AACCTTAA UUNNIIVVEERRSSIITTAATTIISS CCIIBBIINNIIEENNSSIISS DOI 10.2478/aucft-2014-0011 SSeerriieess E E: :F Foooodd t teecchhnnoolologgyy
EFFECT OF ROASTING CONDITIONS ON CONCENTRATION IN ELEMENTS OF VIETNAM ROBUSTA COFFEE
Tran VAN CUONG*,**, Liu HONG LING*,***, Guo KANG QUAN*1, Shang JIN*, Song SHU JIE****, Tran LE LINH*****, Tran DUC TIEP**
* College of Mechanical and Electronic Engineering, Northwest A&F University, Yangling 712100, China, ** VietNam Russian Vocation College N01, Phuc Yen city 283 400, Vinh Phuc province, Viet Nam, *** Department of Wood Science and Engineering, Oregon State University, Corvallis, Oregon 97331, USA **** College of Food Science and Engineering, Northwest A&F University, Yangling 712100, China ***** Vietnam Forsetry University, Xuan Mai area, Chuong My district, HaNoi city 100000, Viet Nam
Abstract: Vietnam Robusta Coffee was roasted at different roasting degree and roasting temperature and 9 element concentrations (K, Mg, Ca, Na, Fe, Cu, Mn, Zn and Pb) of roasted coffee were analyzed by Flame atomic absorption method (FAAS) in this study. The results showed that the concentrations were ranged in 1447.97 ~ 1342.10 (mg/100g), 768.22 ~ 1259.44 (µg/g),10.35 ~ 13.15 (µg/g), and 17.38 ~ 20.97 (µg/g) for element of K, Ca, Cu and Mn in green and roasted coffee beans, respectively. All determined elements were the smallest value in green coffee, then increased with increasing roasting level and reached the highest value in Spain roast (roasting temperature of 250C). Mg concentration ranged in 682.70 ~ 3647.73 (µg/g); Fe concentration ranged in 37.20 ~ 53.44 (µg/g); Zn concentration ranged in 5.97 ~ 6.89 (µg/g) and Pb concentration ranged in 2.18 ~ 15.04 (µg/100g). Concentrations of all determined elements didn’t change with the increased roasting process.
Keywords: FAAS, Coffee bean, Green coffee bean, Roasted coffee bean, degree roasted coffee
1 Corresponding author. Mailing address: College of Mechanical and Electronic Engineering, Northwest A&F University, Yangling 712100, China. Tel : + 86 15929317953. E-mail: [email protected] Acta Universitatis Cibiniensis Series E: FOOD TECHNOLOGY 19 Vol. XVIII (2014), no. 2
INTRODUCTION
Coffee is one of the most popular drinks as well as one of the third most popular and consumed beverages around the world; besides that, it is an important economic crop in tropical developing countries (Hiroyuki et al., 2011; Qi Hun Ming et al. 2012; Mussatto et al., 2012). Coffee beans are produced worldwide, mainly in Africa, Southeast Asia and Central and South America (Hiroyuki et al., 2011). It represents an important financial source for developing countries, involving a large number of workers in the coffee production chain. Coffee quality is closely related to its processing (Van Dam et al., 2002; Riksen et al., 2009). Normally, processing procedure of coffee starts from green coffee beans submitted to a heat treatment, leading to roasted coffee beans. The ingredients of green coffee beans depend on several factors such as cultivated varieties, places of origin, cultivating methods, climate and soil conditions. Nevertheless, the chemical composition of roasted coffee beans plays a vital role in defining the quality of this beverage (Debastiani et al., 2014). Roasting is a complex process from chemical point of view, since hundreds of chemical reactions take place simultaneously, such as Maillard and Strecker reactions, degradation of proteins, polysaccharides, trigonelline and chlorogenic acids (De Maria et al., 1996). Coffee beans undergo some physical changes and several chemical reactions during roasting process, which transform, produce and degrade several substances (Leizmann et al., 2002), which are responsible for the flavor and aroma of coffee (Wei et al., 2011). Some aroma precursors, such as sucrose and trigonelline, give rise to appreciate flavour products, including furans, pyrazine, alkyl-pyridines and pyrroles (De Maria et al., 1996). The characteristic flavor and aroma of coffee result from a combination of hundreds of chemical compounds produced by the reactions that occur during roasting. Sugars and trigonelline will act as aroma precursors, originating several substances, which will affect both the flavor and aroma of the beverage. Thermal degradation of chlorogenic acids will result on phenolic substances that contribute to bitterness. A major contributor to the antioxidant activity was identified as N- Methylpyridinium, which was recently discovered alkaloid that is present in roasted coffee at concentrations of up to 0.25% on a dry weight basis (Stadler, 2002). Coffee is frequently recommended as a stimulant to prevent hypertension. Furthermore, it is a bronchodilator and a good source of potassium in the diet. Studies also showed that the association of the daily moderate consumption of coffee with lower prevalence of cirrhosis, lower risk of diabetes type 2, decreased prevalence of some types of cancer (Leizmann et al. 2002; Tavani
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et al. 2000) Coffee inhibit fat absorption and activates lipid metabolism in the liver (Higdon & Frei 2006). It decreases the risk of Parkinson’s disease (Ascherio et al., 2001), Liver cirrhosis and type 2 diabetes (Tverdal & Skurtveit, 2003). Several epidemiological studies showed that coffee associated intakes have beneficial effects on the central nervous system (CNS). Coffee consumption has been positively associated with alertness, humour, lower risk of suicides, disease, prevention of depression, and decrease of alcohol consumption and cigarette smoking (Dórea & Da Costa, 2005; Higdon & Frei, 2006). The elemental ingredients of ground coffee has been widely investigated using a variety of techniques such as inductively coupled plasma atomic emission spectroscopy (Dos Santos et al., 2010), flame atomic absorption spectroscopy (Ashu and Chandravanshi, 2011; Grembecka et al., 2007) and neutron activation analysis (Fernandes et al., 2002). One of the drawbacks of these methods is that the sample preparation is complex. This problem can be overcome by techniques such as particle-induced X-ray emission which deals mainly with solid samples. Micro-PIXE has confirmed to be an effective technique to detect the distribution of important minerals present in all kinds of beans (Cvitanich et al., 2011). Research showed that the type and concentration of chemical elements present in beverages (Such as P, Cl, K, Ca, Fe and Zn) may have significant impact on performance of the final beverage (Giulian et al., 2009). In this study, the weight loss of coffee beans at different roasting conditions was studied, and concentrations of 9 elements in green coffee and roasted Vietnam Robusta coffee were analysis.
MATERIALS AND METHODS
Samples: Coffee beans used for the experiment were purchased from Robusta coffee commercial market in Ban Me Thuat city, Dak Lak province of Vietnam. Coffee beans were dried, peeled and polished and made the humidity of them reached 12%. Defective coffee beans were handpicked and abandoned. Equipments used for experiments: Chamber electric furnace SX2-4-10, dimensions of 300*200*120 mm (length* width *height), operating voltage was 220V, rated power was 4KW, rated temperature was 1000℃ and ultimate temperature was 1050℃. Thermo Scientific ICE3500 Atomic Absorption Spectrometer, high performance, dual atomizer, double beam AA Spectrometer (American) was used to determine Ca, Mg, Fe, Cu, Mn, Zn, K , Pb and Na by Flame atomic absorption method (Dong, 2003; Filho et al., 2007). Chemicals and Reagents: Ultrapure water (resistivity 18.2 MΩcm). All inorganic acids and reagents used in the sample digestion were of analytical
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grade (HNO3 65% v/v; H2SO4 98% v/v; and H2O2 30% m/m) and were purchased from national testing center of nonferrous metals and electronic materials analysis, China. All Inorganic element standards (Ca, Mg, Fe, Cu, Mn, Zn, K, Pb and Na) were purchased from national testing center of nonferrous metals and electronic materials analysis, China. Roasting of coffee beans: Randomly selected coffee beans were put into a pan, spread on a layer and then oven roasted according to the specified processing conditions. Degrees of roasting were established according to percent difference of sample weight before and after roasting and visual inspection of the external color of the beans, since they are the most common methods adopted by coffee roasting industry. The pan was placed in the same position in the oven each time to make sure minimum difference of roasting conditions. After roasting, electric fan was cooled immediately. Grinding and storage: Roasted coffee beans were stored in sealed containers at ambient temperature for a maximum period of 24 h, grounded with an electric coffee grinder (Multi-purpose disintegrator MJ-04) at 3.5 screen size (0.30 mm) and refrigerated in sealed plastic bags prior to analysis. Measurements: Hydrochloric acid (HCl), nitric acid (HNO3) and strontium nitrate were analytically pure for high purity water, acetylene was for high purity. The multi-element reference solutions were prepared daily from 1000 mg L-1 stock solutions of each element. A working standard solution containing 50 mg L-1 Al, Cu, Fe, Mn, Zn, K, Mg, Ca and 10 mg L-1 Pb and -1 and 100 mg L K were prepared in 1% v/v HNO3 by appropriate dilution of the stock solution. Analytical curves were prepared using the standard calibration technique. A mass of coffee samples was added to the polycarbonate container until approximately half of its total volume with the magnetic bar, which tightly closed, was adapted to the support and immersed in liquid nitrogen. Samples were pulverized by the impact between coffee beans and the magnetic bar submitted to an oscillating magnetic field of 20 impacts s-1, the cryogenic mill program consisted: 8 min of pre-cool and 5 min of mill. Masses of coffee samples 400 mg of sample and 10 mg of V2O5 catalyst were transferred to glass digester tubes, followed by 3 mL of o concentrated HNO3 plus 2 ml of 30% m/mH2O2. Tubes were heated at 180 C for 2h. The final digests were transferred to 25 ml volumetric flasks and the volumes were completed with deionized water. These solutions were directly used for Cu, Fe, Mn, Zn, Pb and Na determination. For Ca, a dilution factor of 10 was necessary. For K and Mg, the solutions were diluted a hundred times. It is a good practice to filter some sample digests to avoid clogging of the nebulizer of the flame atomic absorption spectrometer. The methods of this studies analysised concentrations of elemental in coffee were used Flame atomic absorption of method, we refer to some previous studies (Dong, 2003; Filho et al., 2007).
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RESULTS AND DISCUSSION
Elemental concentration in green coffee The concentrations of different elements (Fe, Mg, Na, Mn, Cu, Zn, Ca, K, Pb) in green coffee beans were showed in Table 1. The level of K elemental appears to be highest value was 14479.70 µg/g, followed by Ca and Mg with concentrations of 768.22 and 682.70 µg/g. The element with smallest concentrations in green coffee is Pb element, which worth was 0.0218 µg/g.
Table 1. Elemental concentrations in green coffee Elemental concentrations in green coffee (µg/g) Value Fe Mg Na Mn Cu Zn Ca K Pb Maximum 44.47 719.23 85.34 9.96 18.05 6.23 793.23 15092.21 0.0245 Minimum 40.72 635.21 78.92 18.05 16.69 5.71 741.51 13836.98 0.0189 Mean 42.98 682.70 81.94 10.35 17.38 5.97 768.22 14479.70 0.0218 CV% 4.6 6.3 3.9 3.6 3.9 4.4 3.4 4.3 12.7
Analysis of elements concentration in green coffee have been many studies for the category of coffee, origin of coffee reported. The results of this study concerned with K and Cu were similar to Debastiani et al. (2014). Debastiani et al. also reported that other elements have higher concentrations than K and Cu, the highest value of Ca, it was 3366 µg/g, and it similarly changes the others like the above. Our results also conform to Filho et al. (2007). They reported that the concentrations of elements (Ca, Fe, Mn, Na and Zn) in green coffee and there was a concentrations of element Cu result was a little lower, while the K value was slightly higher. Martin et al. (1998) reported that the concentrations of elemental in green coffee including Cu, Fe, K, Mn and Zn were in accordance with our results, which lower of the elements were Na, Mg and Ca, while slightly higher value than with our reported. Krivan et al. (1993) reported that the concentrations of elements in green coffee including Ca, Cu, Fe, K, and Zn of value were similar to our results, while the concentrations of Mg were higher, and concentrations of Mg and Na were lower than our result. Tagliaferro et al. (2006) reported that the concentrations of elements including Fe, K, Zn and Cu in green coffee were similar to our results, while the Ca, Mn, Mg value were higher and the Na value were lower than our report. Dos Santos et al. (2008) reported that only the Zn value was similar to our results, while the Fe, Mn, Ca, Mg were higher, and the Cu value was lower than our report. Bertrand et al. 2008 reported that elements include Cu, Fe and K value were consistent to our results, and the rest of the other concentrations of elements were higher concentrations to our results, Oleszczuk et al. (2007) reported elements concentrations were different from our results. Previous studies have
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analyzed contents of chemical elements in green coffee with different methods. In addition, the different types of coffee and coffee origins were used, so the results of elements concentrations have differences.
Influence of roasting condition on elemental concentration of coffee Results of weight loss during roasting at 250℃ when roasting time was 8, 12, 14, 18 and 20 min, the external color of the beans changed from green to beige, brown, dark brown, dark, ultimately very dark, and mass loss values per roasting degree were 7.05 %, 12.34 %, 15.7 %, 21.8 %, 24.27 %, corresponding to American roast, Vienna roast, French roast, Italian roast and Spanish roast, respectively. It was noticed that weight loss increased with the roasting time because drying causes weight loss due to removal of water, while during the roasting stage it is mostly caused by removal of water and volatile substances, with the roasting time increasing the roasting process turned into roasting stage from drying stage, so loss rate of weight occurred faster during the last 10min. After drying stage, a significant increase of weight loss occurred due to intensive release of organic compounds, carbon dioxide and water resultant from pyrolysis and other roasting reactions (Dutra et al., 2001; Oliveira et al., 2005, Adriana S. Franca et al., 2009). Weight loss was measured to establish roasting degree correspondence between various roasting temperatures because such measurement has been proved to be a more reliable method than color inspection alone. Results of weight loss during different roasting temperature for 20, from the top to down, the roast temperature is 210, 220, 230, 240 and 250℃, the weight loss were 8.54, 11, 12.74, 18.12 and 24.27 %, respectively. It is noticed that coffee was coasted faster at higher temperature. It is noteworthy to mention that roasting temperature had a significant effect on weight loss. At lower temperature, weight loss presented a slower rate. The concentrations of nine elements in Viet Nam Robusta green and different degree of roasting coffee from the American roasted to Spain roasted coffee, results with concentration of the macroelements are shown in Figure 1, and concentrations of the microelements are showed in Figure 3. Meanwhile, elementals concentrations were analyzed in green beans and different temperature of roasting (with roasted times was 20 min) from 210℃ to 250℃, and the results with concentrations of the macroelements are shown in Figure 2, and concentration of the microelements are shown in Figure 4. Concentrations of Mg in green coffee and different degree of roasting coffee from the American roasted to Spain roasted coffee ranged from 682.70 to 3336.67µg/g, the value was lowest in the green beans and then gradually increased to reach the highest value at Italian Roast and then mitigation value at Spanish Roast shown in Figure 1. Similarly, the value of Mg
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concentrations in coffee with different roasting temperature ranged from 682.70 to 3647.73µg/g. The lowest value in green coffee, then gradually increased and reached the highest value at 220C, then dropped to 2801.44µg/g at 240C, then the value increased at 3094.47 in 250C shown in Figure 2. The concentration of Mg in roasted coffee accorded with our result (Debastiani et al., 2014; Anderson and Smith, 2002; Anthemidis and Pliatsika, 2005; Santos et al., 2008; Martin et al.,1999; Filho et al., 2007; Grembecka et al., 2007; Ashu and Chandravanshi, 2011) and have only one studies were lower values than ours (Vega-Carrillo et al., 2002). The value of K concentrations ranged from 1447.97 to 2121.82mg/100g, the concentration increased gradually from green coffee allow increasing degree of roast, and reached the highest value in Vienna roast, then decreased gradually and reached the lowest value in roasted Spanish roast, as showed in Figure 1. The change in temperature of roast gave a range of K concentrations from 1447.97 to 1667.82mg/100g, the highest value in 220C, and the lowest value in 250C, as showed in Figure 2. The potassium concentrations in roasted coffee are consistent with other reports (Debastiani et al., 2014; Vega-Carrillo et al., 2002; Anderson and Smith, 2002; Santos et al., 2008). Filho et al. (2007) Ashu and Chandravanshi (2011) reported value higher than ours, whereas three other studies showed lower values than ours (Martin et al., 1999; Tagliaferro et al., 2007; Grembecka et al., 2007).
Figure 1. Concentration of the macroelements in green coffee and different and different degree of roasting coffee
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The concentration of Ca element in green and different roasting degree and roasting temperature ranged from 768.22 to 1259.44 µg/g. The concentration of Ca element changed over with process roasted very clear, the lowest value in green coffee 768.22µg/g then increased with the level of roasting degree and roasting temperatures, reaching the highest value in Spanish roasted and 250C with value was 1259.44µg/g showed in Figure 1 and Figure 2. Some recent research’s results of the Ca concentrations in roasted coffee were similar with us (Anderson and Smith, 2002; Anthemidis and Pliatsika, 2005; Martin et al., 1999; Tagliaferro et al., 2007; Filho et al., 2007; Grembecka et al., 2007; Ashu and Chandravanshi, 2011), reported the value higher than ours (Debastiani et al., 2014; Vega-Carrillo et al., 2002; Santos et al., 2008). Meanwhile, the concentration of Na in green and roasted coffee with different roasting degree and roasting temperature ranged from 80.02 to 98.03µg/g, concentration of Na changed value in the roasting small, the lowest value in the roasted degree at Vienna roast with value was 80.02µg/g, and the highest in Spanish roast with value was 98.03µg/g showed in Figure 1. In changing of the temperature roasting, the smallest value at 220C was 74.13µg/g and highest at 250C. Na concentration levels vary with temperature roasting and degree of roasting coffee wasn't stabilize shown in Figure 2.
Figure 2. Concentration of the macroelements in green coffee at different roasting temperature
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According to Filho et al. (2007) reported the Na concentration in roasted coffee, while But these results were not in accordance with Anderson and Smith (2002), because of the change Na levels too large on the roasting process of coffee. While some recent studies reported the Na concentrations in roasted coffee were higher value than ours report (Vega-Carrillo et al., 2002; Ashu and Chandravanshi, 2011) and lower value than us (Martin et al., 1999; Martin et al., 1999; Grembecka et al., 2007). Fe as well as Na concentrations were also no large changes in the roasting process, ranged from 42.98 to 52.94µg/g with changes of roasting degree, the value decreased gradually from green coffee to the smallest value in Vienna roast, and then increased to reach a maximum value at the French Roast, and then decreased slightly shown in Figure 1. In that different change the temperature roasting, Fe element of concentration ranged from 35.08 to 53.44µg/g, reduced slightly at 210C and then increased to the highest value at 230C, then dropped to minimum value at 240C and then increased to 42.94µg/g at 250C (Figure 2). We agree with some of studies which have reported for Fe element concentrations in roasted coffee (Santos et al.2008, Martin et al.1999, Grembecka et al. 2007, Ashu and Chandravanshi 2011), while some studies reported the Na concentration in roasted coffee were higher than our reports (Debastiani et al., 2014; Anthemidis and Pliatsika, 2005; Filho et al., 2007; Tagliaferro et al., 2007), in that Tagliaferro et al. (2007) reported Fe concentrations in roasted coffee as highest. Nonetheless some studies reported values lower values than ours (Anderson and Smith, 2002; Martin et al., 1999). With the microelements Cu and Mn are the rules changing alike: they have the lowest levels in green coffee and they increase with increased degree of roasting and roasting temperatures, reaching values greater at highest roasting degree and roasting temperature. Some recent studies reported that the Cu concentrations in roasted coffee were similar to our results (Anderson and Smith, 2002; Filho et al., 2007), while some studies reported that the Cu concentrations in roasted coffee were lower value than our results (Debastiani et al., 2014; Anthemidis and Pliatsika, 2005; Anthemidis and Pliatsika, 2005; Santos et al., 2008; Martin et al., 1999; Grembecka et al., 2007). The Cu concentrations ranged from 17.38 to 20.97µg/g, and the Mn concentrations ranged from 10.35 to 13.15 µg/g (Figure 3 and Figure 4). We agree with Martin et al.1999 reported Mn concentrations in some coffee samples, the remaining samples are higher than ours. Remaining other studies have reported higher results than us (Debastiani et al., 2014; Anderson and Smith, 2002; Vega-Carrillo et al., 2002; Anthemidis and Pliatsika, 2005; Santos et al., 2008; Filho et al., 2007; Grembecka et al., 2007; Ashu and Chandravanshi, 2011).
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The Zn concentration was changed in the range from 5.90 to 6.89 µg/g with the increased roasting degree, from green coffee to the American roast fell slightly, then increased to the highest value in the French roast, then decreased gradually, as showed in Figure 3.
Figure 3. Concentration of the microelements in green coffee and different degree of roasting coffee
For increased roasting temperature, the values ranged from 5.27 to 6.45 µg/g, a slightly decrease at 210C, then the value gradually increased and reached the highest value at 250C as showed in Figure 4. We agree with some of studies have reported (Santos et al., 2008; Filho et al., 2007). while have some studies the Zn concentrations of element in roasted coffee were lower value than our results (Debastiani et al., 2014; Anderson and Smith, 2002; Martin et al., 1999; Tagliaferro et al., 2007; Ashu and Chandravanshi, 2011), and reported value lower than ours (Vega-Carrillo et al., 2002; Grembecka et al., 2007; Anthemidis and Pliatsika, 2005). The Pb concentrations had the biggest variation during the roasting process of coffee. The Pb concentrations ranged from 2.18 to 15.04 µg/100g, the lowest value is in green coffee and the highest value is in Spain roast (250C).
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Figure 4. Concentration of the microelements in green coffee at different temperature of roasting
As the roasting degree increased, the Pb concentrations increased in the American roast, then decreased slightly in Vienna roast, and then increases allow increase of degree roasting and achieve maximum value in Spain roast. Similarly, as the roasting temperature increased, it increased at 210C with the value of 12.98 µg/100g, then reduced at 213C the value was 4.09µg/100g. And then it increased very clearly, it reached the maximum value at 250C shown in Fig 4. (Ashu and Chandravanshi 2011) (Santos et al. 2008) reported Pb concentrations of element in roasted coffee higher value than our results.
CONCLUSIONS
Vietnam Robusta Coffee was roasted at different roasting degree and different roasting temperatures by increasing degree of roasting from American roast to Spain roast, and increase the temperature of roasting from 210℃ to 250℃. During the roasting process, weight of coffee beans reduced gradually. The weight loss during the first 10–12 min was due to the slow release of water and volatile components (drying stage). The increase in weight loss rate after that time can be attributed to an intensive release of organic compounds and CO2 during pyrolysis. The onset of pyrolysis can be associated with the transition between the two slopes.
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The concentrations of 9 elements (K, Mg, Ca, Na, Fe, Cu, Mn, Zn and Pb) have been analyzed by Flame atomic absorption method (FAAS) in green coffee beans and roasted coffee beans with different roasting degree and roasting temperature. The results showed that for green coffee and roasted coffee beans the K, Mg and Ca are the elements with the highest concentration, while Zn and Pb constitute trace elements. Results of the study also showed that green and roasted coffee beans have the same elemental composition, indicating that the roasting process did not eliminate any of the elements studied in this work. Except the Fe element, the other remaining elements were the lowest value in green coffee. The concentrations of Ka, Ca, Cu and Mn elements increased with increased roasting degree and roasting temperatures, and reached the highest value in the Spain roasted (250C). Other remaining elements Mg, Na, Fe, Pb and Zn of the values concentrations didn’t change value follow increasing degree of roasting and roasting temperatures of coffee.
ACKNOWLEDGMENTS. The authors are grateful for the funding support from the State Scholarship Fund from China Scholarship Council (CSC) and the State Scholarship Fund from Vietnam Scholarship Council (VIED). Technical assistance from Zong Ling Zhang, Ya Wen Lin and Nuo Shi is appreciated.
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