Food Chemistry 124 (2011) 863–868

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Food Chemistry

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Antioxidant activity, polyphenols, caffeine and melanoidins in soluble coffee:The influence of processing conditions and raw material

J.A. Vignoli a,*, D.G. Bassoli a, M.T. Benassi b

a Companhia Iguaçu de Café Solúvel S.A., Research and Development Department, BR-369, Km 88, C.Procópio, PR, Brazilb Departamento de Ciência e Tecnologia de Alimentos, Centro de Ciências Agrárias, Universidade Estadual de Londrina, Rodovia Celso Garcia Cid, Km 6, Londrina, PR, Brazil

a r t i c l e i n f o

Article history:Received 1 December 2009Received in revised form 28 June 2010Accepted 2 July 2010

Keywords:Coffea arabicaCoffea CanephoraRoasting degreeExtraction

0308-8146/$ - see front matter � 2010 Elsevier Ltd. Adoi:10.1016/j.foodchem.2010.07.008

* Corresponding author. Tel.: +55 43 3401 1542; faE-mail address: jvignoli@iguacu.com.br (J.A. Vigno

a b s t r a c t

The production of soluble coffee starts with the selection of beans and is followed by roasting, grinding,extraction and drying. Lyophilised soluble coffees extracted by various methods from light, medium anddark-roasted arabica and robusta beans were evaluated for antioxidant activity (AA) using ABTS, Folin,DPPH and FRAP techniques. Caffeine, chlorogenic acid (5-CQA) and melanoidin content was also quantified.The data were analysed by principal component analysis. The AA values derived from the various methodsused were correlated. Roasting resulted in the degradation of 5-CQA and formation of melanoidins, while AAwas largely unaffected by roasting. The extraction of soluble coffee more prominently affected the AA oflight-roasted coffee, mainly because it favoured the extraction of 5-CQA. The larger caffeine content inrobusta coffee resulted in greater AA. All of soluble coffee products studied possessed antioxidant potential,which was conferred by their concentrations of phenolic compounds, caffeine and melanoidins.

� 2010 Elsevier Ltd. All rights reserved.

1. Introduction

Coffee is a major commodity in the world economy, second onlyto petroleum (Borreli, Visconti, Mennella, Anese, & Fogliano, 2002).The most widely cultivated species are Coffea arabica (arabica) andCoffea canephora (robusta). Despite the poorer sensory quality of C.canephora, it has the advantage of allowing extraction of largeamounts of soluble solids, which enables its use in blends and inthe soluble coffee industry. Beverages prepared from roasted beanshave pleasant flavour and aroma in addition to their physiologicaleffects. The preference for different kinds of coffee beverages isstrictly associated with social habits and country cultures. Thecompany GEA Niro (Parma, Italy), a traditional producer of processlines for instant coffee and tea, reported that soluble coffee iswidely consumed (45% in Eastern Europe, 53% in Asia/Pacific, and79% in Australia), standing out in countries where tea is a tradi-tional beverage (GEA-Group Coffee, 2010). Soluble coffee exportsare a major source of revenue in Brazil due to the higher aggregatevalue of the product (ABICS, 2008).

Recently, scientific studies have pointed out the positive effect ofcoffee on human health (Coughlin, 2006). In general, recent studiesreport little evidence of health risks and considerable evidence ofhealth benefits for healthy adults as a result of moderate coffee con-sumption (Higdon & Frei, 2006). The beverage also stands out as a die-tary source of potential antioxidants, such as caffeine (Devasagayam,

ll rights reserved.

x: +55 43 3524 2542.li).

Kamat, Monhan, & Kesavan, 1996; Shi & Dalal, 1991), chlorogenicacids (Gómez-Ruiz, Lake, & Ames, 2007; Moreira, Monteiro, Ribeiro-Alves, Donangelo, & Trugo, 2005), hydroxycinnamic acids (Gallardo,Jiménez, & Garcia-Conesa, 2006), and Maillard reaction products,such as melanoidins (Borreli et al., 2002; Delgado-Andrade, Rufián-Henares, & Morales, 2005). Thus, the antioxidant capacity of coffeeis related to the presence of both natural constituents and compoundsformed during processing. The antioxidant potential of coffee hasbeen evaluated by several methods, such as ferric reducing antioxi-dant power (FRAP), 2,20-azinobis(3-ethylbenzothiazoline-6-sul-phonic acid assay (ABTS), 2,2-diphenyl-1-picrylhydrazyl assay(DPPH) and determination of total phenolics (Borreli et al., 2002; Sán-chez-Gonzalez, Jiménez-Escrig, & Saura-Calixto, 2005).

The FRAP method measures the ferric reduction of 2,4,6-tripyr-idyl-S-triazine (TPTZ). This reaction detects compounds with redoxpotentials lower than 0.7 V (the redox potential of Fe3+-TPTZ). Assaysusing the ABTS radical, including TEAC, are based on the ability ofantioxidants to scavenge the long-lived ABTS radical; using a similarmechanism, the DPPH assay measures the reduction of the stableradical 2,2-diphenyl-1-picrylhydrazyl by monitoring the decreasein its absorbance at 515 nm. The Folin–Ciocalteau method has beenused for years to measure total phenolic compounds and is also use-ful in evaluating antioxidant activity (Benzie, 1996; Prior, Xianli, &Schaich, 2005).

As compared to other beverages, coffee stands out for its antiox-idant potential. Some authors have reported greater AA for solubleand espresso coffee than those of red wine and green tea (Pellegriniet al., 2003). AA is also affected by the green bean composition and

864 J.A. Vignoli et al. / Food Chemistry 124 (2011) 863–868

processing methods. Daglia, Papetti, Gregotti, Bertè, and Gazzani(2000) studied beverages made from different coffee beans and re-ported a greater antioxidant capacity for C. canephora than for C.arabica. Del Castillo, Ames, and Gordon (2002) observed a decreasein AA that was correlated with the degree of roasting, associatedmainly with the degradation of chlorogenic acid. In contrast, theroasting process can also contribute to the formation of melanoi-dins, which have already been reported to be responsible for AAin high molecular weight fractions isolated from roasted coffee(Daglia et al., 2000).

Most studies in literature refer to the AA of roasted coffee. De-spite the great economic importance of soluble coffee, little hasbeen reported about its antioxidant potential or the influence ofprocessing conditions. To become solubilised, coffee undergoesan extraction process. The beans are roasted, ground and subjectedto successive percolation with water at temperatures ranging from100 to 180 �C. Chemically, percolation results in the selective solu-bilisation of coffee solids. Depolymerisation and degradation mayoccur during high-temperature extraction (Leloup, 2006), and pro-cess variations may affect the product’s characteristics.

Thus, the objective of this study was to evaluate the effect of solu-ble coffee processing conditions (roasting and extraction method), aswell as the effect of raw materials (C. arabica andC. canephora species),on the antioxidant capacity of coffee as measured by different tech-niques. In addition, representative compounds of the main classesof antioxidants in soluble coffees (5-CQA, caffeine and melanoidins)were analysed allowing to explain the variations observed in AA.

2. Materials and methods

2.1. Materials and samples

Coffee samples were provided by Companhia Iguaçu de CaféSolúvel (Cornélio Procópio, Paraná State, Brazil) and were repre-sentative of different degrees of roasting, extraction conditions,and raw materials.

Arabica (A) and robusta (B) coffee beans were roasted in a pilot80-kg/h Rayar roaster for 7–10 min at 214–225 �C to obtain light(L), medium (M), and dark (D) roasted beans, corresponding tolightness values (L*) of 33, 25, and 14, respectively. Lightnesswas assessed in triplicate with a Byk Gardner GmbH colorimeter(Germany) with 45/0 geometry and CIE illuminant D65. Coffeebeans were ground to obtain adequate particle size for later pro-cessing as follows: 30% retention in a 4-mm sieve, 60% retentionin a 2-mm sieve and 10% retention in a 1-mm sieve.

The samples were extracted by two processes: conventional (1)and double-extraction systems (2). Generally, a set of extractioncolumns is filled in sequence and extracted with heated water. Inthe conventional process (1), water at 180 �C is fed into the firststage (column with older coffee) and subsequently percolated inthe following stages until it reaches newer coffee. In the last stage,the extract reaches the newly added coffee and extracts its solublesolids, preserving the aroma and flavour. During the process, theamount of soluble solids in the extract increase, while the temper-ature decreases. The fresh coffee is extracted in the last column atapproximately 100 �C to minimise thermal damage. The resultingextract is then lyophilised. In the double-extraction system (2),one batch is fed into the selected stages at mild temperature andpressure, which results in a better quality extract. A second batchis fed into the remaining stages at higher temperature and pressureto increase solubilisation. A mixture of 50% of the extracts fromeach stream was lyophilised.

Antioxidant activity was determined by directly dissolving suit-able concentrations of samples in water. All samples were pre-pared in duplicate and measurements were made in triplicate.

2.2. Chemical and equipments

5-O-Caffeoylquinic acid (5-O-CQA), caffeine and gallic acid (HPLCgrade) were purchased from Sigma–Aldrich (St. Louis, MO, USA).ABTS (2,2-azinobis-3 ethyl benzothiazoline-6-sulphonic acid) andDPPH (2,2-diphenyl-1-picrylhydrazyl) were obtained from SigmaChemical CO. (St. Louis, MO, USA). Trolox (6-hydroxy-2,5,7,8,-tetramethylchromane-2-carboxylic acid) and TPTZ (2,4,6-tri(2-pyr-idyl)-S-triazine) were obtained from Fluka/Sigma–Aldrich (Vallens-baek Strand, Nordic, Denmark). Folin–Ciocalteau, acetic acid andacetonitrile were purchased from Merck (Darmstadt, Hessen,Germany).

Melanoidins were separated by dialysis using 12–14 kDa cutoffmembranes (Spectra/Por, Irving, TX, USA).

AA measurements were taken in a UV–Vis–UV mini-1240 spec-trophotometer (Shimadzu, Kyoto, Japan) and bioactive compoundswere detected by HPLC. The HPLC apparatus consisted of a DionexLC (Idstein, Hesse, Germany) equipped with a P680 gradient pump,TCC-100 column oven, automated sample injector (model ASI-100)and photodiode array detector (model PDA-100). The system isoperated by computer using Chromeleon version 6.6 software.

2.3. Determination of antioxidant activity

2.3.1. ABTS methodology (TEAC)Antioxidant capacity was estimated in terms of radical scaveng-

ing activity using the procedure described by Sánchez-Gonzalezet al. (2005). Briefly, ABTS radical cations (ABTS+�) were producedby reacting 7 mM ABTS stock solution with 2.45 mM potassiumpersulphate and allowing the mixture to stand in the dark at roomtemperature for 12–16 h before use. The ABTS+� solution (stable for2 days) was diluted with 5 mM phosphate buffered saline (pH 7.4)to an absorbance of 0.70 ± 0.02 at 730 nm. After addition of 10 lLof sample or trolox standard to 4 mL of diluted ABTS+� solution,absorbance readings were measured after 6 min using a UV–Vis1240 Shimadzu spectrophotometer. Ethanol solutions containingknown concentrations of trolox, a water-soluble analogue of vita-min E, were used for calibration. Results were expressed g of troloxper 100 g of coffee (dry matter).

2.3.2. FRAP methodologyIn FRAP experiments, the reduction power of various coffees

was estimated according to the procedure described by Sánchez-Gonzalez et al. (2005). The FRAP reagent was prepared by mixingof 2.5 mL of a 10 mM TPTZ solution in 40 mM HCl and 2.5 mL of20 mM FeCl3�6H2O with 25 mL 0.3 mM acetate buffer pH 3.6. Thissolution was incubated at 37 �C for 30 min.

Approximately 900 lL of freshly prepared FRAP reagent,warmed at 37 �C, was mixed with 90 lL distilled water and either10 lL of test sample or standard or appropriate reagent blank tomeasure AA. After 30 min at 37 �C, readings at the absorption max-imum (595 nm) were taken. Ethanol solutions containing knowntrolox concentrations were used for calibration. Results were ex-pressed g of trolox per 100 g of coffee (dry matter).

2.3.3. DPPH methodologyThe DPPH� assay has been widely used to evaluate the ability of

several free radical scavenger molecules. DPPH� assays were per-formed according to the procedure described by Casagrande et al.(2007). Briefly, solutions of coffee were prepared to obtain 2, 3, 4,6, 10 and 15 mg/mL. One millilitre of 100 mM acetate buffer (pH5.5), 1 mL of ethanol and 0.5 mL of 250 lM ethanolic DPPH� solu-tion were mixed and 10 lL of each sample of the above preparedsolutions were added. After 10 min, absorbance was measured at517 nm. A positive control was prepared in the absence of coffeesolutions, which indicates the maximum amount of free DPPH�

J.A. Vignoli et al. / Food Chemistry 124 (2011) 863–868 865

(considered 100% of free radicals in the solution), to calculate thehydrogen-donating ability (IA%) of coffee. The blank was preparedfrom the reaction mixture without DPPH� solution (Eq. (1)). TheIC50 (the concentration of substance that provides 50% reductionof free radical concentration) was determined

IA ð%Þ ¼ 100� ðAbs sample=Abs controlÞ � 100 ð1Þ

2.3.4. Folin–Ciocalteau methodologyTotal polyphenol content was evaluated using the Folin–Ciocal-

teau reagent following a method adapted from Singleton, Orthofer,and Lamuela-Raventos (1999). The sample (0.1 mL) was dilutedwith deionised water to a volume of 7.5 mL. Then, 300 lL of0.9 mol/L. Folin–Ciocalteau (FC) reagent and 1 mL of 20% Na2CO3

solution were added and deionised water was added up to a finalvolume of 10 mL. Solutions were maintained at room temperaturefor 60 min and total polyphenol content was determined at765 nm using a UV–Vis 1240 Shimadzu spectrophotometer. Gallicacid standard solutions were used for calibration. The results wereexpressed as g equivalents of gallic acid per 100 g of coffee (drymatter).

2.4. Determination of the bioactive compounds of soluble coffee

2.4.1. Determination of 5-caffeoilquinic acid (5-CQA) and caffeineHigh performance liquid chromatography (HPLC) was used to

determine 5-CQA and caffeine content (Alves, Dias, Scholz, & Ben-assi, 2006) using a 4.6 � 250 mm, 5 lm particle Spherisorb ODS2column (Waters, EUA). Compounds were eluted with gradientscontaining 5% acetic acid (A) and acetonitrile (B) as follows: 0–5 min: 4% B; 5–10 min: 10% B; 10–30 min: 10% B; 30–40 min: 0%B; 40–50 min: 4% B at a flow rate of 0.7 mL/min. Caffeine was de-tected at 272 nm while 5-CQA was detected at 320 nm. Quantifica-tion was carried out by external standardisation using a 5-pointcalibration curve with triplicate measurements: the concentrationof 5-CQA ranged from 5 to 30 lg/mL while that of caffeine rangedfrom 10 to 50 lg/mL. The samples were dissolved in ultra purewater and passed through 0.22-lm filters directly into the chro-matographic system.

2.4.2. Determination of melanoidinsA dialysis membrane separation system with a size exclusion

limit of 12–14 kDa was used as described by Bekedam, Schols, Boe-kel, and Smit (2006), with modifications. A soluble coffee solution(20 mL) with a concentration of 45% was prepared. The solutionwas transferred to the membrane and placed in a beaker with400 mL distilled water under agitation. The water was changedevery 8 h until it was colourless. The material retained on the mem-brane was lyophilised and used to estimate the mass of the materialwith molecular weight over 12–14 kDa in relation to the initial mass.This fraction, here considered to be melanoidin, was expressed as gof melanoidins/100 g of sample.

2.5. Statistical analysis

Antioxidant activity and chemical composition results weresubjected to principal components analysis by the ‘‘multivariateexploratory techniques” and ‘‘principal components and classifica-tion analysis” procedures using the Statistica 7.0 software package(STATSOFT, São Caetano do Sul, Brazil).

3. Results and discussion

Soluble coffee beverages were assayed for their antioxidantactivity by monitoring their reaction with ABTS cation, their reduc-

ing capacity by the FRAP method and their capacity to scavengeDPPH free radicals. Total phenolic compound content (Folin–Cio-calteau) was also determined (Table 1). Coffee compounds relatedto antioxidant capacity, such as caffeine, 5-CQA and melanoidins,were also quantified (Table 2).

Principal component analysis was used to evaluate the correla-tion between antioxidant activity and the chemical composition ofthe various products. The first two components (CP1 and 2) ex-plained 87% of the total variance.

CP1 was determined by the antioxidant activity of the beverageand its caffeine content, which was stable during the thermal pro-cess (Fig. 1A). It is important to note that all methods used gavesimilar antioxidant activity results for each the samples, despitetheir differing underlying mechanisms (Table 1).

The Folin method was highly correlated with the other methodsused (Fig. 1A). This assay determines the total polyphenol contentof a substance based on a redox reaction, thus it can be consideredan evaluation of antioxidant activity (Prior et al., 2005). In a studyof the influence of coffee preparation methods on antioxidant activ-ity, Sánchez-Gonzalez et al. (2005) also observed a correlation be-tween the polyphenol content determined by the Folin methodand FRAP values. In this work, the strongest correlation was foundbetween the Folin and the DPPH methods (r = 0.88), which suggestsscavenging of this radical by phenolic compounds. It is important tonote that DPPH values are represented as IC50; smaller values of IC50

correspond to higher AA values. Furthermore, the Folin results mayalso be related to the reducing capacity of the coffee beverage, whichwas evaluated by the FRAP method (r = �0.72) and ABTS radicalscavenging (r = 0.82).

CP2 correlated the 5-CQA and melanoidin contents, compoundsthat are degraded or produced during the roasting process. A neg-ative correlation was observed between these compounds; that is,the concentration of high molecular weight compounds increasedconcurrently with a decrease in 5-CQA content. No correlationwas observed between the concentrations of 5-CQA or melanoidinsand the AA results (CP1). The AA of the light and dark-roasted sam-ples was similar (Tables 1 and 2, Fig. 1A).

Thus, PCA separated the samples by AA (CP1) and/or roasting(CP2) (Fig. 1B). The lower two quadrants show a distinct groupformed by dark samples, independent of the raw material or theextraction methods used. In the higher quadrants are the lightand medium roasting samples, with the robusta coffee on the left(larger AA) and the arabica coffee on the right.

Considering the influence of the raw material on AA, in general,C. canephora samples yielded greater AA than the C. arabica sam-ples (Table 1, Fig. 1B). Similar results, commonly attributed tothe larger CGA content of robusta coffee, were reported in otherstudies of roasted coffee (Daglia et al., 2004). Nevertheless, thisstudy shows that isomer 5-CQA was present in similar or higherconcentrations in soluble arabica coffee than in robusta coffee (Ta-ble 2). According to Leloup (2006), although green robusta beanshave a higher CGA content, around 10% versus 8% in arabica coffee,these compounds seem to be more sensitive to the roasting processin a robusta coffee matrix. Clifford (1997) reported that for a sim-ilar degree of roasting, robusta coffee undergoes a larger absoluteloss of CGA, producing volatile phenols and guaiacol. Trugo andMacrae (1984) and Dias (2005) also described a similar behaviourfor arabica and robusta coffees with different degrees of roasting.Thus, the greater antioxidant capacity of robusta coffee could beattributed to its higher caffeine content (Table 2), since it corre-lated positively with AA (Fig. 1). In a study of brewing procedureinfluence, Lopez-Galilea, De Pena, and Cid (2007) also reported asignificant correlation between caffeine content and AA results ob-tained by DPPH (r = 0.83) and redox potential (r = �0.84). Parras,Martinez-Tomé, Jiménez, and Murcia (2007) evaluated the antiox-idant activity of coffee from different origins in beverages prepared

Table 1Antioxidant activity of soluble coffee obtained from different species and processing conditions evaluated by assorted methods.*

Assays Roasting degree Arabica Robusta

Extraction 1 Extraction 2 Extraction 1 Extraction 2

ABTS (g trolox/100 g) Light 18.77 ± 1.00 23.27 ± 0.00 27.28 ± 0.25 32.29 ± 3.25Medium 21.03 ± 2.25 23.53 ± 0.75 36.05 ± 1.75 32.79 ± 0.50Dark 23.78 ± 0.25 24.78 ± 0.00 33.93 ± 1.50 27.79 ± 3.75

FRAP (g trolox/100 g) Light 19.27 ± 2.25 25.03 ± 0.00 26.28 ± 1.50 29.78 ± 0.50Medium 25.03 ± 0.50 30.79 ± 0.50 34.04 ± 0.75 34.54 ± 1.00Dark 27.78 ± 0.25 26.03 ± 0.50 35.04 ± 0.75 29.78 ± 1.75

Folin (g gallic acid/100 g) Light 12.08 ± 0.51 14.97 ± 0.17 14.97 ± 0.00 18.54 ± 0.51Medium 13.09 ± 0.17 15.14 ± 1.02 16.67 ± 0.34 17.35 ± 0.34Dark 13.44 ± 0.00 13.10 ± 0.34 15.82 ± 0.17 13.44 ± 0.34

DPPH IC50 (lg/mL) Light 24.92 ± 0.55 16.11 ± 0.26 16.35 ± 0.34 14.81 ± 0.37Medium 19.87 ± 1.38 18.80 ± 0.47 16.14 ± 0.11 14.70 ± 0.20Dark 20.51 ± 0.18 20.23 ± 1.02 16.79 ± 1.04 19.47 ± 0.35

* Average of six measurements (duplicate in three repetitions) ± standard deviation.

Table 2Contents of 5-CQA, caffeine, and melanoidins of soluble coffee obtained from different species and processes.*

Roasting degree Arabica Robusta

Extraction 1 Extraction 2 Extraction 1 Extraction 2

5-CQA (g/100 g) Light 3.53 ± 0.02 4.11 ± 0.11 2.79 ± 0.06 4.24 ± 0.05Medium 1.87 ± 0.13 2.55 ± 0.03 1.71 ± 0.04 2.26 ± 0.11Dark 0.62 ± 0.03 0.40 ± 0.03 0.21 ± 0.03 0.25 ± 0.03

Caffeine (g/100 g) Light 2.84 ± 0.00 3.44 ± 0.05 3.98 ± 0.08 5.33 ± 0.02Medium 3.07 ± 0.36 4.12 ± 0.35 5.82 ± 0.11 5.54 ± 0.14Dark 3.64 ± 0.04 3.34 ± 0.15 4.75 ± 0.11 4.88 ± 0.64

Melanoidins (g/100 g) Light 23.80 ± 0.77 20.13 ± 0.59 27.30 ± 0.51 22.89 ± 0.38Medium 18.07 ± 0.45 22.08 ± 0.04 19.66 ± 2.04 21.28 ± 1.65Dark 29.64 ± 1.59 25.42 ± 0.01 30.44 ± 1.84 26.50 ± 0.19

* Average of two measurements ± standard deviation.

FOLIN

DPPH

5-CQA

MELANOIDINS

PC 1 : 61%

-1,0

-0,5

0,0

0,5

1,0

PC 2

: 26

%

R E1 M

R E1 D

A E1 M

A E1 D

R E2 M

R E2 D

A E2 M

A E2 D

R E1 LA E1 L

R E2 LA E2 L

-4

-3

-2

-1

0

1

2

3

4

PC

2 :

26%

PC 1 : 61%

FRAPABTS

FOLIN

DPPH

5-CQA

CAFFEINE

MELANOIDINS

R E1 M

R E1 D

A E1 M

A E1 D

R E2 M

R E2 D

A E2 M

A E2 D

R E1 LA E1 L

R E2 LA E2 L

-1,0 -0,5 0,0 0,5 1,0 -4 -3 -2 -1 0 1 2 3 4

(A) (B)

Fig. 1. Principal component analysis of antioxidant activity and composition of soluble coffee: variable projection (A) and scatter plot for the samples (B). Species: (A) arabicaand (R) robusta. Extraction process: conventional (1) and double extraction (2). Roasting degree: light (L), medium (M), dark (D).

866 J.A. Vignoli et al. / Food Chemistry 124 (2011) 863–868

by different procedures (espresso, italian, and brewed) and foundhigher TEAC values for caffeinated products than in decaffeinatedproducts.

Regarding the influence of roasting on AA, it is worth notingthat there is little agreement in the literature, even for roasted cof-fee, which has been the most extensively studied. Del Castillo et al.(2002) observed greater AA in medium-roasted coffee. Duarte,Abreu, Menezes, Santos, and Gouvêa (2005) found greater AA forbeverages made from light-roasted coffee. In contrast, Nicoli,

Anese, Manzocco, and Lerici (1997) reported greater AA formedium and dark-roasted coffee beverages. No reports are avail-able on soluble coffee; however, it must be taken into account thatfor soluble coffee, after roasting, there is an additional thermalextraction treatment at high temperature.

The degree of roasting showed little influence on the AA of solublecoffees. Compounds that were affected by roasting (5-CQA andmelanoidins) are not directly related to the antioxidant potentialof the beverages. This may initially seem contradictory, given the

J.A. Vignoli et al. / Food Chemistry 124 (2011) 863–868 867

acknowledged antioxidant activity of these compounds. Moreiraet al. (2005) described a strong correlation between the chlorogenicacid content and the FRAP method, especially for caffeoylquinic iso-mers. Borreli et al. (2002) evaluated AA and the melanoidin contentof green and roasted coffee (light, medium and dark roast). The ABTSmethod yielded AA values for all fractions: low (1.0–3.0 kDa), med-ium, and high molecular weight (over 100 kDa); however, the highweight fractions that contained melanoidins and the low weightfractions rich in phenolic compounds were the most active. Dagliaet al. (2004) obtained similar results for roasted coffee, correlatingAA and hydroxyl radical scavenging capacity. The authors reportedthat high molecular weight fractions of green coffee were also eval-uated; however, they did not present AA, which demonstrates thatroasting is responsible for the formation of AA compounds.

Frequently, studies of coffee AA available in the literature areeither restricted to just one roasting degree or focused on a specificclass of compounds (CGAs, caffeine, or melanoidins). A broaderanalysis of these products as a function of roasting conditions,extraction processes, and composition profiles showed that the fi-nal AA of coffee beverages results from the balance of degradedand newly formed compounds during roasting. Increasing roastingwill degrade 5-CQA and will form high molecular weight polymers,ensuring antioxidant activity remains unaffected by roasting con-ditions. In conclusion, under the conditions presently studied,these two compounds contribute equally to AA. Furthermore, thereduction of one is balanced by the formation of the other, whichexplains the similar AA values found for light and dark-roasted cof-fees. Thus, we can conclude that AA depends more on coffee com-position than on roasting degree.

In relation to the soluble coffee extraction process, the results ofthe processes studied varied according to roasting degree (Table 2).Both the arabica- and the robusta-derived products presented high-er 5-CQA contents for light and medium-roasted coffee in the dou-ble-extraction system (2). Interestingly, this process also favouredthe extraction of caffeine from the two light-roasted coffee species;only arabica was favoured by medium roasting. The extraction pro-cess of dark-roasted coffee did not influence the release of thesecompounds. It is likely that, after the matrix is extensively ‘‘dam-aged” by the roasting process, the extraction of compounds is easierand occurs more or less independently of which process is used. Inthe case of the robusta coffee matrix, which was more sensitive todegradation, this behaviour was observed for some compounds evenin medium-roasted coffee.

Although the double-extraction process increased both the caf-feine and 5-CQA content of the light-roasted final product, this in-crease probably occurred in a different way for each compound.The 5-CQA is a thermolabile compound and was probably preservedin the first extraction stream at milder temperatures. As caffeine isthermostable, the double-extraction process may have released alarger amount of compounds from the light-roasted matrix. Con-cerning the behaviour of melanoidins, in general, their extractionwas favoured by the single-extraction process. Both the contentsand the composition of the higher molecular weight fraction, consid-ered to be melanoidins, are influenced by the roasting process andextraction conditions. As the molecular weight increases with thethermal treatment, severe conditions also result in the degradationof these compounds. Leloup (2006) evaluated the influence of tem-perature on the molecular weight profile of carbohydrates and ob-served the formation of mono- and disaccharides with increasingextraction temperature; however, under mild conditions, moleculesof over 10 kDa were formed. As two water streams are used in thedouble-extraction process, one with a higher temperature, com-pounds with higher molecular weights are probably degraded.

More 5-CQA and caffeine were extracted by the double-extrac-tion process, increasing the AA of the light-roasted product. Thisdemonstrates the effect of 5-CQA concentration on AA. For less in-

tense roasting systems, a process that yields higher concentrationsof 5-CQA is more advantageous. As this compound degrades andthe content of melanoidin increases, the extraction process has lessof an effect on AA.

Soluble coffee beverage thus possesses excellent antioxidantpotential, since its fabrication traditionally uses large amounts ofrobusta coffee and the extraction processes favour the enrichmentof components with antioxidant potential, such as 5-CQA andcaffeine.

4. Conclusion

All of the studied soluble coffee products possessed antioxidantpotential conferred by balanced concentrations of phenolic com-pounds, caffeine and melanoidins. AA was unaffected by roastingconditions, since the degradation of 5-CQA was balanced by theformation of melanoidins. The extraction process had a greaterinfluence on AA in lighter-roasted coffees. The higher caffeine con-tent of C. canephora resulted in products with greater AA, indicat-ing that the antioxidant activity of the final product dependsmainly on the species used in blends.

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