. R. (Eds.). (1991). Analysis of oilseeds, fats and fatty foods. London: Elsevier Applied Science 558pp. Sivetz, M., & Desrosier, N. W. (1979). Coffee technology. Westport, Co: Avi Publishing Co. Speer, K., & Ko¨lling-Speer, I. (2001). Non-volatile compounds— lipids. In R. J. Clarke, & O. G. Vitzthum (Eds.), Coffee: Recent developments (pp. 33–49). Oxford: Blackwell Science. Spiz, R. R., Jablonka, F. H., & Pereira, D. A. (1989). Composica˜o em a´cidos graxos: Triacilglicero´is, monoe´steres de diterpenos e o´leo de gra˜os de cafe´. Congresso Brasileiro de Cieˆncia e Tecnologia de Alimentos (p. 151). Resumos, Rio de Janeiro: SBCTA (in portuguese). Turatti, J. M. (2001). Extrac- a˜o e caracterizac- a˜o de o´leo de cafe´. Simpo´sio de Pesquisa dos Cafe´s do Brasil (Vol. 2, pp. 1533–1539). Vito´ria (in portuguese).
LWT 39 (2006) 235–239 www.elsevier.com/locate/lwt
Proximate composition and fatty acids profile of green and roasted defective coffee beans Leandro S. Oliveira, Adriana S. Franca, Juliana C.F. Mendonc- a, Mario C. Barros-Ju´nior Nu´cleo de Pesquisa e Desenvolvimento em Cafe´, Departamento de Engenharia Quı´mica, Universidade Federal de Minas Gerais, R. Espı´rito Santo, 35-6o andar, 30160-030, Belo Horizonte, MG, Brazil Received 27 September 2004; received in revised form 19 January 2005; accepted 31 January 2005
Abstract Defective coffee beans are responsible for the depreciation of the quality of roasted coffee consumed in Brazil. The extraction of the oil of defective beans for applications in the food and pharmaceutical sectors is being considered as an alternative use for those beans. The objective of this work was to determine the composition of the fatty acid fraction of the pressed oil and the proximate composition of crude defective beans in order to provide subsidiary information for proposals of alternative uses for these beans. The amounts of oil extracted from the defective beans were smaller than the amounts extracted from healthy mature beans. The fatty acid composition of oils from defective beans was not significantly different than that from healthy mature coffee beans. r 2005 Swiss Society of Food Science and Technology. Published by Elsevier Ltd. All rights reserved. Keywords: Defective coffee beans; Coffee oil quality
1. Introduction Defective coffee beans are always present in the coffee produced in Brazil, due to the strip-picking harvesting and processing practices adopted by the coffee producers. Currently, these defective beans comprise a figure of about 20% of the total coffee production and they are separated from the non-defective beans prior to commercialization. The separated defective beans are usually not commercialized in international markets, for they affect the quality of the beverage when roasted with non-defective beans (Franca, Oliveira, Mendonc- a, & Silva, 2005a). Since they also represent an investment in growing, harvesting and handling in the coffee production chain, coffee producers have adopted the practice of dumping the separated beans in the Brazilian internal market. The majority of the roasting industry in Brazil has been using these defective beans in Corresponding author. Tel.: +55 31 32381777; fax: +55 31 32381789. E-mail address: [email protected] (L.S. Oliveira).
blends with healthy ones, and, overall, a low-grade roasted and ground coffee is consumed within the country. In order to eliminate these defective beans from the internal market, there is a need for proposals of more attractive alternative uses for them, and to do that an assessment of the chemical composition of the defective beans is of relevance. The chemical composition of defective beans has been scarcely studied (Mazzafera, 1999; Franca et al., 2005a). Since the use of coffee oil in the food and pharmaceutical industries has been growing expressively, attention was herein focused on the extraction and chemical profiling of this oil from defective beans, in order to propose alternative usages for them. The chemical composition of the oil of healthy coffee beans has been already studied and data are available in the literature for both crude and roasted beans (Folstar, 1985; Nikolova-Damyanova, Velikova, & Gulab, 1998; Turatti, 2001). However, since immature beans are in a different stage of maturity, and brown and black beans were subjected to microbial fermentation, there is a need to study their oil fraction in order to verify any
0023-6438/$30.00 r 2005 Swiss Society of Food Science and Technology. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.lwt.2005.01.011
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alterations in their chemical compositions and further analyze the possibility of using it in the food and pharmaceutical industries. Furthermore, since screwpressing is a more feasible oil extraction process for oils directed for food applications, the proximate composition of defective coffee beans should be determined so that proposals could be formulated for the application of the solids waste generated in the pressing of the oil in the food industry. Thus, the objective of the present work was to elucidate the proximate composition of defective coffee beans and chemical composition of the fatty acid fraction of the oil of these beans, in order to provide subsidiary information for proposals regarding the use of the defective beans and their oil in the food and pharmaceutical industry. The types of defects studied in this work were immature, brown (sour) and black beans.
2. Methodology Arabica green (crude) coffee samples were obtained from Santo Antonio Estate Coffee (Minas Gerais, Brazil). These coffee samples were subjected to selection in an electronic sorter and the beans rejected by the sorting machine comprise the samples used in the present study. These samples will be herein designated as PVA mixture, which stands for ‘‘Preto, Verde e Ardido’’, the Brazilian denominations for black, immature and sour beans, respectively. Defective and nondefective beans were manually separated from the PVA mixture. Samples of randomly selected 100 beans were separated from each lot (black, sour, immature, nondefective and PVA mixture) and roasted in a convective oven at 200 1C for 1 h. All samples (with respective replicates) were roasted simultaneously in a single batch in order to assure that the roasting conditions were the same for all of them. Also, two samples of approximately 300 g were separated from the PVA mixture and the defective (sour, immature, bored) and non-defective beans were manually separated and weighted, in order to determine the mass composition of defective and nondefective beans. The nitrogen (method 979.09) and fat (method 920.97) contents of the coffee samples were determined according to standard AOAC procedures (AOAC, 1995). Protein content was calculated as nitrogen 6.25 (method 920.87). Ash content was evaluated gravimetrically, based on the weight of the sample after burning at 580 1C during 17 h (Clarke & Walker, 1975). Moisture content was determined by evaluating weight loss after oven-drying at 105 1C for 16 h (ISO, 1983). Carbohydrate content was estimated by difference: 100 gtotal grams of water, protein, lipids and ash. Approximately 240 kg of PVA mixture was ground and submitted to two subsequent cycles of pressing in a
Mazziero Press (Sa˜o Paulo, Brazil). The screw-pressed PVA oil was submitted to transesterification, according to AOAC procedures (method 996.06), in order to obtain the fatty acids methyl esthers (FAMEs). The extracted coffee oil obtained by solvent extraction (method 920.97) for each sample (black, immature, bored and non-defective beans) was also analyzed for FAMEs. CG analyses of the FAMEs were carried out on a Shimadzu CG-17 gas chromatograph equipped with a 30 m DB-Wax capillary column (0.25 mm id) and a flame ionizing detector (N2: 2 ml/min). Splitless injection (0.5 ml per injection) was used. The injector and detector temperatures were set to 250 1C and 270 1C, respectively. Oven temperature was initially set at 165 1C for 4 min and elevated to 220 1C at the rate of 4 1C/min. The usual factors that describe the quality of edible oils were determined for the screw-pressed PVA oil according to standard AOCS procedures (AOCS, 1998). The factors herein determined were unsaponifiable matter (method Ca 6a-40), saponification value (method Tl 1a-64), free fatty acids (method Ca 5a-40), total acidity (method Cd 3d-63), iodine value (Wijs) (method Tg 1-64), and refractive index (method Cc 7-25). The obtained data were submitted to analysis of variance and the means were compared by the Duncan test at 5% probability.
3. Results and discussion The mass composition of defective and non-defective beans in the PVA mixture is shown in Fig. 1. Even though this coffee was rejected by the sorting machine, it still contained non-defective beans. However, the total content of defective beans (70%) was much higher compared to low quality coffee samples (ryoish and rio) employed in other studies, for which the content of defective beans varied from 30 to 40% (Oliveira, Franca, Glo´ria, & Borges, 2005; Franca, Mendonc- a, & Oliveira, 2005b). Also, approximately 60% of the defective beans corresponded to sour beans. Non-defective 31.2% Black 3.2% Others 4.0%
Sour 40.5%
Immature 21.1%
Fig. 1. Distribution of defective beans in the coffee sample. Others ¼ broken beans, husks, twigs, stones, etc.
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The proximate composition of green and roasted coffee beans is shown in Table 1. Since total carbohydrate was determined by difference, carbohydrate values presented in Table 1 will not be discussed in the present study. Green coffee samples presented approximately 8.5% average moisture content, with the highest value for the non-defective beans sample and the lowest value for the sour beans. Moisture levels are within the range reported in the literature: 8.5–13 g/100 g (Clarke, 1985). After roasting, moisture levels decreased to an average of 1.5 g/100 g, with no differences among the samples. Protein levels for green coffee samples varied from 14.9 to 17%. These values are within the range reported in the literature: 11–16.5% (Macrae, 1985). The black beans presented the highest protein level among the samples. According to the reviewed literature, there are no evidences indicating that the protein contents of coffees of different qualities, or even of different species (arabica vs. robusta), should be significantly different (Macrae, 1985). It is noteworthy to mention that these results were based on the determination of crude nitrogen and multiplication by the factor 6.25, so they include caffeine and trigonelline nitrogen. Previous studies using the same coffee samples have shown that black beans presented approximately 30% more caffeine than the others (Franca et al., 2005a), which could account for its higher protein levels. Thus, protein levels were corrected by subtracting both caffeine and
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trigonelline nitrogen, as shown in Table 2. Even though protein levels appear to be lower for immature beans, statistical comparison of the results (Duncan test at 5% probability) indicates that there are no differences in protein levels between defective and healthy coffee beans. Crude protein levels did not vary much after roasting, with a slight increase for the immature beans and decrease for the other samples. In view of the high temperatures attained during roasting, a decrease in protein levels was expected. The small variations observed in the present study could be attributed to the formation of volatile nitrogenous components during roasting, which contribute to protein determined by Kjeldahl nitrogen. Even though differences were small, protein levels after roasting were the highest for black and immature beans and the lowest for sour and non-defective beans. The average mineral content (ash) in green coffee varied from 4.8% to 5.8%. These values are slightly higher than the ones reported in the literature for Brazilian Arabica coffee: 4.1–4.5% (Clarke & Walker, 1975). The black beans presented the highest mineral content. Ash values presented a slight decrease after roasting for the sour and non-defective samples, without significant differences among the roasted coffee samples. The values obtained for lipid contents of crude and roasted arabica coffee beans are presented in Table 1. The lipid contents were found to be significantly
Table 1 Proximate composition of coffee beans (g/100 g dry green basis) PVA mixture
Black
Immature
Sour
Non-defective
Green beans Water Protein Fat Carbohydrate Ash
8.470.1ab,x 16.070.4ab,x 9.970.1b,y 60.9 4.870.0c,x
8.770.2ab,x 17.070.6a,x 10.070.3ab,x 58.6 5.870.1a,x
8.970.2ab,x 14.970.1b,x 9.670.7b,x 61.8 4.870.1c,x
7.970.5b,x 16.370.2ab,x 9.270.6b,x 61.4 5.270.0b,x
9.170.5a,x 14.972.1b,x 10.870.3a,x 60.0 5.270.0b,x
Roasted beans Water Protein Fat Carbohydrate Ash
1.570.2a,y 14.470.2b,y 10.370.2ab,x 67.3 4.270.6a,x
1.470.2a,y 16.170.2a,x 10.270.1b,x 65.95 4.571.0a,x
1.670.1a,y 14.570.2b,x 9.070.1c,x 67.6 4.770.6a,x
1.470.0a,y 14.670.1b,y 10.370.4ab,x 66.5 4.970.0a,y
1.370.1a,y 14.070.3c,x 10.370.1a,y 67.7 4.070.0a,y
Mean values with the same letter in the same line (a,b) or in the same column (x,y) for a specific substance do not differ significantly by the Duncan test at 5% probability.
Table 2 Corrected protein levels for green and roasted coffee (g/100 g dry green basis)
Green Roasted
PVA mixture
Black
Immature
Sour
Non-defective
13.770.4a,x 12.670.2ab,y
14.070.5a,x 13.070.2a,y
12.070.2a,y 13.070.3a,x
13.370.3a,x 11.870.1c,y
12.672.4a,x 12.370.5bc,x
Mean values with the same letter in the same line (a,b) or in the same column (x,y) for a specific substance do not differ significantly by the Duncan test at 5% probability.
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different among healthy and defective beans according to the Duncan test at 5% probability. Healthy mature coffee beans presented higher oil contents than those for defective beans. Amongst the defective beans, black beans presented higher oil contents than that for immature and sour beans. There was no significant difference among the oil contents for roasted healthy and sour beans. Regarding the effect of the roasting process on the oil content, there was a slight decrease (in dry green basis) in the oil content of healthy mature beans while the others remained constant. This fact corroborates the observation that defective beans are roasted to a lesser degree than healthy mature beans for the same processing conditions (Franca et al., 2005a). The lipid contents herein determined fall within the range encountered in the literature (9–15%) (Sivetz & Desrosier, 1979; Folstar, 1985; Speer & Ko¨lling-Speer, 2001; Turatti, 2001). It is noteworthy to mention here that for all the previously published data information was lacking regarding one or more factors that affect the oil content. In all cases, the authors failed to mention either the coffee species or NY-type classification (related to the number of defects in a lot), or the basis (green or roasted, dry or wet) used for presentation of the data. Furthermore, a diversity of methodologies was employed for oil content determination in the published data. Thus, comparison of the data should be made with care. The solvent extracted coffee oils obtained for each sample (black, immature, bored, non-defective beans) and the screw-pressed coffee oil obtained from the PVA mixture were analysed for the fatty acids profile. There were no significant differences in the amounts of all fatty acids for crude and roasted healthy and defective beans, based on the Duncan test at 5% probability. Linoleic and palmitic acids were the fatty acids found in greater proportions, with averages of 44% and 34%, respectively. The oil samples were comprised of moderate quantities of oleic (9%) and estearic (7%) acids and low quantities of araquidic (3%), linolenic (1.5%), behenic (0.7%) and eicosenoic (0.3%) acids. Miristic and palmitoleic acids were present in trace amounts. The factors that are usually employed to define the quality of edible oils were determined for coffee oils obtained by screw pressing of the mixture of defective beans (PVA). These factors are represented by the parameters: saponification value, unsaponifiable matter, free fatty acids, free acidity, iodine value, and refractive index. The unsaponifiable matter was determined for both screw-pressed and solvent-extracted PVA oil in order to verify the effects of the extraction method on this quantity. The unsaponifiable matter content determined for the solvent-extracted oil was 9.2 g/100 g oil, a value significantly smaller than that for the screwpressed oil (12.8 g/100 g oil). This was somewhat expected, since the screw-pressing is not a selective
process, thus extracting with the oil other matter than exclusively the lipidic fraction. The value obtained for the pressed oil is within the range published in the literature of 9–13 g/100 g oil for crude coffee oil (Ravindranath, Yousuf Ali Khan, & Reddy, 1972; Turatti, 2001). A high free fatty acids content was encountered for the pressed coffee oil: 4.970.4 g oleic acid/100 g oil. High values for free fatty acids content can be attributed either to inadequate storage conditions of the beans or the fact that the oil was extracted by more than one pressing cycle (Rossell & Pritchard, 1991). Spiz, Jablonka, and Pereira (1989) also found high values for free fatty acids in coffee oil (1.9–6.7 g oleic acid/100 g oil). The calculated value for free acidity (9.770.8% w/w expressed as oleic acid) was also high since it is based on the value for free fatty acids. The saponification value herein determined for the crude coffee oil presented a value of 192.071.4 mg KOH/g oil that lies within the range encountered in the literature which is 180–200 mg KOH/g oil for coffee oil (Lago, 2001) and within standards established for the trading of other edible oils, such as virgin olive oil (184–196 mg KOH/g oil). The iodine value (Wijs) was determined to be 95.575.6 and also falls within the range published in the literature for coffee oil (84.6–98.5, Lago, 2001). The refractive index determined for the coffee oil in this study was 1.46870.001 and falls outside the range determined by Lago (2001), which was 1.458–1.462. This can be attributed to the facts that the crude oil used in this study presented a high value of unsaponifiable matter and also contained fine particulate matter in it that could cause a slight increase in the measured values for refractive index.
4. Conclusions The proximate composition of both defective and non-defective coffee beans was evaluated. No significant differences in protein levels were detected for defective and non-defective beans, after correction for caffeine and trigonelline nitrogen. Significant differences were observed for ash contents of the coffee samples, with the highest values found for black beans. Non-defective coffee beans presented higher lipids contents than defective ones. After roasting, protein and ash contents remained approximately constant. There was a slight decrease in the oil content of non-defective beans, while the others remained relatively constant. Also, no differences were observed in the fatty acids compositions of all samples, crude and roasted. Thus, it can be concluded that there are only slight variations in composition of defective coffee beans compared to non-defective ones. Regarding oil quality parameters, values for crude coffee oil are within standards used in the trading of other edible oils, except for unsaponifiable
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matter content and free acidity, which presented high values. However, these values should be lowered with refining of the oil. Thus, both the oil and the resulting waste solids can be deemed suitable for use in formulations in the food and pharmaceutical industries after minor processing.
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