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Food Research International 40 (2007) 1170–1184

Optimisation of HS-SPME to study representativenessof partially baked bread odorant extracts

Pauline Poinot a,1, Joelle Grua-Priol a,2, Gaelle Arvisenet a,3, Cecile Rannou a,4,Michel Semenou b,5, Alain Le Bail a,6, Carole Prost a,*

a ENITIAA, UMR GEPEA CNRS 6144, Rue de la Geraudiere, 44322 Nantes Cedex 3, Franceb ENITIAA, UMR INRA Sensometrie et de Chimiometrie, Rue de la Geraudiere, 44322 Nantes Cedex 3, France

Received 18 June 2007; accepted 30 June 2007

Abstract

Head-space solid phase microextraction (HS-SPME) has been successfully applied to extract partially baked bread volatile com-pounds. During this study, three HS-SPME parameters (extraction time, extraction temperature, SPME fibre) were optimised on volatilecompounds extraction thanks to a representativeness analysis. Results displayed that a CAR/PDMS or a CAR/PDMS/DVB fibre asso-ciated with a time of 30 min or 60 min and a temperature of 35 �C allowed obtaining odorant extracts representative of the bread odour.A flash profile was then carried out to highlight the different flavour perceptions which could exist between these four extracts even if theywere close to the same bread odour. Completed by the analysis of their qualitative composition, the study revealed that there were someanalytical differences in odour perceptions. These differences may be linked to synergic effects caused by the presence of characteristicvolatile compounds in the extracts.� 2007 Elsevier Ltd. All rights reserved.

Keywords: Partially baked bread; Head-space solid phase microextraction; Odour representativeness; Flash profile; Volatile compounds

1. Introduction

Bread and cereal products constitute one of the mostconsumed foods in the world, under different forms depend-ing on cultural habits (Cayot, 2007; Pozo-Bayon, Guichard,& Cayot, 2006). Bread is considered as a traditional foodfor French population. Following consumers preferences,

0963-9969/$ - see front matter � 2007 Elsevier Ltd. All rights reserved.doi:10.1016/j.foodres.2007.06.011

* Corresponding author. Tel.: +33 2 51 78 55 17; fax: +33 2 51 78 55 20.E-mail addresses: pauline.poinot@enitiaa-nantes.fr (P. Poinot),

grua@enitiaa-nantes.fr (J. Grua-Priol), arvisenet@enitiaa-nantes.fr(G. Arvisenet), rannou.cecile@enitiaa-nantes.fr (C. Rannou), seme-nou@enitiaa-nantes.fr (M. Semenou), lebail@enitiaa-nantes.fr (A.L. Bail),prost@enitiaa-nantes.fr (C. Prost).

1 Tel.: +33 2 51 78 55 24.2 Tel.: +33 2 51 78 55 13.3 Tel.: +33 2 51 78 55 12.4 Tel.: +33 2 51 78 55 48.5 Tel.: +33 2 51 78 54 41.6 Tel.: +33 2 51 78 54 73.

a lot of studies have been carried out in order to improvebread texture, odour, flavour and bread shelf life (Barcenas,Haros, Benedito, & Rosell, 2003). Those studies result innew technologies which answer the increasing Europeandemand and reduce the complexity of the bakery process.Within this context, partially baked frozen and partiallybaked non-frozen breads have been developed in order tooffer consumers fresh bread at any time of the day (Barce-nas et al., 2003; Carr, Rodas, Della Torre, & Tadini,2006). Nowadays, they are found in supermarkets or in‘‘hot points’’ in down town and they have become key prod-ucts in term of innovation and feasibility (Carr et al., 2006).Indeed, these technologies permit to decrease wasted prod-ucts by adjusting the production to the demand of consum-ers. In addition, ‘‘hot points’’ permit to save manufacturingspace and to reduce the baking equipments needed to pre-pare the products before retailing (Carr et al., 2006).

Partially baked breads offer a lot of convenience and areleading products in term of market share among frozen and

P. Poinot et al. / Food Research International 40 (2007) 1170–1184 1171

non-frozen industrial breads. Partially bread making pro-cess differs from traditional baked making process. There-fore, differences in term of texture, taste, odour and flavourmay be expected in comparison to breads produced withconventional bread making process (Quılez, Ruiz, &Romero, 2006). These organoleptic properties greatly par-ticipate to the consumers acceptance of breads. Thus thestudy and the process control of the partially baked breadhas become an important stake for the baking industry.

Flavour is one of the main factors which influences con-sumers choices (Pozo-Bayon et al., 2006). Bread aroma hasbeen largely studied, and many methods have been devel-oped to identify the compounds responsible for its flavour(Cayot, 2007; Pozo-Bayon et al., 2006). More than 540 vol-atile compounds have been reported in the complex volatilefraction of bread (Ruiz, Quılez, Mestres, & Guasch, 2003).Quantitatively, the most important groups are alcohols,aldehydes, esters, ketones, acids, pyrazines and pyrrolines,but there are also furans, hydrocarbons, and lactones(Cayot, 2007; Pozo-Bayon et al., 2006; Seitz, Chung, &Rengarajan, 1998). However, only a small part of thesecompounds plays a significant role in the final bread aroma(Cayot, 2007; Pozo-Bayon et al., 2006). Scientists are nowinterested in investigating which of the volatile compoundsparticipate to the overall odour. Developments of extrac-tion methods and analytical techniques have then been car-ried out with the aim of identifying these volatilecompounds. The oldest technique used for the extractionof bread volatile compounds was solvent extraction (Rych-lik & Grosch, 1996; Schieberle & Grosch, 1994; Zehent-bauer & Grosch, 1998a, 1998b). Distillation (Ruiz et al.,2003) and vacuum distillation were more rarely employed(Frasse et al., 1992). Bread volatile compounds whichstrongly contribute to its global flavour were then charac-terised by coupling headspace with olfactometric methodsas Aroma Extract Dilution Analysis (AEDA) (Schieberle,1995). Solid-phase microextraction (SPME) is a particu-larly useful alternative method compared with otherswhich are more tedious or more expensive. SPME hasbecome one of the preferred techniques in aroma analysis,offering solvent free, rapid sampling with low cost and easepreparation. It is sensitive, selective and compatible withlow detection limits (Ho, Wan Aida, Maskat, & Osman,2006). Placed in the sample headspace, SPME is a non-destructive and non-invasive method to evaluate volatileand semi-volatile compounds (Ruiz et al., 2003). Head-Space SPME (HS-SPME) reproduces sniffing conditions(Costa Freitas, Parreira, & Vilas-Boas, 2001) and as itcould be used under low extraction temperature, it pro-vides a good estimation of the aroma profile as perceivedby the human nose (Ho et al., 2006). Extraction of volatilecompounds of a great number of foods was carried outusing HS-SPME extraction: palm sugar (Arenga pinnata)(Ho et al., 2006), cheese (Mallia, Fernandez-Garcia, &Olivier Bosset, 2005; Pinho, Peres, & Ferreira, 2003), cof-fees (Costa Freitas et al., 2001), ham (Garcia-Esteban,Ansorena, Astiasarran, Martin, & Ruiz, 2004), olive oils

(Cavalli, Fernandez, Lizzani-Cuvelier, & Loiseau, 2003),and wine (Baptista, Tavares, & Carvalho, 2001). Recently,the first extraction of partially baked frozen bread volatilecompounds was performed using HS-SPME (Ruiz et al.,2003). Volatile compounds released from several samplesof French partially baked baguettes after their extractionby HS-SPME were then analysed (Quılez et al., 2006).These studies permitted also to highlight the influence ofdifferent HS-SPME conditions on the bread volatile com-pounds trapping. To be reproducible and highly sensitive,HS-SPME extraction implies the control of many parame-ters, which could differ with the food matrix used. Themost influential parameters are among others extractiontemperature, equilibrium time, extraction time, fibre coat-ing. Within this context, Ruiz et al. (2003) showed that a75 lm CAR/PDMS (Carboxen/Polydimethylsiloxane)fibre, an extraction time of 60 min, a temperature of50 �C and a sample of 0.5 g in a 20 mL flask were, amongthe tested conditions, the ones which permitted to extractthe greatest quantity of volatile compounds.

If impacts of HS-SPME conditions on the quantitativeand qualitative release of partially baked frozen bread vol-atile compounds have been studied, the influence of thesecompounds on the global odour of HS-SPME extractshas not been investigated. An extraction method mustindeed produce extracts which have odorant characteristicsas close as possible to those of the corresponding food(Sarrazin, Le Quere, Gretsch, & Liardon, 2000). Thus thestudy of volatile extracts representativeness by comparingtheir odour to the one of the corresponding food, couldbe an accurate tool in order to validate the extraction tech-nique employed (Bernet, Dirninger, Etievant, & Schaeffer,1999; Le Pape, Grua-Priol, Prost, & Demaimay, 2004;Mehinagic, Prost, & Demaimay, 2003; Moio et al., 1995;Sarrazin et al., 2000; Varlet, Prost, & Serot, 2007).

The objective of this study is to determine the HS-SPMEconditions (fibre type, extraction time and extraction tem-perature) which permit to obtain volatile extracts represen-tative of the odour of the corresponding partially bakedbread. The present work extends the use of a factorial designin order to evaluate the odour representativeness of 27 vol-atile extracts obtained with three different fibres, associatedwith three different extraction temperatures and three differ-ent extraction times. Completed by a flash profile, the sen-sory differences between the samples whose odours wereestimated by a panel to be representative of the bread odourwere determined (Dairou & Sieffermann, 2002; Delarue &Sieffermann, 2004). The analysis of the bread volatile com-pounds of all volatile extracts was also assessed to link theirpresence in these samples with the sensory results.

2. Materials and methods

2.1. Chemicals

n-alcanes from octane to nonadecane came from Aldrich(Steinheim, Germany) except for octane, hexadecane,

Table 1The 27 HS-SPME conditions tested

Spme fibres (lm) (Supelco,Bellefonte, USA)

Extractiontimes (min)

Extractiontemperature (�C)

75 CAR/PDMS 15 2575 CAR/PDMS 15 3575 CAR/PDMS 15 5075 CAR/PDMS 30 2575 CAR/PDMS 30 3575 CAR/PDMS 30 5075 CAR/PDMS 60 2575 CAR/PDMS 60 3575 CAR/PDMS 60 50

100 PDMS 15 25100 PDMS 15 35100 PDMS 15 50100 PDMS 30 25100 PDMS 30 35100 PDMS 30 50100 PDMS 60 25100 PDMS 60 35100 PDMS 60 50

50/30 CAR/PDMS/DVB 15 2550/30 CAR/PDMS/DVB 15 3550/30 CAR/PDMS/DVB 15 5050/30 CAR/PDMS/DVB 30 2550/30 CAR/PDMS/DVB 30 3550/30 CAR/PDMS/DVB 30 5050/30 CAR/PDMS/DVB 60 2550/30 CAR/PDMS/DVB 60 3550/30 CAR/PDMS/DVB 60 50

Fibres: 75 lm Carboxen/Polydimethylsiloxane (CAR/PDMS); 100 lmPolydimethylsiloxane (PDMS); 50/30 lm Carboxen/Polydimethylsilox-ane/Divinylbenzene (CAR/PDMS/DVB).

1172 P. Poinot et al. / Food Research International 40 (2007) 1170–1184

octadecane and nonadecane which were from Sigma (SaintLouis, USA), hexane from Merck (Darmstadt, Germany),and pentadecane from Fluka (Steinheim, Germany). Etha-nol was purchased from Vermapur (Fontenay-sous-Bois,France). Standards were also employed for compoundsidentification. They were from Aldrich (Steinheim, Ger-many), except 1-propanol, 2,3-butanediol and the 2-meth-ylpropionic acid which were from Fluka (Buchs,Switzerland), 2,3-pentanedione from SAFC (Steinheim,Germany), and acetic acid from Panreac (Barcelona,Spain).

2.2. Bread sample

Commercial partially baked bread was used to carry outthe experiments. For each extraction condition, one halfbaguette was baked for 15 min and then cooled at roomtemperature for 30 min. It was then cut in slices andentirely crushed (crust and crumb). Six grams of crushedbread were weighed and placed in a 125 mL flask. A mag-netic stirring bar was also added in the flask which wasthen sealed with a silicone septum. The flask was immersedin a water bath whose temperature was controlled. In orderto evaluate the extraction temperature effect, three differenttemperatures were studied (Table 1). After 5 min equilib-rium, each of the tested fibres (Table 1) was exposed tothe sample headspace for one of the three extraction times(Table 1). Twenty-seven different extracts were thenassessed. During the extraction process, sample was contin-uously shaken with the magnetic stirring bar. At the end ofthe extraction time, the fibre was inserted into a gas chro-matograph (GC) injector port for thermal desorption ofthe extracted volatiles during 5 min.

2.3. GC-FID

Extracts collection as well as volatile compounds quan-tification were performed with a Varian Star 3400 GasChromatograph, coupled to a flame ionisation detector(FID) and a sniffing port. Volatile compounds were sepa-rated on a DB-WAX polar capillary column 30 m ·0.32 mm, 0.5 lm film thickness (J&W Scientific, Folsom,USA). Helium was used as the carrier gas with a flow rateof 1 mL min�1 (pressure: 75.8 kPa). The injector was at260 �C in split 1:1 mode for 2 min. It was then put in split-less mode until the end of the run time. The oven temper-ature program was held for 2 min at 45 �C, then increasedby 5 �C min�1 to 50 �C, by 0.5 �C min�1 to 51 �C, by8 �C min�1 to 170 �C, and then by 18 �C min�1 to230 �C. The sample was then held at 230 �C for 8 min(the total run time was 31.20 min).

2.4. Odour collection device

The collection of each HS-SPME volatile extract wasdone in a 100 mL glass gas syringe (Hamilton Gastight1000, Alltech, France) fitted with a valve (Mininert, All-

tech, France) and a Teflon end (Alltech, France). Beforethe injection of the extract in GC, a syringe was placedon a polyvalent syringe pump (VIT-FIT, Lambda, Switzer-land) and connected to the sniffing port placed at the end ofthe GC column using a glass column connector (UniversalQuick Seal, Varian, USA). Thanks to this device, half ofthe GC total flow (containing aroma compounds) waspulled to the FID detector, and the other half was pulledand collected in the syringe.

2.5. GC–MS analysis

The identification and quantification of volatile com-pounds were carried out with a Gas Chromatograph Agi-lent 6890 N coupled to a quadrupole mass detector (MS)Agilent 5973 Network. The GC program was the same asdescribed for GC-FID analysis. The injector temperaturewas set at 260 �C and mass detector at 250 �C. Volatilecompounds were pulled by a helium carrier gas with a flowrate of 3 mL min�1 (pressure: 62.4 kPa). The mass detectoroperated in scan mode, with electronic impact ioniza-tion (ionization energy 70 eV), and a mass range of33–300 amu and a scan rate of 2.72 scans s�1, used todetect the ions formed. Compounds identification wasbased on mass spectra identification (comparison with

P. Poinot et al. / Food Research International 40 (2007) 1170–1184 1173

standard MS spectra databases: Wiley 6), and standardsinjections.

2.6. Sensory analysis

2.6.1. Similarity and intensity testsThe panel was composed of nine judges (2 men and 7

women, aged from 25 to 50 years) from our researchdepartment. The panel has been previously trained during10 sessions to the quantification of similarity and intensitybetween a bread reference and samples belonging to theproduct space. The panel was also used to smell a gaseousodorant extract from gas syringes.

Two syringes were presented to the judges. The first onewas the reference and contained partially baked bread. Tobe in iso-intensity by comparison with the HS-SPME vola-tile extracts, it contained 0.5 g of crushed partially bakedbread. The other one was a volatile extract obtained underone of the HS-SPME conditions (Table 1). Judges wereasked to smell 10 mL of the two gaseous samples and toassess their odour proximity on a 100 mm scale, anchoredat the left end with ‘‘very different from the reference’’ andat the right end with ‘‘identical to the reference’’. They werealso asked to quantify the odour intensity of the extract bycomparison with the odour of the reference. A 100 mmscale anchored at the left end with ‘‘less intense than thereference’’, at the right end with ‘‘more intense than the ref-erence’’, and at the middle with ‘‘identical to the reference’’was used for extracts scoring.

Before the analysis of the representativeness of these 27different HS-SPME extracts, three of them were first pre-sented to the panellists three times, except for one judgewho appreciated one of these three samples two times.These three extracts corresponded to the association of a100 lm PDMS fibre with 15 min and 25 �C, and a 75 lmCAR/PDMS fibre with 30 min and 35 �C and finally a50/30 lm CAR/PDMS/DVB fibre with 60 min and 50 �C.The aim of this study was to verify the panel discriminativecapacity and its coherence.

2.6.2. Flash profile

The descriptive evaluation of volatile extracts was per-formed thanks to a flash profile. This sensory analysiswas performed in order to highlight odorant differencesbetween the samples found to be the closest to the odourof the bread reference, according to the previous similarityand intensity tests.

The panel dedicated to the flash profile was composed ofnine judges (1 man and 8 women, aged from 25 to 50 years)recruited in our research department. They were all experi-enced in sensory descriptive analysis.

The evaluation consisted in two individual sessions. Abrief outline of the procedures was previously given tojudges. During these two sessions, volatile extracts werepresented in gas syringes, obtained after their correspond-ing extraction.

During the first session, the gaseous samples were pre-sented simultaneously. After having smelt them, they wereasked to generate odorant attributes sufficiently different toallow a ranking of the samples. No limitation was givenregarding the number of sensory characteristics they couldgive. They were not allowed to generate hedonic terms.

All the sensory characteristics generated by the wholepanel were gathered in a single list. At the beginning ofthe second session, panellists were asked to read this listand to adapt their own list if they wished. The assessorswere then presented all the samples simultaneously andthey had to rank them along the sensory attributes belong-ing to their updated list. A 100 mm scale was then used,anchored at the left end with ‘‘attribute not perceived’’and at the right end ‘‘attribute very strongly perceived’’.Judges could give the same score to several samples. Forthe two sessions, judges could smell the samples as muchas they wanted and could take time they needed to evaluatethem.

2.7. Statistical analysis

Judges performance was first verified thanks to an anal-ysis of variance (ANOVA) on the odour similarity andintensity scores given to the three repeated samples.

The same statistical test was carried out on scores givento the 27 samples to identify if there was a sample effect onodour similarity and intensity, and then to determine theeffects of the three factors (SPME fibre, extraction timeand extraction temperature) and their interactions. Possiblesignificant differences between the mean scores obtained foreach sample were evaluated by least significant differences(LSD) multiple comparison tests with a confidence levelof 95%.

PCA was applied to the data from flash profile to assessthe semantic interpretation and to characterise samples dif-ferences. Only attributes characterised by a correlation dis-tance to the sensory map superior to 0.8 were used todescribe the samples.

A PCA was also performed on the relative area countsobtained for each aromatic extract. This final step allowedus to link the sensory data to the analytical ones.

3. Results and discussion

3.1. Odour representativeness

3.1.1. Panel performance

Both judges and samples effects were evaluated thanksto the three repeated samples. Results are presented firston the odour similarity (Table 2), and then on the odourintensity (Table 3).

The ANOVA showed that judges were able to discrimi-nate different samples in terms of odour similarity andodour intensity at a confidence level of 95% (Tables 2and 3). Indeed, for both similarity and intensity tests,P-values corresponding to the samples effects were below

Table 2Multiway ANOVA on odour similarity scores given to the three repeatedsamples

Source Sum of squares Df Meansquare

F-ratio

P-value

Main effects

A: Judges 105.657 8 13.2071 4.21 0.0006B: Samples 451.596 2 225.798 71.94 0.0000

Interactions

AB 70.5764 16 4.41103 1.41 0.1753Residual 166.345 53 3.13858Total

(corrected)797.375 79

All F-ratios are based on the residual mean square error.

Table 3Multiway ANOVA on odour intensity scores given to the three repeatedsamples

Source Sum of squares Df Meansquare

F-ratio

P-value

Main effects

A: Judges 31.2528 8 3.90659 2.86 0.0102B: Samples 225.414 2 112.107 82.47 0.0000

Interactions

AB 31.3828 16 1.96142 1.44 0.1615Residual 72.4317 53 1.36664Total

(corrected)362.327 79

All F-ratios are based on the residual mean square error.

Table 4Multiway ANOVA on the judge’s scores given to the 27 HS-SPMEextracts according to their odour similarity and odour intensity

Sensory test Df Odour similarity Odour intensityMain effects P-value P-value

A: Judges 8 0.0000 0.0000B: Samples 26 0.0000 0.0000

For each analysis, a significant level of 5% (or P-value = 0.05) wasconsidered.

Table 5

1174 P. Poinot et al. / Food Research International 40 (2007) 1170–1184

5%. The results reported in Tables 2 and 3 also demon-strate that there were judge’s effects on odour similarityand odour intensity scores while there was no interactionbetween ‘‘judges · samples’’ factors. An absence of a signif-icant interaction between these two factors revealed thatjudge’s effects were only due to a different use of scale bythe panellists. Indeed, some of them could score the sam-ples on the overall length of the scale, while others onlyused a little part of the scale. It was also possible that someof them tended to score the samples on the right part of thescale, whereas others were inclined to give low notes to allthe samples. This could be linked to judge’s subjectivityconcerning their similarity judgement. Thus there was aconsensus between panellists, and they perceived in thesame way the odour similarity and the odour intensity ofthe different extracts.

Multiway ANOVA of HS-SPME conditions effects on odour similarityand odour intensity scores

Sensory test Odour similarity Odour intensityEffects P-value P-value

A: Fibres 0.0000 0.0000B: Extraction time 0.0001 0.0000C: Extraction temperature 0.0007 0.0544AB 0.2353 0.0079AC 0.0986 0.0175BC 0.0045 0.0909

For each analysis, a significant level of 5% (or P-value = 0.05) wasconsidered.

3.1.2. Extracts representativeness

Twenty-seven different extracts were presented to thepanel who was asked to quantify the odour similarityand intensity between each extract and the bread referenceon two 100 mm scales.

ANOVA and LSD tests on judge’s scores given to the 27extracts according to their odour similarity and their odourintensity were first performed (Table 4). The samples effectand the judges effect were thus studied. The results showedthat there was a samples effect at a significant level of 5%.

Thus, the odour and the intensity of the 27 extracts pre-sented were different from one another. It could then beassumed that different HS-SPME conditions led to samplesmore or less close to the initial product, either in odoursimilarity or in odour intensity. As it was demonstratedbefore, the judge’s effect was only due to the different useof scales by the panellists.

The effect of the three SPME parameters tested (fibretype, extraction time and extraction temperature) on theodour extract representativeness were then assessed (Tables5 and 6).

The fibre type and the extraction time influenced theodour similarity and the odour intensity of the extractedsamples. Seventy-five micrometer CAR/PDMS and 30/50 lm CAR/PDMS/DVB fibres allowed obtaining volatileextracts close to the odour of the bread reference in termsof odour similarity and odour intensity. This could be dueto the trapping sensitivity of these two fibres in regard tothe one of the 100 lm PDMS. Indeed the 100 lm PDMSpreferentially traps non-polar compounds (Bicchi et al.,2005; Bicchi, Cordero, & Rubiolo, 2004; Guerrero, Marin,Mejias, & Barroso, 2006; Tienpont, David, Bicchi, & San-dra, 2000; Zuin et al., 2006), while the two others are com-posed of polymeric multiphases which permit them to trapnon-polar and polar compounds. The different nature oftheir phases could then explain the low quantity of breadvolatile compounds trapped on the 100 lm PDMS fibreand thus a low intensity and a low representativeness ofthe corresponding extracts.

The extraction time effect revealed that extracts obtainedfor 30 or 60 min extraction time were characterised by anodour and intensity closer to the reference one. Thus, anextraction time of 15 min was not sufficient to trap breadvolatile compounds.

Table 6Graphs of the effects of the three HS-SPME factors on odour similarity and odour intensity scores

Effect Odour similarity Odour intensity

A: Fibre

B: Extraction time

C: Extraction temperature No significant effect

For each analysis, a significant level of 5% (or P-value = 0.05) was considered.

P. Poinot et al. / Food Research International 40 (2007) 1170–1184 1175

The extraction temperature had only a significant effecton the odour similarity. An extraction temperature of25 �C did not allow obtaining volatile extracts similar tothe bread odour reference. An explanation of this effectcould be the absence of volatilisation of heavy molecularcompounds when low temperature was applied. Thus onlya small part of bread volatile compounds were trapped onSPME fibres. An extraction temperature of 35 �C permit-ted to obtain volatile extracts which were representativeof the bread odour reference. A higher temperature of50 �C allowed obtaining extracts which were as intensiveas the reference but characterised by an odour differentfrom the bread one. The formation and the release of addi-tional compounds under this temperature, like Maillardvolatile compounds, could explain the low representative-ness of the corresponding extracts.

A significant interaction between the extraction time fac-tor and the extraction temperature factor occurred for theodour similarity (Tables 5 and 7). This interaction revealedthat volatile extracts were significantly closer to the breadodour reference when a temperature of 35 �C was associ-ated to a time of 30 min whatever the fibre type was.

Odour intensity was influenced by an interactionbetween the fibre factor and the extraction time factor, aswell as between the fibre factor and the extraction temper-ature factor. The first interaction indicated that a 75 lmCAR/PDMS fibre associated with an extraction time of30 min or 60 min led to volatile extracts closer to the refer-ence in terms of intensity. The same results were obtainedwith a 50/30 lm CAR/PDMS/DVB fibre. The secondinteraction revealed that a 75 lm CAR/PDMS or a 50/30 lm CAR/PDMS/DVB fibre associated with an extrac-tion temperature of 35 �C or 50 �C permitted to obtain vol-atile extracts which were characterised by higher intensity.

The LSD test which was realised after the one-wayANOVA performed on the means judge’s scores obtainedfor each sample, permitted to differentiate and rank the27 volatile samples according to their odour similarity tothe bread reference (Fig. 1). The same study was under-taken on their odour intensity proximity (Fig. 2).

The results shown in Fig. 1 illustrated the previousANOVA analysis. Indeed, four extracts had odorant char-acteristics close to the ones of the bread reference andbelonged to the first LSD group. These extracts were

Table 7Graphs of the interactions of the three HS-SPME factors on odour similarity and odour intensity scores

Interaction Odour similarity Odour intensity

AB: Fibre/time No significant effect

Fibre

Odo

ur in

tens

ity s

core

s

Time15 min30 min60 min

1.31.82.32.83.33.84.3

CAR/PDMS PDMS CAR/PDMS/DVB

AC: Fibre/temperature No significant effect

Fibre

Odo

ur in

tens

ity s

core

s

Temperature25°C35°C50°C

1.11.62.12.63.13.64.1

CAR/PDMS PDMS CAR/PDMS/DVB

BC: Time/temperature

Time

Odo

ur s

imila

rity

scor

es Temterature25°C35°C50°C

3.1

4.1

5.1

6.1

7.1

15 min 30 min 60 min

FibreNo significant effect

For each analysis, a significant level of 5% (or P-value = 0.05) was considered.

Odour similarity

0

1

2

3

4

5

6

7

8

9

10

CAR

/PD

MS

- 30m

in -

35°C

CAR

/PD

MS/

DVB

- 30

min

- 35

°C

CAR

/PD

MS

- 60m

in -

35°C

CAR

/PD

MS/

DVB

- 60

min

- 35

°C

CAR

/PD

MS

- 60m

in -

50°C

CAR

/PD

MS

- 60m

in -

25°C

CAR

/PD

MS/

DVB

- 30

min

- 50

°C

CAR

/PD

MS

- 15m

in -

25°C

CAR

/PD

MS/

DVB

- 60

min

- 50

°C

CAR

/PD

MS/

DVB

- 15

min

- 50

°C

CAR

/PD

MS/

DVB

- 60

min

- 25

°C

CAR

/PD

MS

- 30m

in -

50°C

PDM

S - 3

0min

- 35

°C

CAR

/PD

MS/

DVB

- 15

min

- 35

°C

CAR

/PD

MS/

DVB

- 30

min

- 25

°C

CAR

/PD

MS

- 15m

in -

35°C

CAR

/PD

MS

- 30m

in -

25°C

CAR

/PD

MS/

DVB

- 15

min

- 25

°C

PDM

S - 3

0min

- 50

°C

CAR

/PD

MS

- 15m

in -

50°C

PDM

S - 6

0min

- 25

°C

PDM

S - 6

0min

- 35

°C

PDM

S - 3

0min

- 25

°C

PDM

S - 1

5min

- 25

°C

PDM

S - 1

5min

- 35

°C

PDM

S - 6

0min

- 50

°C

PDM

S -1

5m

in -

50°C

Extracts

Scor

es

Identical to the reference

Very different fromthe reference

Fig. 1. Means graph with confidence intervals level of 95% on judge’s scores given to the 27 HS-SPME extracts for odour similarity; j: samples whichbelonged to the first LSD group at a confidence level of 95%.

1176 P. Poinot et al. / Food Research International 40 (2007) 1170–1184

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Scor

esMore intense

than the reference

Identical to the

reference

Less intense than the

reference

Fig. 2. Means graph with confidence intervals level of 95% on judge’s scores given to the 27 HS-SPME extracts for odour intensity; j: samples whichbelonged to the first LSD group at a confidence level of 95%.

P. Poinot et al. / Food Research International 40 (2007) 1170–1184 1177

obtained with a 75 lm CAR/PDMS fibre associated withan extraction temperature of 35 �C and an extraction timeof 30 min or 60 min (noted CAR/PDMS-30 min-35 �C andCAR/PDMS-60 min-35 �C). In the same way, a 30/50 lmCAR/PDMS/DVB fibre, associated with an extractiontime of 30 min or 60 min, and an extraction temperatureof 35 �C led to extracts which were close to the odour ofthe bread reference (noted CAR/PDMS/DVB-30 min-35 �C and CAR/PDMS/DVB-60 min-35 �C). Moreover, itcould be seen in Fig. 1 that extracts obtained for 30 minwere closer from the reference than the two ones obtainedwith an extraction time of 60 min.

According to Fig. 2, the extracts which had an odourintensity close to the odour intensity of the bread referencealso corresponded to the HS-SPME conditions determinedafter the ANOVA analysis (Tables 5–7). Six HS-SPMEextracts had an odour intensity close to the reference andbelonged to the first LSD group.

Within the first LSD group obtained for the odourintensity test, three extracts were also determined to havean odour similarity close to the bread reference. CAR/PDMS-30 min-35 �C and CAR/PDMS-60 min-35 �C vola-tile extracts were, indeed, representative of the odour ofbread. CAR/PDMS/DVB-60 min-35 �C also led to extractswhich were close to the bread odour reference in terms ofodour similarity and odour intensity. Even if the intensityof the CAR/PDMS/DVB-30 min-35 �C sample was a littleless intense than the one of the three extracts cited before

(this extracts belonged to the second group of the intensityLSD test), it could also be considered to be representativeof the bread odour because of its high score obtained forthe odour similarity test.

Thus, four different SPME conditions led to volatileextracts which were representative of the bread odour ref-erence in terms of odour similarity and odour intensity.The study of the qualitative composition of the 27 sampleswas then undertaken in order to explain their differentodorant perceptions. It consisted in identifying volatilecompounds present in the samples as well as in quantifyingtheir relative amount. Volatile compounds identified in the27 extracts are presented in Table 8.

A PCA was then performed on the relative area countsof volatile compounds identified under each condition. Wenoted a good inertia of PCA formed by the two first axeswhich explained 70.8% of total information. Each dimen-sion was correlated with different bread volatile com-pounds. The correlation plot (Fig. 3) showed that thefirst axis opposed ethanol to the other compounds, espe-cially to 2-ethoxy-1-propanol, 2-methylpyrazine, furfural,butyric acid, dihydro-2-methyl-3(2H)-furanone, 2,3-pen-tanedione, 5-methyl-2-furfural, hexanal and pyrrole.

The second dimension was negatively correlated with2-methylpropanal, 3-methylbutanal, 1-propanol, and2-methyl-1-propanol (Fig. 3).

Fig. 4 shows the representation of the 27 extracts on thisbidimensional plot. This plot displays that extracts

Table 8Volatile compounds identified in the 27 bread odorant HS-SPME extracts

CASnumber

Volatile compounds Odorant attributes

78-84-2 2-Methylpropanal Maltyb,c

96-17-3 2-Methylbutanal Maltyb,c

590-86-3 3-Methylbutanal Maltyb,c,d

64-17-5 Ethanol Alcoholica

431-03-8 2,3-Butanedione Buttera,b,c,d

71-23-8 1-Propanol Alcoholica

600-14-6 2,3-Pentanedione Butterb,c

66-25-1 Hexanal Greenb,c,d, grassa, fata

78-83-1 2-Methylpropanol Alcoholica, wine likea

1569-02-4 1-Ethoxy-2-propanol111-13-7 2-Heptanone Fruitya, cinnamona

123-51-3 3-Methyl-1-butanol Maltyb,d alcoholicb,d

3777-69-3 2-Pentylfuran Fruitya

71-41-0 1-Pentanol Fusel-like sweeta

109-08-0 2-Methylpyrazine Burnta, sweeta

513-86-0 3-Hydroxy-2-butanone Buttera, yoghurta, creama

3188-00-9 Dihydro-2-methyl-3(2H)-furanone

Rancida, buttera

111-27-3 1-Hexanol Grassa, woodya, milda,sweeta

64-19-7 Acetic acid Acida,b, pungenta,b, soura,b

98-01-1 Furfural Burnta

109-97-7 Pyrrole Burnta, sweeta

1192-62-7 2-Acetylfuran Smokyb, roastyd

513-85-9 2,3-Butanediol620-02-0 5-Methyl-2-furfural Bitterb,c, almondb,c, sweeta

107-92-6 Butyric acid Rancida,b, sweatyb

98-00-0 Furfuryl alcohol Milda, warm oilya, burnta

a Fenaroli (2002).b Pozo-Bayon et al. (2006).c Rychlik and Grosch (1996).d Schieberle and Grosch (1994).

1178 P. Poinot et al. / Food Research International 40 (2007) 1170–1184

obtained with a 100 lm PDMS fibre were characterised bya higher quantity of ethanol and a lesser extent of the othercompounds (dot circle). This result could be explained bytwo facts. One explanation could refer to the abundanceof ethanol in the initial bread samples. Thus, despite itspolar nature, ethanol was trapped in high quantity on thisfibre. The second reason could be the low affinity of theother bread volatile compounds for this fibre. As a result,except ethanol, little amounts of volatile compounds weretrapped on it, which may explain the low similarity andintensity scores given to these samples.

30/50 lm CAR/PDMS/DVB fibre permitted to extracthigher quantity of Maillard volatile compounds than75 lm CAR/PDMS and 100 lm PDMS fibres. Theseresults agree with the ones found by Rega, Guerard, Maire,and Giampaoli (2006) and Moon, Cliff, and Li-Chan(2006), who demonstrated that a CAR/PDMS/DVB fibreallowed to extract Maillard compounds in high amounts.The formation and the release of such volatile compoundsoccurred under high temperature (50 �C) or/and long time(60 min). Thus, under these conditions, Maillard reactionmay happen in bread samples, leading to the formation

of furfural and furan derivatives which result in a loss ofbread samples water (Pozo-Bayon et al., 2006).

The results also revealed that for three of the four HS-SPME conditions determined to be representative of thebread odour, the corresponding extracts had a close quali-tative composition. Moreover, their composition differedfrom the one of the other extracts. These extracts corre-sponded to CAR/PDMS-30 min-35 �C, CAR/PDMS-60 min-35 �C and CAR/PDMS/DVB-30 min-35 �C. Itcould then be suggested that a representative odorantextract was characterised by a particular qualitative com-position, which was only obtained under these three extrac-tion conditions (continuous line). The three extracts wereessentially represented on the second dimension. Their con-tribution to its global inertia was, respectively of 11.1% forCAR/PDMS-30 min-35 �C, of 9% for CAR/PDMS-60 min-35 �C and 4.5% for CAR/PDMS/DVB-30 min-35 �C. These extracts were characterised by higher relativeamounts of 2-methylpropanal, 3-methylbutanal, 1-propa-nol, and 2-methyl-1-propanol (Figs. 3 and 4). It could alsobe mentioned that they tended to contain 3-methyl-1-buta-nol, 2-methylpropanol, 2-methylbutanal, 3-hydroxy-2-butanone and 2,3-butanedione in a relative high amount,while they were composed of medium quantity of ethanol.2-methylbutanal, 3-methylbutanal, and 2-methylpropanalare Strecker aldehydes and they are characterised by amalty odour (Table 8). Associated with buttery andalcoholic notes, given by 2,3-butanedione and 3-hydroxy-2-butanone on one hand, and by the 1-propanol and2-methylpropanol on the other hand, they may conductto a mix characterised by a bread odour. Nevertheless, itmust not be forgotten that an odour is a result of interac-tions between volatile compounds. Thus high quantities ofthese volatile compounds in volatile extracts were not theonly reasons to their bread odour. Indeed, these volatilescompounds interacted with others which were present inlower concentrations. It was the resulted mix which con-ducted to a bread odour.

The last extract determined to be representative ofthe bread odour was not characterised by the same qual-itative composition. Indeed CAR/PDMS/DVB-60 min-35 �C extract was essentially correlated with the firstdimension (Fig. 4). Its inertia contribution was of 13%.Thus, this extract was composed of lower quantity ofethanol than the other samples, and higher relative quan-tity of furan derivatives (dihydro-2-methyl-3(2H)-fura-none, 5-methyl-2-furfural and furfural) and pyrrole,butyric acid, 2-ethoxy-1-propanol, 2-methylpyrazine, hex-anal, and 2,3-pentanedione. It may also be assumed thata bread odour could be obtained when Maillard com-pounds as furan derivatives, 2-methylpyrazine and pyrrolewhich are characterised by burnt and sweet notes arepresent in high relative quantity with fatty and greennotes given by 2,3-pentanedione, hexanal, and butyricacid compounds (Table 8).

To conclude, four volatile extracts were then found to beclose to the bread odour. According to the study of their

2-Methylpropanal3-Methylbutanal

2,3-Butanediol

Acetic acid

Ethanol

1-Pentanol1-Hexanol

2-Pentylfuran

Furfuryl alcohol Pyrrole2-Heptanone Hexanal

Butyric acid2-Methylpyrazine

5-Methyl-2-furfural

2-Acetylfuran

Furfural1-Ethoxy-2-

propanol

Dihydro-2-methyl-3(2H)-furanone

2,3-Pentanedione3-Hydroxy-2-

butanone2,3-Butanedione3-Methyl-1-butanone

2-Methylbutanal1-Propanol2-Methyl-1-propanol

PC 1 - 51.3%

PC 2

- 19

.5%

Fig. 3. Correlation plot of qualitative data obtained for the 27 HS-SPME extracts in the two first dimensions.

PDMS- 30 min - 35°C

PDMS- 60 min - 35°C

PDMS- 30 min - 50°C

PDMS- 60 min - 50°C

PDMS- 15 min - 25°CPDMS- 15 min - 50°C

PDMS- 15 min - 35°CPDMS- 60 min - 25°C

PDMS- 30 min - 25°C

CAR/PDMS- 15 min - 25°

CAR/PDMS- 15 min - 35°C

CAR/PDMS- 30 min - 25°C

CAR/PDMS- 30 min - 50°C

CAR/PDMS/DVB- 15 min - 35°C

CAR/PDMS- 15 min - 50°C

CAR/PDMS- 60 min - 25°C

CAR/PDMS/DVB- 15 min - 25°C

CAR/PDMS- 30 min - 35°CCAR/PDMS- 60 min - 35°C

CAR/PDMS/DVB- 30 min - 25°C

CAR/PDMS/DVB- 60 min - 25°C

CAR/PDMS/DVB- 30 min - 35°C

CAR/PDMS- 60 min - 50°C

CAR/PDMS/DVB- 15 min - 50°C

CAR/PDMS/DVB- 60 min - 35°C

CAR/PDMS/DVB- 60 min - 50°C

CAR/PDMS/DVB- 30 min - 50°C

-4

-2

0

2

4

-5 -2 1 4 7CP 1 - 51.3%

CP

2 - 1

9.5%

Fig. 4. HS-SPME extracts plot according to their qualitative composition in the two first dimensions; . . .. . .: Extracts obtained with a 100 lm PDMS fibre;—: Three of the four extracts considered to be representative of the bread odour; - - - -: The fourth sample considered to be representative of the breadodour.

P. Poinot et al. / Food Research International 40 (2007) 1170–1184 1179

1180 P. Poinot et al. / Food Research International 40 (2007) 1170–1184

qualitative composition, three of these four extracts werecharacterised by a quite similar qualitative compositionbased on higher amounts of certain Strecker aldehydes,2,3-butanedione, 1-propanol, and 2-methylpropanol. Theother HS-SPME conditions led to a different qualitativecomposition, characterised by a lower quantity of ethanol,and higher quantities of Maillard furan derivatives (furfu-ryl alcohol and 2-pentylfuran), pyrrole and hexanal. Whilethese extracts were close to the bread odour, their differentqualitative composition could result in different consumersflavour perceptions. To analyse these sensory differencesmore precisely, a flash profile was conducted on these fourextracts.

3.2. Flash profile

A flash profile was performed in order to get someinsights of the four optimum bread extracts flavour percep-tions. 32 attributes were generated by the panel (Table 9).

A PCA was performed to characterise the four extractsaccording to the odorant descriptors generated by all thepanellists. Fig. 5 displays the configuration obtained byPCA. The examination of the correlation plot indicates

Table 9Odorant attributes mentioned by the flash profile panel

Individual attributes Number of quotations

Acid-sour 1Alcohol 1Anise 2Butter 4Rusk 1Brioche 1Cocoa 3Caramel 4Cardboard 3Cereal 1Crust 1Mild-sweet 1Flour 5Cake 2Roasted 4Wet grass 1Fat oil 1Linseed oil 2Yeast 1Bread crumb 2Hazelnut 2Walnut 1Bakerie odour 1Bread 4Sandwich loaf 1Commercial bread 1Toasted bread 1Dough 1Foot 5Hot-Spicy 1Fish 1Sweet 1Vanilla 2

that the two first principal dimensions explained 73.4% ofthe total variance. Because of a different number of termsgenerated by each judge, and because of the difficulty tointerpret them, only the attributes with an absolute corre-lation value higher than 0.8 were retained for the interpre-tation of the two first axes.

According to this correlation plot, the first dimensionwas essentially positively associated with ‘‘Roasted’’, ‘‘Car-amel’’ and ‘‘Cocoa’’ attributes. It was negatively correlatedwith attributes which could be gathered under ‘‘Rough’’notes. The second one appeared to be the contrast between‘‘Bread’’, ‘‘Fatty’’ and ‘‘Sweet’’ notes, and ‘‘Rancid’’ and‘‘Wet’’ descriptors group.

As it can be seen in Fig. 6, the samples were character-ised by several attributes groups. They were distinctlyplaced in each quarter of the product plot. According toits right bottom position, CAR/PDMS-30 min-35 �C sam-ple was characterised by ‘‘Roasted’’ and ‘‘Toasted bread’’attributes as well as ‘‘Caramel’’ and ‘‘Cocoa’’ notes.CAR/PDMS/DVB-30 min-35 �C extract, localised on theleft top quarter, was perceived to have both ‘‘Bread’’,‘‘Fatty’’ and ‘‘Sweet bakeries’’ notes. CAR/PDMS-60 min-35 �C extract tended to have ‘‘Bread’’, ‘‘Cake’’and ‘‘Buttery’’ notes. Finally, CAR/PDMS/DVB-60 min-35 �C sample was essentially characterised by ‘‘Green’’,‘‘Fresh’’ and ‘‘Oily’’ attributes. It could be noticed thatCAR/PDMS-30 min-35 �C, CAR/PDMS-60 min-35 �Cand CAR/PDMS/DVB-30 min-35 �C samples were allcharacterised by close attributes which could be gatheredunder ‘‘Bread’’ and ‘‘Sweety’’ notes. This could be due totheir qualitative compositions which are quite similar (Figs.3 and 4). Nevertheless, as these samples were characterisedby different sensory descriptors by the panellists, it could bethought that little qualitative differences existed betweenthem.

This is shown on Figs. 7 and 8 which display the quali-tative composition of the four representative extracts aftera PCA. The two first principal dimensions accounted forabout 88% of the total variance.

It could be seen that CAR/PDMS-30 min-35 �C samplewas composed of higher quantities of ethanol (alcohol),3-methylbutanal (malty) and 2-methylpropanal (malty)than the three others. It could then be supposed that higheramount of these three components could lead to a breadodour containing also ‘‘Roasted’’, ‘‘Caramel’’ and‘‘Cocoa’’ attributes. Following the first dimension, thisextract was opposed to the CAR/PDMS/DVB-60 min-35 �C extract. As it was shown in Fig. 4, its qualitativecomposition was really different from the others. Thiscould be the result of its odorant specificity which wascharacterised by ‘‘Green’’, ‘‘Fresh’’ and ‘‘Oily’’ notes.CAR/PDMS-60 min-35 �C and CAR/PDMS/DVB-30 min-35 �C samples were opposed on the second dimen-sion. The first one contained more 2-heptanone (fruity,cinnamon) and hexanal (green, grass, and fat), which couldlead to its ‘‘Fatty’’ perception. 2,3-butanedione (butter),3-hydroxy-2-butanone (yoghurt, butter, and cream) and

Cocoa

Bread Bread

Vanilla Commercial bread

CakeButter

Bread

VanillaFoot

Bakerie odour

CocoaRoasted

SweetToasted bread

CaramelCocoa

CrumbAnise Crust

Flour

CaramelRoasted

Butter

Mild - Sweet

Fat oil

ButterCaramel

Brioche

Crumb

Flour Cardboard

Cardboard

Linseed oil

Wet grass

RuskHazelnut

AlcoholLinseed oil

Flour

FootDough

HazelnutFlour

PC 1 - 40.2%

PC 2

- 33

.2%

Attributes selection limit: absolute correlation value higher than 0,8

Fig. 5. Representation of the descriptive variables retained for the flash profile in the two first dimensions.

CAR/PDMS/DVB-

30 min - 35°C

CAR/PDMS-

30 min - 35°C

CAR/PDMS-

60 min - 35°C

CAR/PDMS/DVB-

60 min - 35°C

-6

-3

0

3

6

-7 -3.5 0 3.5 7PC 1 - 40.2%

PC 2

- 33

.2%

Fig. 6. Plot of the four HS-SPME extracts according to the odorant descriptors retained for the flash profile in the two first dimensions.

P. Poinot et al. / Food Research International 40 (2007) 1170–1184 1181

2-methylpropanol (alcohol, wine-like) were present inhigher amount in the second one. This could then explainits ‘‘Buttery’’ notes.

Thus, the flash profile revealed that even if volatilesamples were close to the same reference, they could becharacterised by sensory attributes more or less distinct.

2-Methyl-1-propanol

1-Propanol 2-Methylbutanal

3-Methyl-1-butanone

2,3-Butanedione 3-Hydroxy-2-butanone

2,3-Pentanedione

1-Ethoxy-2-propanol

Furfural

2-Acetylfuran

5-Methyl-2-furfural

2-Methylpyrazine

Butyric acid

Hexanal2-Heptanone

Pyrrole

Furfuryl alcohol

2-Pentylfuran

1-Hexanol

1-Pentanol

Ethanol

Acetic acid2,3-Butanediol

3-Methylbutanal

2-Methylpropanal

PC 1 - 65.4%

PC 2

- 22

.7%

Fig. 7. Correlation plot of the volatile compounds identified in the four HS-SPME representative extracts in the two first dimensions.

CAR/PDMS/DVB - 60 min - 35°C

CAR/PDMS - 60 min - 35°C

CAR/PDMS - 30 min - 35°C

CAR/PDMS/DVB - 30 min - 35°C

-4

-2

0

2

4

-6 -3 0 3 6PC 1 - 65.4%

PC 2

- 22

.7%

Fig. 8. Plot of the four HS-SPME representative extracts according to their qualitative composition in the two first dimensions.

1182 P. Poinot et al. / Food Research International 40 (2007) 1170–1184

This could be linked to little or important qualitative differ-ences which existed between them.

4. Conclusion

HS-SPME has been successfully applied to extractpartially baked bread volatile compounds. Among the 27different HS-SPME samples obtained, four were character-

ised by an odour really close to the bread one. Thus aCAR/PDMS or a CAR/PDMS/DVB fibre associated withan extraction time of 30 min or 60 min and an extractiontemperature of 35 �C allowed obtaining volatile extractsrepresentative of the bread odour. Completed by a recentdescriptive sensory analysis, the flash profile, these fourextracts could have been differentiated according to specificodorant descriptors. These sensory results could be

P. Poinot et al. / Food Research International 40 (2007) 1170–1184 1183

strongly linked to the extracts qualitative compositionwhich was also analysed.

The study of the representativeness of food extracts cou-pled with their descriptive analysis seems to be an interest-ing tool to optimise extraction techniques.

Statistical analysis

Data from the similarity and the intensity tests wereanalysed with Statgraphics Plus 5.1 Software (Manugistics,Rockville, Maryland, USA). Principal component analysis(PCA) was performed with Uniwin Plus 5.1 Software(Sigma Plus, Paris, France).

Acknowledgements

This study has been carried out with financial supportfrom the Commission of the European Communities, FP6,Thematic Area ‘‘Food Quality and Safety’’, FOOD-2006-36302 EU-FRESH BAKE. It does not necessarily reflectits views and in no way anticipates the Commission’s futurepolicy in this area. The technical assistance of Catherine Fil-lonneau, Michelle Moreau, Cecile Marzin and the ENI-TIAA technology hall staff are gratefully acknowledged.We also thank the panellists for their participation duringall the sensory sessions, and Vincent Varlet for his help.

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