HASHIM Uso de La Methilpirazina Para Monitorear El Tostado Del Cafe

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    .SEVIER

    Food Research nternational ol. 28, No. 6, pp. 619423, 1996Copyright 0 1996 Canadian Institute of Food Science and TechnologyPublished by Elsevier ScienceLtdPrinted in Great Britain0963-9969/96 15.00 + 0.00

    0963-9969 95)00037-Z

    Use of methylpyrazine ratios to monitor thecoffee roastingL. Hashim & H. Chaveron

    Lubor at oir e Biophysicochimi e et Technologie Ali mentai res Uni versit e de Technologie de Compt igne B. P. 649 60206 Compi Pgne France

    The formation of methylpyrazines has been determined in roasted coffee beans(Arabica and Robusta). The determination of different methylpyrazines wasstudied by the coupled steam distillation-microdistillator as extraction methodand gas chromatography using a capillary column and a thermionic detector.The pyrazine; 2-methyl-; 2,3-dimethyl-; 2,5-dimethyl-; 2,6-dimethyl-; trimethyl-and tetramethyl pyrazine were detected in coffee beans. The principal compoundwas 2-methylpyrazine. The concentration of the latter pyrazine was more than2000 &lo0 g of coffee beans depending on the time, the temperature of roast-ing and the origin of the beans. The correlation of the methylpyrazine quantitywith the sensory analysis of the beans has shown the possibility of monitoringthe roasting process of coffee beans. Copyright 0 1996 Canadian Institute ofFood Science and Technology. Published by Elsevier Science Ltd.Keyw ords: coffee Arabica, Robusta, roasting, methylpyrazines, gas chromato-graphy, thermionic detector.

    INTRODUCTIONThe aroma of green coffee beans is very weak and difFi-cult to describe; roasting is an essential technological pro-cess for the development of coffee aroma. Coffee volatilesare numerous and varied in their aroma quality, potencyand concentration, and all contribute to the overallaroma. Most of the volatiles are derived from non-volatile components of the raw bean, which break downand react during roasting, forming a complex mixture.The final composition of volatiles depends on a numberof factors, including species/variety of bean, climaticand soil conditions during growth, storage of the beans,the time and temperature of roasting (Dart et al., 1985).

    Although extensive work has been conducted todetermine the volatile constituents of coffee aroma, noevidence exists to suggest that one single compound hasan immediately recognisable coffee-like aroma. Certainclasses of compound have, however, been suggested asmajor contributors to aroma, e.g. where the carbonylcompounds were removed from a coffee aroma concen-tration, a full coffee aroma was no longer present. Ithas been also reported that the phenolic compoundsmade an important contribution to the coffee aroma(Dart et al. 1985). Particular attention has been paidto pyrazines in many foods, and quantitative data indi-

    cate that some are present in coffee at levels exceedingtheir threshold value, and therefore, have a high odourvalue (Clifford, 1975).Feldman et a l 1969) reported that sugars, trigonelline,chlorogenic acid and protein may be involved in coffeearoma production. Maillard reactions and Streckerdegradations are frequently quoted and popularlyaccepted as the origins of aroma volatiles.

    Maga (1982) indicated that the examination of roast-ing-simulating model systems showed that pyrolysis ofsugars and polysaccharides gave rise to a wide rangeof volatiles including aliphatic carbonyls, alcohols andacids, furans and cyclic diketones. Simultaneous inter-action with a nitrogen-containing fragment could giverise to pyrazines, pyridines, pyrroles and, in some cases,imidazoles. Pyridines might also form from trigonelline,and pyrazines among the volatiles produced from thePhydroxy amino acids, serine and threonine.

    Many pyrazines are recognized as the volatiles con-tributing to roasted aromas of cooked foods (Shimodaet al. 1990). Maarse et al (1989) have listed more than700 components which have been isolated from coffeearoma. During the last two decades, evidence has accu-mulated that a class of heterocyclic nitrogen-containingcompounds directly contributes to coffee aroma. Themajority of the heterocyclic substances identified in

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    620 L. Hashim H . Chaveron

    coffee aroma are furans, pyrroles, thiophenes, pyridinesand pyrazines. There are 81 pyrazines already identifiedin coffee aroma, whose concentrations are variabledepending on the time and temperature of the thermaltreatment (Dart et al. 1985).The present study undertook to establish a relationshipbetween the ratio of several alkylpyrazines in differenttypes of roasted coffee (Arabica and Robusta), and thesensory analysis of coffee beans.

    METHODS AND MATERIALS

    Laboratory roasted coffee: Arabica green coffee beans,(Ivory Coast) were roasted at various temperatures (187,199,205,207 and 213C) for 10 min. Robusta green coffeebeans (Colombia) were roasted for different times (9 min30 s, 10 min 25 s, 11 min, 11 min 45 s and 13 min) at185C. The coffees were roasted with a laboratory roasterat the Research Institute of Coffee and Cocoa (Montpel-lier, France). The beans were coarsely ground to 500 eand used for the extraction of volatile components.Sensory evaluation: for this study a trained panelconsisting of 10 judges was chosen among the person-nel of the laboratory. The ability of the judges to detectdifferences between sweet, sour, salty and bitter solu-tions at various concentrations was tested. They weretrained in both flavor and ranking tests to evaluatedifferent coffee beans. The Friedman test (varianceanalysis ANOVA) was applied to evaluate the degreeof coffee beans roasting (Piggott, 1988).

    Extraction and determination of methylpyrazines:the coupled steam distillation-microdistillator (Hashim,1990) used to extract methylpyrazines from coffee isshown in Figure 1. The sample (10 g of coffee) wasplaced in flask A with 2 g of NaCl and 10 ml of dis-tilled water. In flask B, 1 ml of a mixture of pentane-diethyl ether (2 : 1 v/v was introduced. The cold finger,in which a cooling alcohol circulates (-lOC), wasintroduced into the apparatus. Flask B was heated in awater bath at 55C. In C, 1.5 ml of distilled water and1.5 ml of the same solvent mixture were added. Theextraction time was fixed to 45 min which gave the bestrecovery extraction of methylpyrazines. All analyses werecarried out in duplicate.The determination of methylpyrazines in coffee beanswas concluded by Gas Chromatography Girdel-30(Suresnes, France) using commercial standards of thedifferent pyrazines under the following conditions (afteradding the 4-ethylpyridine to the extracts as an internalstandard for quantification of the alkylpyrazines). Thecapillary column was of fused silica Chrompack (LcsUlis, France) with diameter interior of 0.32 mm andL = 50 m and phase CP wax 52 B (polyethyleneglycol).The detector was a thermionic detector (TID), with anadditional helium flow at the outlet of the column.Helium, at a pressure of 0.8 bar, was the carrier gas.

    MICRODISl-lLLATOR

    STEAM DISTILLATION

    Fig. 1 Coupled steam distillation-microdistillator.

    The oven temperature changed at a rate of 3Wminfrom 60C to 220C. The temperature of the injectorand detector was 250C.

    RESULTS AND DISCUSSION

    The desired aroma of coffee beans results from compo-sitional changes that occur in the beans during roasting.Several researchers worked on different componentsof coffee aroma to monitor the roasting or to find thecomponent responsible for certain odors. For example,Purdon et al. (1987) used caffeoylquinic acid as anindicator to investigate compositional changes duringroasting. Vitzthum et al. (1990) found the 2-methyl-isobomeol to be responsible for the earthy, musty odorof Robusta coffee. Holscher et al. (1990) indicated thatthe number of key components responsible for thesensorially perceptible coffee aroma was small.Alkylpyrazines present an important group of coffeearomas. Pyrazines are so important from an odor stand-point that numerous researchers (Maga, 1982; Gallois,1984; Fors et al. 1986) have attempted to describe theodor properties associated with many naturally occur-ring and synthesized pyrazine derivatives and measure

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    M ethy lpy razine rat ios to monit or coffee roasting 621

    Table 1. Reported odor descriptions and odor tbreshoMs foralkylpyrazines (Mage, 1982; GaUois, 1984; Fors et al., l M)Alkylpyrazine Odor description Odor threshold(ppm)In water In oilPyrazine Corn-like withbitter noteSweet odor2-Methylpyrazine BurntRoastedGrassy2,3_Dimethylpyrazine New leatherPungentGreen2,5-Dimethylpyrazine NuttyGrassy2,6_Dimethylpyrazine Etherlike withcorn noteSweetTrimethylpyrazine Nutty

    GrassyPungentTetramethylpyrazine PungentSweetFlowery

    500 -

    a868=E5 1olw-83

    66100 21 0

    2.5400 Fig. 2. Formation of methylpyrazines in roasted coffee beans(Arabica-Ivory Coast) at different temperatures for 10 min.1.8-35 2-171.5-54 8

    940010

    2738

    in Figure 2. It was observed that the concentration ofall methylpyrazines increased linearly in relation to thetemperature of roasting and reached a maximum peakconcentration when the beans were treated at 205C -only the concentration of tetramethylpyrazine increasedweakly and regularly.

    their thresholds. A detailed listing of the reported datais presented in Table 1.For the odor perception of the different alkylpyrazines,their concentrations were not considered and thus avast array of described odors could result from thesame compound (Maga, 1982). Acree (1980) has pro-posed that perhaps there are two different odor-activesizes for certain pyrazine compounds.Maga (1982) proposed that another possible explanationfor the wide range of sensory descriptions attributed tothe same pyrazine could be the fact that the com-pounds evaluated had inclusions of minute amountsof isomeric pyrazine contaminants. In addition, theproblem has been compounded due to evaluations byuntrained evaluators and the lack of a common lan-guage even among trained evaluators.Guadagni et al . (1972) compared the odor thresholdsof alkylpyrazines both in water and in oil. Theyobserved that, generally, water thresholds were 1.5-60times lower than the oil threshold values. Apparently,pyrazines were absorbed in lipid systems and as suchwere not as volatile as in aqueous systems. This couldmean, from a practical standpoint, that if pyrazineswere utilized in food systems containing significantlevels of lipid material, higher dosage levels might berequired to achieve optimum flavoring properties,Formation of methyIpyrazines in roasted coffee beans(Arabica - Ivory Coast)The formation of the various methylpyrazines inroasted coffee beans at different temperatures is shown

    187 199 205 207

    Roastina temwrahue PC)

    TV

    213

    The 2-methyl-, the 2,5-dimethyl- and the 2,6-dimethyl-pyrazine were the most abundant pyrazines among theother alkylpyrazines. For this reason, their ratio inrelation to the temperature of roasting was calculated.Figure 3 shows the ratios between 2-methyl-/2,5-dimethylpyrazine and 2-methyl-/2,6_dimethylpyrazine.In general, the ratios between these methylpyrazinesincreased with the increasing temperature of roasting.The sensory evaluation of different roasted coffee beansshowed that there was a significant difference (P < 0.05)between the different coffees. The F value (from theFriedman test) obtained was superior to the F valuestandard. The coffee beans roasted at 199C were themost liked; the degree of roasting was medium. Thecoffee beans roasted at 213C were least liked andshowed a degree of overroasting.For the coffee beans roasted at 199C the ratiobetween 2-methyl- and 2,5_dimethylpyrazine was equal to1.7 and between 2-methyl- and 2,6-methylpyrazine wasequal to 2. These values showed that the roasting degree

    0 ,180 190 250 210 220

    Roasting emperature C)Fig. 3. Ratio of methylpyrazines vs. roasting temperaturein roasted coffee beans (Arabica-Ivory Coast) at different

    temperatures for 10 min.

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    M ethy lpyr azine rat ios to monit or cofee r oasting 623

    Fig. 7. Ratio of methylpyrazines in commercial roasted coffeebeans of various origins.

    The sensory evaluation of the three coffee bean hasnot showed a preference for a single coffee. The F value(from the Friedman test) obtained was inferior to theF standard (P < 0.05). The roasting of the three coffeebeans is considered to be medium, and their aromaticquality was very similar or difficult to distinguish.

    CONCLUSIONAlkylpyrazines are generally associated with heatedfood flavours. Although they are not responsible forthe coffee beans aroma, they could be a very useful toolin monitoring the roasting process.The extraction of the different alkylpyrazines in coffeebeans is carried out by a simple and fast extractionmethod: a coupled steam distillation-microdistillator.Gas chromatography using a capillary column with athermionic detector has permitted the precise quantifi-cation of these pyrazines.The ratios between 2-methyl-/2,5_methylpyrazine and2-methyl-/2,6-methylpyrazine are of high interest incontrolling roasted coffee beans.

    REFERENCESAcree, T. E. (1980). On the odor of 2-methylpyrazine. J.

    Agr i c. Food Chem. 28 1345-9.Clifford, M. N. (1975). The composition of green and roastedcoffee beans. Process Bio chem. May, 13-20.Dart, S. K. & Nursten, H. E. (1985). Volatile components, InCoffee, Volume I Chemistr y. ed. R. J. Clarke & R. Macrae.Elsevier, London, pp. 22365.Feldman, J. R., Ryder, W. S. & Kung, J. T. (1969). Impor-tance of non-volatile compounds to the flavor of coffee.J. Agr i c. Food. Chem., 17, 733341.Fors, S. M. & Olofsson, B. K. (1986). Alkylpyrazines,volatiles formed in the Maillard reaction. II. Sensory prop-erties of five alkylpyrazines. Chemi cal Senses 11, 65-77.Gallois, A. (1984). Les pyrazines presentes dans les aliments.Sciences des Al iment s 4 145-66.Guadagni, D. G., Buttery, R. G. & Turnbaugh, J. G. (1972).Odor thresholds and similarity ratings of some potatochips components. J. Sci. Food Agr ic. 23 1435-9.Hashim, L. (1990). Evaluation de la qualite aromatique ducafe et de la masse de cacao. These d Universite de Tech-nologie de Compiegne, France.Holscher, W., Vitzthum, 0. G. & Steinhar, H. (1990).Identification and sensorial evaluation of aroma-impact-compounds in roasted Colombian coffee. Cufi Cacao TheXXXIV, 3, juil.-Sept., 205-12.Maarse, H. & Visscher, C. A. (1989). Volat i l e Compounds inFoods. TNO-CIVO Food Analysis Institute, Zeist, TheNetherlands.Maga, J. A. (1982). Pyrazines in foods: an update. CRC Cri t icalReviews n Food Science and Nut ri ti on January, 148.Piggott, J. R. (1988). Sensory Analysis of Foods. ElsevierApplied Science, London.Purdon, M. P. & McCamey, D. A. (1987). Use of a5caffeoylquinic acid/caffeine ratio to monitor the coffeeroasting process. J. Food Sci. 52 1680-3.

    Shimoda, M. & Shibamoto, T. (1990). Isolation and identi-fication of headspace volatiles from brewed coffee with anon-column GCIMS method. J. Agr ic. Food Chem. 388024.Vitzthum, 0. G., Weisemann, C., Becker, R. & Kohler, H. S.(1990). Identification of an aroma key compound inRobusta coffees. Cafe Cacao The XXXIV, 1, janv.-mars,27-36.