8
Eur Food Res Technol (2008) 227:1633–1640 DOI 10.1007/s00217-008-0887-x 123 ORIGINAL PAPER EVects of refrigeration and oxygen on the coVee brew composition Mónica Pérez-Martínez · Patricia Sopelana · M. Paz de Peña · Concepción Cid Received: 29 January 2008 / Revised: 18 April 2008 / Accepted: 4 May 2008 / Published online: 27 May 2008 © Springer-Verlag 2008 Abstract The aim of this work was to monitor the changes both in the composition and in some sensory parameters of Colombian Arabica coVee brews stored at room and refrigeration temperatures, with and without oxy- gen. Some nonvolatile compounds related to the taste of coVee brews were determined, in an attempt to study possi- ble relationships between chemical and sensory changes. Storage time hardly aVects the amounts of chlorogenic, caVeic and ferulic acids, reported to have some beneWcial health eVects, mainly due to their antioxidant activities. In contrast, pH decreases in all the coVee brews along the time, mainly in that stored at 25 °C with oxygen. The appearance of sourness and other non typical coVee tastes (rancid taste, aftertaste) and an increase in astringency leads to establish a shelf-life of 10 days for coVee brews stored at 25 °C with oxygen, 15 days for coVee brews stored at 4 °C with oxygen and at 25 °C without oxygen, and 20 days for coVee brews stored at 4 °C without oxygen. The behaviour of 5-caVeoylquinic acid, caVeic acid and 4-vinylguaiacol throughout time was diVerent from other studies conducted at higher temperatures to accelerate the staling, what reveals that stability studies of coVee brews should be made in real time and temperature. Keywords CoVee brew · Storage · Temperature · Oxygen · Shelf-life · Sensory analysis Introduction Nowadays, coVee is the second most consumed drink in the world after water [1] and more and more consumers demand its availability during the whole day. However, there are some situations when it is not possible to have the required equipment, such as a coVee maker and a heat source, or the time to prepare it. In collective catering, coVee brews are usually kept at high temperatures for a period of time; however, in more reduced Welds this option does not seem feasible or practical. Moreover, this is a solu- tion only for a few hours. Another possibility is the storage of coVee brews at refrigeration or at room temperatures, to be reheated, for example in a microwave oven, or to pre- pare cold coVee Although the shelf-life of coVee brews is very limited because of fungi development, it could maybe be possible to obtain fresh brews for commercial purposes, without any additives, if they are aseptically stored. Never- theless, it is well known that the storage of coVee beverages causes the deterioration of their sensory characteristics. Concretely, an increase in acidity has been observed in coVee beverages stored for a period of time, being this the most important factor in limiting their acceptability [25]. Acidity is an appreciated attribute of Colombian and other light roasted Arabica coVee brews. However, as time passes, this initial acidity is replaced by an excessively sharp, biting and unpleasant Xavour (such as vinegar or acetic acid), which is known as sourness [6, 7]. This latter should not be con- fused with the typical coVee acidity, but most of the papers use both terms without distinction. The increase of sourness in warm stored coVee brews has been attributed to the increase of acids produced by the hydrolysis of the quinic acid lactones and chlorogenic acid lactones formed during roasting, the hydrolysis of low molecular weight esters, and the thermal degradation of chlorogenic acids into their Part of this paper was presented at the 21st ASIC Colloquium, Montpellier, 2006. M. Pérez-Martínez · P. Sopelana · M. P. de Peña · C. Cid (&) Department of Nutrition, Food Science, Physiology, and Toxicology, School of Pharmacy, University of Navarra, 31080 Pamplona, Spain e-mail: [email protected]

Effects of refrigeration and oxygen on the coffee brew composition

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Page 1: Effects of refrigeration and oxygen on the coffee brew composition

Eur Food Res Technol (2008) 227:1633–1640

DOI 10.1007/s00217-008-0887-x

ORIGINAL PAPER

EVects of refrigeration and oxygen on the coVee brew composition

Mónica Pérez-Martínez · Patricia Sopelana · M. Paz de Peña · Concepción Cid

Received: 29 January 2008 / Revised: 18 April 2008 / Accepted: 4 May 2008 / Published online: 27 May 2008© Springer-Verlag 2008

Abstract The aim of this work was to monitor thechanges both in the composition and in some sensoryparameters of Colombian Arabica coVee brews stored atroom and refrigeration temperatures, with and without oxy-gen. Some nonvolatile compounds related to the taste ofcoVee brews were determined, in an attempt to study possi-ble relationships between chemical and sensory changes.Storage time hardly aVects the amounts of chlorogenic,caVeic and ferulic acids, reported to have some beneWcialhealth eVects, mainly due to their antioxidant activities. Incontrast, pH decreases in all the coVee brews along thetime, mainly in that stored at 25 °C with oxygen. Theappearance of sourness and other non typical coVee tastes(rancid taste, aftertaste) and an increase in astringency leadsto establish a shelf-life of 10 days for coVee brews stored at25 °C with oxygen, 15 days for coVee brews stored at 4 °Cwith oxygen and at 25 °C without oxygen, and 20 days forcoVee brews stored at 4 °C without oxygen. The behaviourof 5-caVeoylquinic acid, caVeic acid and 4-vinylguaiacolthroughout time was diVerent from other studies conductedat higher temperatures to accelerate the staling, whatreveals that stability studies of coVee brews should be madein real time and temperature.

Keywords CoVee brew · Storage · Temperature · Oxygen · Shelf-life · Sensory analysis

Introduction

Nowadays, coVee is the second most consumed drink in theworld after water [1] and more and more consumersdemand its availability during the whole day. However,there are some situations when it is not possible to have therequired equipment, such as a coVee maker and a heatsource, or the time to prepare it. In collective catering,coVee brews are usually kept at high temperatures for aperiod of time; however, in more reduced Welds this optiondoes not seem feasible or practical. Moreover, this is a solu-tion only for a few hours. Another possibility is the storageof coVee brews at refrigeration or at room temperatures, tobe reheated, for example in a microwave oven, or to pre-pare cold coVee Although the shelf-life of coVee brews isvery limited because of fungi development, it could maybebe possible to obtain fresh brews for commercial purposes,without any additives, if they are aseptically stored. Never-theless, it is well known that the storage of coVee beveragescauses the deterioration of their sensory characteristics.Concretely, an increase in acidity has been observed incoVee beverages stored for a period of time, being this themost important factor in limiting their acceptability [2–5].

Acidity is an appreciated attribute of Colombian and otherlight roasted Arabica coVee brews. However, as time passes,this initial acidity is replaced by an excessively sharp, bitingand unpleasant Xavour (such as vinegar or acetic acid), whichis known as sourness [6, 7]. This latter should not be con-fused with the typical coVee acidity, but most of the papersuse both terms without distinction. The increase of sournessin warm stored coVee brews has been attributed to theincrease of acids produced by the hydrolysis of the quinicacid lactones and chlorogenic acid lactones formed duringroasting, the hydrolysis of low molecular weight esters, andthe thermal degradation of chlorogenic acids into their

Part of this paper was presented at the 21st ASIC Colloquium, Montpellier, 2006.

M. Pérez-Martínez · P. Sopelana · M. P. de Peña · C. Cid (&)Department of Nutrition, Food Science, Physiology, and Toxicology, School of Pharmacy, University of Navarra, 31080 Pamplona, Spaine-mail: [email protected]

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1634 Eur Food Res Technol (2008) 227:1633–1640

corresponding hydroxycinnamic acids [8, 9]. However, mostof these conclusions have been obtained from the results of(a) accelerated ageing studies where coVee brews were main-tained at high temperatures (60–95 °C) [3, 4, 10–13], (b)studies of coVee beverages added with sugar and other addi-tives, and pasteurized, stored at room or refrigeration temper-atures [5, 14]; or (c) sterilized sugary coVee beverages storedat high temperature [15]. In all of them, an additional thermalprocess is included after coVee brew preparation, whichcould be relevant to the degradation of chlorogenic acids and,consequently to the coVee quality. Besides, in the scarcestudies where coVee beverages are stored at room or refriger-ation temperatures [5, 14], only a few parameters are consid-ered, mainly pH and other properties such as colour,electrical conductivity or optical density. In contrast, as far aswe know, no work about the changes undergone by sometypical components of coVee brews, such as caVeine, trigo-nelline or chlorogenic acids, in coVee brews stored at lowtemperatures has been carried out. These compounds arerelated to some sensory attributes of coVee brews, such asacidity, bitterness or astringency, whose intensiWcation isassociated with a loss of coVee brew quality. Thus, chloro-genic acids in general are known to be responsible for coVeeastringency [16] and their thermal degradation into caVeicand quinic acids also contributes signiWcantly to the develop-ment of acidity at elevated temperatures, causing the coVee tobecome acerbic (bitter and sour) [17]. Moreover, some phe-nolic compounds released during the thermal degradation ofchlorogenic acids, such as caVeic or ferulic acids, contributeto bitterness [18]. These latter can, in turn, act as precursorsof other compounds which also inXuence the Xavour ofcoVee brews, such as 4-vinylguaiacol [15].

On the other hand, the inXuence of oxygen on thechanges of coVee brews has only been studied focused onpH, colour and turbidity during hot storage [19–21]. There-fore, the aim of this study was to monitor the changes ofsome sensory and chemical parameters related to the tasteof coVee brews stored at room (25 °C) and refrigeration (4°C) temperatures. The advantages of the package inabsence of oxygen were studied too. Some microbiologicalparameters were also measured in order to guarantee thesafety of the stored coVee brews. These results constitute aWrst point for the development of coVee brews for commer-cial purposes, aseptically stored and with a longer shelf-life, destined for being consumed as hot coVee brews.

Materials and methods

Materials

Colombian Arabica ground roasted coVee was provided bya local factory.

Pure reference standards of caVeine, trigonelline, pent-oxyWlline, 5-caVeoylquinic acid (5-CQA), caVeic acid,ferulic acid and 4-vinylguaiacol were purchased fromSigma-Aldrich (Steinheim, Germany).

CoVee brew preparation

CoVee brews were prepared from 90 g of ground roastedcoVee for a water volume of 1 L, using French press coVee-makers. Extraction time was 3 min and water temperature90 § 2 °C (pH 7.0). The freshly prepared coVee brews wereimmediately poured into 330 mL sterilized glass Xasks,either up to a volume of 135 mL (with air headspace, this is,with oxygen) or up to the top (without air headspace, this is,without oxygen), and hermetically closed. The Wlling of theXasks was carried out aseptically in a laminar Xow cabin toavoid the microbiological contamination of the samples.Afterwards, both coVee brews bottled with and withoutoxygen were stored at 4 and 25 °C for 30 and 60 days,respectively.

Microbiological analysis

Aerobic mesophilic Xora was analysed by colony counttechnique at 30 °C (ISO 4833:2003). Enumeration of yeastsand molds was made by colony count technique at 25 °C(ISO 7954:1987).

CaVeine and trigonelline

Extract preparation, clean-up and HPLC analysis wereperformed following the method described by Maeztuet al. [22]. HPLC analysis was achieved with an analyticalHPLC unit (Agilent Technologies 1100), equipped with abinary pump and an automated sample injector. Areversed-phase Hypersil-ODS (5 �m particle size, 250 £4.6 mm) column was used. The mobile phase was acetoni-trile/water (15:85) in isocratic conditions at a constantXow rate of 2.0 mL/min at 36 °C during 15 min. Theinjection volume was 20 �L. Detection was accomplishedwith a diode-array detector, and chromatograms wererecorded at 280 nm.

5-CaVeoylquinic acid

500 �L of the coVee brew were diluted up to 50 mL withmilliQ water. 5-CQA HPLC analysis was carried out withthe same equipment described above. Acetonitrile andwater adjusted to pH 3.0 with a phosphoric acid solutionwere the solvents. The Xow conditions and the proportionof the solvents are shown in Table 1. The temperature ofanalysis was 25 °C and the injection volume 100 �L.Wavelength of detection was 325 nm. (Fig. 1).

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Eur Food Res Technol (2008) 227:1633–1640 1635

CaVeic acid, ferulic acid and 4-vinylguaiacol

The extraction, clean-up and HPLC analysis of these threecompounds were performed simultaneously, according tothe method developed by Álvarez-Vidaurre et al. [23]. TheHPLC analysis was carried out with the same equipmentdescribed above. The chromatographic separation wasachieved at 25 °C by using a complex gradient solvent sys-tem with acetonitrile/water adjusted to pH 2.5 with a phos-phoric acid solution (Table 2) [23]. Injection volume was100 �L. The wavelengths of detection were 314 nm forcaVeic acid, 325 nm for ferulic acid and 210 nm for 4-vinylguaiacol (Fig. 2).

pH

The measure was obtained with a Crison Basic 20pH-meter.

Sensory descriptive analysis

Twenty judges were recruited among members of theDepartment of Nutrition, Food Science, Physiology, andToxicology at the University of Navarra. Selection andtraining were carried out as described by Maeztu et al. [22]to have a ten-member panel. Although judges had experi-ence on sensory evaluation of coVee brews, they wereretrained during four sessions to adapt their evaluation tothe detection and quantiWcation of parameters related to

staling. Attention was focused in rancidity and the distinc-tion of acidity, typical from a Colombian coVee, and sour-ness, typical from an old coVee brew. Reference coVeebrews were prepared with a Colombian Arabica groundroasted coVee stored for 1–2 years for rancidity, otherstored for less than 1 month for acidity and the positiveXavours, and a coVee brew prepared with the same coVeebut stored for 1 month for sourness. A scorecard with themost frequently perceived sensory attributes was developedduring training. Two lines for “other” Xavours were added.Acidity, sourness, bitterness, astringency, rancidity andaftertaste were rated on 11-point scales from “none” (0) to“very high” (10).

Each coVee brew sample was heated in a microwaveoven at 90 § 2 °C immediately before tasting and servedmonadically in a white porcelain coVee cup. The order ofpresentation was randomized among sessions. A freshlyprepared coVee brew was evaluated at Wrst as a referenceand in order to avoid Wrst impressions. All evaluations wereconducted in isolated sensory booths illuminated withwhite light in the sensory laboratory under standardizedconditions by UNE 87-004-79 [24]. Rinse water was pro-vided between samples. After the individual evaluation of

Table 1 Flow and gradient solvent conditions for 5-caVeoylquinicacid HPLC analysis

Time (min)

Dilution (% acetonitrile:% water)

Flow (mL/min)

0 12.0:88.0 1.0

5 7.5:92.5 1.6

10 8.0:92.0 1.6

15 25.0:75.0 1.6

20 12.0:88.0 1.1

Fig. 1 HPLC chromatogram of 5-CQA

Time (min)

2,5 7,5 17,55 10 20 22,50

20

30

40

50

60

10

0

12,5 15

5-CQA

Abs

orpt

ion

mA

U (

325n

m)

Table 2 Flow and gradient solvent conditions for caVeic acid, ferulicacid and 4-vinylguaiacol HPLC analysis

Time (min)

Dilution (% acetonitrile:% water)

Flow (mL/min)

0–20 91:9 1.0

20–25 14:86 1.1

25–35 12:88 1.1

35–42 14:86 1.1

42–45 18:82 1.3

45–48 27:73 1.3

48–55 25:75 1.7

55–58 19:81 1.6

58–68 20:80 1.8

68–70 10:90 1.6

70–75 9:91 1.0

Fig. 2 HPLC chromatogram of caVeic acid, ferulic acid and 4-vinyl-guaiacol

0 10 20 30 40 50 60 70

0

200

400

600

8001000

1200

1400

Time (min)

Abs

orpt

ion

mA

U

Ferulic acidCaffeic acid 4-vinylguaiacol

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1636 Eur Food Res Technol (2008) 227:1633–1640

each sample, results were discussed and established bypanel consensus.

Statistical analysis

Each parameter was analysed in triplicate. Analysis of vari-ance (ANOVA) was applied for each storage temperature.The source of variation was the time. T-Tukey was appliedas the test a posteriori with a level of signiWcance of 95%.Student’s t-analysis was applied to the results obtained forboth storage temperatures. Correlations among variableswere assessed by means of the Pearson’s correlation test.All statistical analyses were performed using the SPSSv.11.0 software package.

Results and discussion

Neither aerobic mesophilic Xora nor molds and yeastsgrowth (<1 CFU) were observed in the coVee brews storedat 25 and 4 °C, both with and without oxygen, throughoutstorage time. Consequently, both coVee brews could beconsidered as stable products from the microbiologicalpoint of view.

As it is shown in Fig. 3, caVeine and trigonelline did notsuVer signiWcant changes along the time, neither due to thestorage temperature nor due to the presence of oxygen.

In Fig. 4, it is shown that the initial pH of the coVeebrews was between 5.1 and 5.2. An increase of chemicalacidity, measured by pH, was observed in all coVee brewsalong the time, being faster at 25 °C vs 4 °C and in oxygenpackaged coVee brews. Although both temperature and thepresence of oxygen inXuenced the pH decrease, the formerseemed to have higher incidence. These results partly agreewith those reported by Nicoli et al. [19] who found that thetemperature had a high inXuence on the pH decrease ofcoVee brews but the use of nitrogen hardly inXuenced thepH value.

Figure 5 shows the changes of 5-CQA, caVeic acid, feru-lic acid and 4-vinylguaiacol in coVee brews stored at 4 and

25 °C, with and without oxygen. A signiWcant increase (p <0.05) of 5-CQA during the Wrst 3 days of storage wasobserved for all coVee brews, except for that stored at 4 °Cwithout oxygen. In the latter, there was an initial decreasefollowed by an increase up to concentrations similar to theother coVee brews at 10 days. This increase could be due tothe hydrolysis of chlorogenic acid lactones formed duringthe roasting of coVee [8], or to the release of CQAs fromnon covalently linked polymeric skeletons, such as mela-noidins [25]. After this increase, 5-CQA was maintained upto 20 and 30 days when a decrease was observed in thecoVee brews stored without oxygen at 25 and 4 °C, respec-tively. It should be noticed that 5-CQA was signiWcantly (p< 0.05) higher in coVee brews stored at 25 vs 4 °C. In thecoVee brews stored without oxygen, the concentration ofcaVeic acid increased signiWcantly (p < 0.05) only duringthe Wrst day and smoothly decreased with time. In thosestored with oxygen, a maximum concentration of caVeicacid was observed at 25 °C before than at 4 °C. Theseincreases of caVeic acid might be originated by the hydroly-sis of CQAs, but not only 5-CQA, because there was nocorrelation between 5-CQA and caVeic acid changes. Onthe other hand, the presence of oxygen seems to have a rolein the formation, but also degradation, of caVeic acid whichneeds further investigation. The changes of these acids

Fig. 3 Changes in caVeine and trigonelline of coVee brews stored at 4 and 25 °C with and without oxygen

Caffeine

0

0.25

0.5

0.75

1

1.25

1.5

0 10 20 30 40 50 60

Time (days)

mg

/mL

Trigonelline

0

0.2

0.4

0.6

0.8

1

0 10 20 30 40 50 60

Time (days)

mg

/mL

4°C without O225°C with O24°C with O2 25°C without O2

Fig. 4 Changes in pH of coVee brews stored at 4 and 25 °C with andwithout oxygen

4.4

4.5

4.6

4.7

4.8

4.9

5

5.1

5.2

5.3

5.4

0 10 20 30 40 50 60

Time (days)

pH

4°C without O225°C with O24°C with O2 25°C without O2

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Eur Food Res Technol (2008) 227:1633–1640 1637

were in contrast with those observed in heat-maintainedcoVee brews [11] or in heat sterilized canned coVee bever-ages [15] where a decrease of 5-CQA was observed. Thisdecrease was attributed to isomerization of 5-CQA to 3-CQA and 4-CQA and to decomposition to caVeic and qui-nic acids. This diVerent behaviour could be due to the mildstorage temperatures used in our study which might be nothigh enough to induce the isomerization and degradation of5-CQA. Severini et al. [26] also found that the concentra-tion of chlorogenic acid hardly changed during the conser-vation of a coVee brew at 40 °C.

In Fig. 5 more changes in the concentration of ferulicacid in oxygen packaged coVee brews, and a less pro-nounced decrease in the coVee brews packaged withoutoxygen can be observed. This smooth evolution, at bothstorage temperatures, suggests a slight degradation of itsprecursors, feruloylquinic acids, which seem to be morestable than CQAs [27].

4-Vinylguaiacol is the product originated by the thermaldecarboxylation of ferulic acid. In aged canned beverages,such as coVee [15] and orange juices [28] it has beenreported as one of the most detrimental oV-Xavour com-pounds. However, in our study, the initial amount of 4-vinylguaiacol (3.92–3.95 �g/mL) showed a signiWcantdecrease during storage. This decrease was higher in coVeebrews stored with oxygen, maybe because 4-vinylguaiacolcould be oxidized to vanillin and vanillic acid [29], and alsoit was higher at 25 °C vs 4 °C. Therefore, this compoundseems not to be the main responsible for oV-Xavours incoVee brews stored at mild temperatures (room and refrig-eration). On the other hand, the diVerent behaviour of this

oV-Xavour compound at mild and high (60–80 °C) tempera-tures would question the conclusions derived of somekinetic studies [15] based on accelerated coVee ageingexperiments, because they might not be good predictors fornormal coVee beverages storage conditions (room or refrig-eration temperatures).

In Fig. 6, the changes in the taste sensory attributes ofthe studied coVee brews are shown. Acidity scores werehigh at the initial time with a tendency to decrease through-out storage. This decrease in perceived acidity apparentlycontrasts with the Wndings of other authors, who havereported an increase of acidity in coVee brews stored atroom temperature over a period of just 5 h [2, 30]. How-ever, the fall observed in this study must be interpreted as adisappearance of the typical acidity initially perceived inArabica coVee brews, being substituted by a sour taste [6].The members of the panel described sourness as “bad acid-ity” or “acidity non characteristic of coVee”, and it was per-ceived for the Wrst time at 15 days for coVee stored at 25 °Cwith oxygen, at 20 days for both coVee brews stored at 4 °Cwith oxygen and at 25 °C without oxygen, and at 30 daysfor coVee stored at 4 °C without oxygen. From these daysonwards, the judges not only perceived that sournessincreased with storage time, but also that the coVee brewbecame unacceptable from a sensory point of view. If dataconcerning pH are considered (see also Fig. 4), it can bechecked that, in the coVee brew stored at 25 °C with oxy-gen, this perception coincides with the moment when pHreaches a value of 4.8 (day 15). As early as 1972, Sivetz[31] proposed that the pH of beverages prepared from mildroasted coVee should be 4.9–5.2 and at pH · 4.8 the coVee

Fig. 5 Changes in 5-CQA, caVeic acid, ferulic acid and 4-vinylguaiacol of coVee brews stored at 4 and 25 °C with and without oxygen

5-CQA

0

0.2

0.4

0.6

0.8

1

0 10 20 30 40 50 60

Time (days)

mg

/mL

Caffeic acid

0

2

4

6

8

0 10 20 30 40 50 60

Time (days)

µg

/mL

Ferulic acid

0

2

4

6

8

0 10 20 30 40 50 60

Time (days)

µg

/mL

4-vinylguaiacol

0

2

4

6

8

0 10 20 30 40 50 60

Time (days)

µg

/mL

4°C without O225°C with O24°C with O2 25°C without O2

123

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1638 Eur Food Res Technol (2008) 227:1633–1640

tastes strongly sour and below 4.7 milk might be curdled.Moreover, the pH value of 4.8 has been considered as thelimit of acceptability for stored coVee brews by someauthors [3, 32]. It should be noticed that, in other studies[5], this pH was not reached after 50 days of storage at 25°C. This could be due to diVerences in the raw coVee used(a mixture of Arabica and Robusta 50:50), since coVees ofdiVerent origins provide extracts with diVerent pHs, andColombian is one of the most acidic [31]. The brewing pro-cedure or the storage conditions could also aVect the pHdecrease.

As it can be observed in Fig. 6, bitterness hardlychanged during the Wrst days but slightly tended to decreasewith time. This could be due to the little variationsobserved in nonvolatile compounds related to bitterness,such as caVeine, trigonelline, 5-CQA, caVeic and ferulicacids, even though a possible hydrolysis of chlorogenicacid lactones to chlorogenic acids might contribute to thedecreasing tendency. Related to this, Frank et al. [33] estab-lished the importance of the caVeoyl- and feruloyl-quinidesas well as more complex esters between quinides and cin-namoyl derivates as the most intense bitter taste compoundsin coVee brews.

Another cause of the quality loss of coVee brews is theappearance of unpleasant tastes such as astringency and

aftertaste which increased mainly during the Wrst days. ThecaVeic acid content was very high signiWcantly (p < 0.001)correlated with astringency (0.659) and 5-CQA contentvery high signiWcantly (p < 0.001) correlated with aftertaste(0.734). On the other hand, sourness was very high signiW-cantly (p < 0.001) correlated with pH values (¡0.841 and¡0.855 in coVee brews packed with and without oxygen,respectively). These results agree with those obtained byMaeztu et al. [22]. In contrast, the concentration of 5-CQAcontent was poorly correlated (p < 0.05) with sourness(0.554).

Taking the sensory results into account, shelf-life wastentatively established at 10 days for coVee stored at 25 °Cwith oxygen, 15 days for coVee brews stored at 4 °C withoxygen and at 25 °C without oxygen, and 20 days for coVeestored at 4 °C without oxygen. At these times, sourness andother non desirable coVee taste attributes such as rancidtaste, aftertaste and astringency were perceived by thepanel. It must be noticed that only for the coVee brewstored at 25 °C with oxygen, the shelf-life established bysensory analysis and the criterion of the pH value of 4.8 asthe limit of acceptance was coincident. However, in theother coVee brews, the shelf-life was established before pHreached this value. Consequently, the shelf-life calculationbased on the pH decrease kinetic and the pH value of 4.8

Fig. 6 Changes in taste sensory attributes of coVee brews stored at 4 and 25 °C with and without oxygen

Acidity

0

2

4

6

8

10

0 10 20 30 40 50 60

Time (days)

Sco

reS

core

Sourness

0

2

4

6

8

10

0 10 20 30 40 50 60

Time (days)

Sco

re

Bitterness

0

2

4

6

8

10

Sco

re

0

2

4

6

8

10

0 10 20 30 40 50 60

Time (days)

Astringency

0

2

4

6

8

10

Time (days)

0 10 20 30 40 50 60 0 10 20 30 40 50 60

0 10 20 30 40 50 60

Time (days) Time (days)S

core

Aftertaste Rancidity

0

2

4

6

8

10

Sco

re

4°C without O225°C with O24°C with O2 25°C without O2

123

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Eur Food Res Technol (2008) 227:1633–1640 1639

proposed as the “limit of acceptance” for stored coVee bev-erages by Dalla Rosa et al. [5], is not suitable to be appliedfor Colombian Arabica coVee brew. This might be becausethe pH established as the limit of acceptance should bediVerent for Arabica and Robusta coVee, or because pHshould not be considered as the unique criterion for coVeebrew acceptance.

Conclusions

The storage temperature and the packaging in presence orabsence of oxygen inXuence the changes not only of sometypical coVee components, but also of certain sensory char-acteristics. Thus, the maintenance of coVee brew at 25 °Cpackaged in the presence of oxygen, results in general, inmore accused and quicker changes in most of the parame-ters studied than the maintenance of coVee brew at 4 °Cpackaged in the presence of oxygen and at both tempera-tures packaged in the absence of oxygen. Even so, some ofthe compounds studied keep quite stable at the tempera-tures tested, mainly at 4 °C, which reveals that storage tem-perature is a key factor to reduce some of the changeswhich contribute to the deterioration of coVee brewsthroughout time. Besides, it could be added that a low stor-age temperature contributes to preserve the beneWcialeVects of coVee brews for human health, since some of thestudied compounds, such as 5-CQA or caVeic acid, havebeen reported to have antioxidant activity [34, 35].

Nevertheless, neither storage at refrigeration tempera-ture nor the absence of oxygen are eVective to avoid com-pletely the pH decrease and the development of sournessand other non desirable tastes in stored coVee brews.

The results of this study also reveal that the deteriorationof the coVee brews cannot be exclusively attributed eitherto the evolution of pH or to the studied compounds, andalso that pH is not the only factor which determines thelimit of acceptance of coVee brews. Consequently, furtherinvestigations should be carried out in order to know moredeeply which are the factors involved in the staling of thistype of product stored at room or refrigeration temperaturesand with or without oxygen.

Finally, the use of high temperatures to simulate anaccelerated ageing of coVee brews does not seem to be aproper way to study the evolution of this product duringstorage, since these temperatures favour reactions which donot occur at lower temperatures. It makes it necessary todevelop stability studies of coVee brews in real time andtemperatures.

Acknowledgments The authors thank the “Ministerio de Educacióny Ciencia” for the Wnancial support (AGL 2003-04045), for the grantgiven to M. Perez-Martinez and for the “Juan de la Cierva” contract

given to P. Sopelana. The authors also thank the members of the sen-sory panel, the Department of Microbiology at the University of Nava-rra for its technical assistance, and the Unión Tostadora, S.A., forproviding the coVee.

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