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

Food Research International 40 (2007) 1170–1184 www.elsevier.com/locate/foodres

Optimisation of HS-SPME to study representativeness of partially baked bread odorant extracts Pauline Poinot a,1, Joe¨lle Grua-Priol a,2, Gae¨lle Arvisenet a,3, Ce´cile Rannou Michel Semenou b,5, Alain Le Bail a,6, Carole Prost a,* b

a,4

,

a ENITIAA, UMR GEPEA CNRS 6144, Rue de la Ge´raudie`re, 44322 Nantes Cedex 3, France ENITIAA, UMR INRA Sensome´trie et de Chimiome´trie, Rue de la Ge´raudie`re, 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 compounds. During this study, three HS-SPME parameters (extraction time, extraction temperature, SPME fibre) were optimised on volatile compounds extraction thanks to a representativeness analysis. Results displayed that a CAR/PDMS or a CAR/PDMS/DVB fibre associated 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 they were close to the same bread odour. Completed by the analysis of their qualitative composition, the study revealed that there were some analytical differences in odour perceptions. These differences may be linked to synergic effects caused by the presence of characteristic volatile 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 most consumed foods in the world, under different forms depending on cultural habits (Cayot, 2007; Pozo-Bayo´n, Guichard, & Cayot, 2006). Bread is considered as a traditional food for French population. Following consumers preferences, *

Corresponding author. Tel.: +33 2 51 78 55 17; fax: +33 2 51 78 55 20. E-mail addresses: [email protected] (P. Poinot), [email protected] (J. Grua-Priol), [email protected] (G. Arvisenet), [email protected] (C. Rannou), [email protected] (M. Semenou), [email protected] (A.L. Bail), [email protected] (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. 0963-9969/$ - see front matter  2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodres.2007.06.011

a lot of studies have been carried out in order to improve bread texture, odour, flavour and bread shelf life (Ba´rcenas, Haros, Benedito, & Rosell, 2003). Those studies result in new technologies which answer the increasing European demand and reduce the complexity of the bakery process. Within this context, partially baked frozen and partially baked non-frozen breads have been developed in order to offer consumers fresh bread at any time of the day (Ba´rcenas 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 products in term of innovation and feasibility (Carr et al., 2006). Indeed, these technologies permit to decrease wasted products by adjusting the production to the demand of consumers. In addition, ‘‘hot points’’ permit to save manufacturing space and to reduce the baking equipments needed to prepare the products before retailing (Carr et al., 2006). Partially baked breads offer a lot of convenience and are leading products in term of market share among frozen and

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non-frozen industrial breads. Partially bread making process differs from traditional baked making process. Therefore, differences in term of texture, taste, odour and flavour may be expected in comparison to breads produced with conventional bread making process (Quı´lez, Ruiz, & Romero, 2006). These organoleptic properties greatly participate to the consumers acceptance of breads. Thus the study and the process control of the partially baked bread has become an important stake for the baking industry. Flavour is one of the main factors which influences consumers choices (Pozo-Bayo´n et al., 2006). Bread aroma has been largely studied, and many methods have been developed to identify the compounds responsible for its flavour (Cayot, 2007; Pozo-Bayo´n et al., 2006). More than 540 volatile compounds have been reported in the complex volatile fraction of bread (Ruiz, Quı´lez, 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-Bayo´n et al., 2006; Seitz, Chung, & Rengarajan, 1998). However, only a small part of these compounds plays a significant role in the final bread aroma (Cayot, 2007; Pozo-Bayo´n et al., 2006). Scientists are now interested in investigating which of the volatile compounds participate to the overall odour. Developments of extraction methods and analytical techniques have then been carried out with the aim of identifying these volatile compounds. The oldest technique used for the extraction of bread volatile compounds was solvent extraction (Rychlik & Grosch, 1996; Schieberle & Grosch, 1994; Zehentbauer & Grosch, 1998a, 1998b). Distillation (Ruiz et al., 2003) and vacuum distillation were more rarely employed (Frasse et al., 1992). Bread volatile compounds which strongly contribute to its global flavour were then characterised by coupling headspace with olfactometric methods as Aroma Extract Dilution Analysis (AEDA) (Schieberle, 1995). Solid-phase microextraction (SPME) is a particularly useful alternative method compared with others which are more tedious or more expensive. SPME has become one of the preferred techniques in aroma analysis, offering solvent free, rapid sampling with low cost and ease preparation. It is sensitive, selective and compatible with low detection limits (Ho, Wan Aida, Maskat, & Osman, 2006). Placed in the sample headspace, SPME is a nondestructive and non-invasive method to evaluate volatile and semi-volatile compounds (Ruiz et al., 2003). HeadSpace SPME (HS-SPME) reproduces sniffing conditions (Costa Freitas, Parreira, & Vilas-Boas, 2001) and as it could be used under low extraction temperature, it provides a good estimation of the aroma profile as perceived by the human nose (Ho et al., 2006). Extraction of volatile compounds of a great number of foods was carried out using HS-SPME extraction: palm sugar (Arenga pinnata) (Ho et al., 2006), cheese (Mallia, Fernandez-Garcia, & Olivier Bosset, 2005; Pinho, Peres, & Ferreira, 2003), coffees (Costa Freitas et al., 2001), ham (Garcia-Esteban, Ansorena, Astiasarran, Martin, & Ruiz, 2004), olive oils

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(Cavalli, Fernandez, Lizzani-Cuvelier, & Loiseau, 2003), and wine (Baptista, Tavares, & Carvalho, 2001). Recently, the first extraction of partially baked frozen bread volatile compounds was performed using HS-SPME (Ruiz et al., 2003). Volatile compounds released from several samples of French partially baked baguettes after their extraction by HS-SPME were then analysed (Quı´lez et al., 2006). These studies permitted also to highlight the influence of different HS-SPME conditions on the bread volatile compounds trapping. To be reproducible and highly sensitive, HS-SPME extraction implies the control of many parameters, which could differ with the food matrix used. The most influential parameters are among others extraction temperature, equilibrium time, extraction time, fibre coating. Within this context, Ruiz et al. (2003) showed that a 75 lm CAR/PDMS (Carboxen/Polydimethylsiloxane) fibre, an extraction time of 60 min, a temperature of 50 C and a sample of 0.5 g in a 20 mL flask were, among the tested conditions, the ones which permitted to extract the greatest quantity of volatile compounds. If impacts of HS-SPME conditions on the quantitative and qualitative release of partially baked frozen bread volatile compounds have been studied, the influence of these compounds on the global odour of HS-SPME extracts has not been investigated. An extraction method must indeed produce extracts which have odorant characteristics as close as possible to those of the corresponding food (Sarrazin, Le Que´re´, Gretsch, & Liardon, 2000). Thus the study of volatile extracts representativeness by comparing their odour to the one of the corresponding food, could be an accurate tool in order to validate the extraction technique 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-SPME conditions (fibre type, extraction time and extraction temperature) which permit to obtain volatile extracts representative of the odour of the corresponding partially baked bread. The present work extends the use of a factorial design in order to evaluate the odour representativeness of 27 volatile extracts obtained with three different fibres, associated with three different extraction temperatures and three different extraction times. Completed by a flash profile, the sensory differences between the samples whose odours were estimated by a panel to be representative of the bread odour were determined (Dairou & Sieffermann, 2002; Delarue & Sieffermann, 2004). The analysis of the bread volatile compounds of all volatile extracts was also assessed to link their presence 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,

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octadecane and nonadecane which were from Sigma (Saint Louis, USA), hexane from Merck (Darmstadt, Germany), and pentadecane from Fluka (Steinheim, Germany). Ethanol was purchased from Vermapur (Fontenay-sous-Bois, France). Standards were also employed for compounds identification. They were from Aldrich (Steinheim, Germany), except 1-propanol, 2,3-butanediol and the 2-methylpropionic acid which were from Fluka (Buchs, Switzerland), 2,3-pentanedione from SAFC (Steinheim, Germany), and acetic acid from Panreac (Barcelona, Spain).

Table 1 The 27 HS-SPME conditions tested

2.2. Bread sample

100 100 100 100 100 100 100 100 100

Commercial partially baked bread was used to carry out the experiments. For each extraction condition, one half baguette was baked for 15 min and then cooled at room temperature for 30 min. It was then cut in slices and entirely crushed (crust and crumb). Six grams of crushed bread were weighed and placed in a 125 mL flask. A magnetic stirring bar was also added in the flask which was then sealed with a silicone septum. The flask was immersed in a water bath whose temperature was controlled. In order to evaluate the extraction temperature effect, three different temperatures were studied (Table 1). After 5 min equilibrium, each of the tested fibres (Table 1) was exposed to the sample headspace for one of the three extraction times (Table 1). Twenty-seven different extracts were then assessed. During the extraction process, sample was continuously shaken with the magnetic stirring bar. At the end of the extraction time, the fibre was inserted into a gas chromatograph (GC) injector port for thermal desorption of the extracted volatiles during 5 min. 2.3. GC-FID Extracts collection as well as volatile compounds quantification were performed with a Varian Star 3400 Gas Chromatograph, coupled to a flame ionisation detector (FID) and a sniffing port. Volatile compounds were separated 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 rate of 1 mL min 1 (pressure: 75.8 kPa). The injector was at 260 C in split 1:1 mode for 2 min. It was then put in splitless mode until the end of the run time. The oven temperature program was held for 2 min at 45 C, then increased by 5 C min 1 to 50 C, by 0.5 C min 1 to 51 C, by 8 C min 1 to 170 C, and then by 18 C min 1 to 230 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 was done in a 100 mL glass gas syringe (Hamilton Gastight 1000, Alltech, France) fitted with a valve (Mininert, All-

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

Extraction times (min)

Extraction temperature (C)

75 75 75 75 75 75 75 75 75

15 15 15 30 30 30 60 60 60

25 35 50 25 35 50 25 35 50

15 15 15 30 30 30 60 60 60

25 35 50 25 35 50 25 35 50

15 15 15 30 30 30 60 60 60

25 35 50 25 35 50 25 35 50

CAR/PDMS CAR/PDMS CAR/PDMS CAR/PDMS CAR/PDMS CAR/PDMS CAR/PDMS CAR/PDMS CAR/PDMS PDMS PDMS PDMS PDMS PDMS PDMS PDMS PDMS PDMS

50/30 50/30 50/30 50/30 50/30 50/30 50/30 50/30 50/30

CAR/PDMS/DVB CAR/PDMS/DVB CAR/PDMS/DVB CAR/PDMS/DVB CAR/PDMS/DVB CAR/PDMS/DVB CAR/PDMS/DVB CAR/PDMS/DVB CAR/PDMS/DVB

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

tech, France) and a Teflon end (Alltech, France). Before the injection of the extract in GC, a syringe was placed on a polyvalent syringe pump (VIT-FIT, Lambda, Switzerland) and connected to the sniffing port placed at the end of the GC column using a glass column connector (Universal Quick Seal, Varian, USA). Thanks to this device, half of the GC total flow (containing aroma compounds) was pulled to the FID detector, and the other half was pulled and collected in the syringe. 2.5. GC–MS analysis The identification and quantification of volatile compounds were carried out with a Gas Chromatograph Agilent 6890 N coupled to a quadrupole mass detector (MS) Agilent 5973 Network. The GC program was the same as described for GC-FID analysis. The injector temperature was set at 260 C and mass detector at 250 C. Volatile compounds were pulled by a helium carrier gas with a flow rate of 3 mL min 1 (pressure: 62.4 kPa). The mass detector operated in scan mode, with electronic impact ionization (ionization energy 70 eV), and a mass range of 33–300 amu and a scan rate of 2.72 scans s 1, used to detect the ions formed. Compounds identification was based on mass spectra identification (comparison with

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standard MS spectra databases: Wiley 6), and standards injections. 2.6. Sensory analysis 2.6.1. Similarity and intensity tests The panel was composed of nine judges (2 men and 7 women, aged from 25 to 50 years) from our research department. The panel has been previously trained during 10 sessions to the quantification of similarity and intensity between a bread reference and samples belonging to the product space. The panel was also used to smell a gaseous odorant extract from gas syringes. Two syringes were presented to the judges. The first one was the reference and contained partially baked bread. To be in iso-intensity by comparison with the HS-SPME volatile extracts, it contained 0.5 g of crushed partially baked bread. The other one was a volatile extract obtained under one of the HS-SPME conditions (Table 1). Judges were asked to smell 10 mL of the two gaseous samples and to assess their odour proximity on a 100 mm scale, anchored at the left end with ‘‘very different from the reference’’ and at the right end with ‘‘identical to the reference’’. They were also asked to quantify the odour intensity of the extract by comparison with the odour of the reference. A 100 mm scale anchored at the left end with ‘‘less intense than the reference’’, at the right end with ‘‘more intense than the reference’’, and at the middle with ‘‘identical to the reference’’ was used for extracts scoring. Before the analysis of the representativeness of these 27 different HS-SPME extracts, three of them were first presented to the panellists three times, except for one judge who appreciated one of these three samples two times. These three extracts corresponded to the association of a 100 lm PDMS fibre with 15 min and 25 C, and a 75 lm CAR/PDMS fibre with 30 min and 35 C and finally a 50/30 lm CAR/PDMS/DVB fibre with 60 min and 50 C. The aim of this study was to verify the panel discriminative capacity and its coherence. 2.6.2. Flash profile The descriptive evaluation of volatile extracts was performed thanks to a flash profile. This sensory analysis was performed in order to highlight odorant differences between the samples found to be the closest to the odour of the bread reference, according to the previous similarity and intensity tests. The panel dedicated to the flash profile was composed of nine judges (1 man and 8 women, aged from 25 to 50 years) recruited in our research department. They were all experienced in sensory descriptive analysis. The evaluation consisted in two individual sessions. A brief outline of the procedures was previously given to judges. During these two sessions, volatile extracts were presented in gas syringes, obtained after their corresponding extraction.

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During the first session, the gaseous samples were presented simultaneously. After having smelt them, they were asked to generate odorant attributes sufficiently different to allow a ranking of the samples. No limitation was given regarding the number of sensory characteristics they could give. They were not allowed to generate hedonic terms. All the sensory characteristics generated by the whole panel were gathered in a single list. At the beginning of the second session, panellists were asked to read this list and to adapt their own list if they wished. The assessors were then presented all the samples simultaneously and they had to rank them along the sensory attributes belonging 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. For the two sessions, judges could smell the samples as much as they wanted and could take time they needed to evaluate them. 2.7. Statistical analysis Judges performance was first verified thanks to an analysis of variance (ANOVA) on the odour similarity and intensity scores given to the three repeated samples. The same statistical test was carried out on scores given to the 27 samples to identify if there was a sample effect on odour similarity and intensity, and then to determine the effects of the three factors (SPME fibre, extraction time and extraction temperature) and their interactions. Possible significant differences between the mean scores obtained for each sample were evaluated by least significant differences (LSD) multiple comparison tests with a confidence level of 95%. PCA was applied to the data from flash profile to assess the semantic interpretation and to characterise samples differences. Only attributes characterised by a correlation distance to the sensory map superior to 0.8 were used to describe the samples. A PCA was also performed on the relative area counts obtained for each aromatic extract. This final step allowed us 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 thanks to the three repeated samples. Results are presented first on the odour similarity (Table 2), and then on the odour intensity (Table 3). The ANOVA showed that judges were able to discriminate different samples in terms of odour similarity and odour intensity at a confidence level of 95% (Tables 2 and 3). Indeed, for both similarity and intensity tests, P-values corresponding to the samples effects were below

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

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

Source

Sum of squares

Sensory test Main effects

Df

Odour similarity P-value

Odour intensity P-value

Main effects A: Judges B: Samples

105.657 451.596

8 2

A: Judges B: Samples

8 26

0.0000 0.0000

0.0000 0.0000

70.5764 166.345 797.375

16 53 79

Interactions AB Residual Total (corrected)

Df

Mean square

Fratio

Pvalue

13.2071 225.798

4.21 71.94

0.0006 0.0000

1.41

0.1753

4.41103 3.13858

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

Table 3 Multiway ANOVA on odour intensity scores given to the three repeated samples Source

Sum of squares

Main effects A: Judges B: Samples

31.2528 225.414 31.3828 72.4317 362.327

Interactions AB Residual Total (corrected)

Df

Mean square

Fratio

Pvalue

8 2

3.90659 112.107

2.86 82.47

0.0102 0.0000

16 53 79

1.96142 1.36664

1.44

0.1615

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

5%. The results reported in Tables 2 and 3 also demonstrate that there were judge’s effects on odour similarity and odour intensity scores while there was no interaction between ‘‘judges · samples’’ factors. An absence of a significant interaction between these two factors revealed that judge’s effects were only due to a different use of scale by the panellists. Indeed, some of them could score the samples on the overall length of the scale, while others only used a little part of the scale. It was also possible that some of them tended to score the samples on the right part of the scale, whereas others were inclined to give low notes to all the samples. This could be linked to judge’s subjectivity concerning their similarity judgement. Thus there was a consensus between panellists, and they perceived in the same way the odour similarity and the odour intensity of the different extracts. 3.1.2. Extracts representativeness Twenty-seven different extracts were presented to the panel who was asked to quantify the odour similarity and intensity between each extract and the bread reference on two 100 mm scales. ANOVA and LSD tests on judge’s scores given to the 27 extracts according to their odour similarity and their odour intensity were first performed (Table 4). The samples effect and the judges effect were thus studied. The results showed that there was a samples effect at a significant level of 5%.

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

Thus, the odour and the intensity of the 27 extracts presented were different from one another. It could then be assumed that different HS-SPME conditions led to samples more or less close to the initial product, either in odour similarity or in odour intensity. As it was demonstrated before, the judge’s effect was only due to the different use of scales by the panellists. The effect of the three SPME parameters tested (fibre type, extraction time and extraction temperature) on the odour extract representativeness were then assessed (Tables 5 and 6). The fibre type and the extraction time influenced the odour similarity and the odour intensity of the extracted samples. Seventy-five micrometer CAR/PDMS and 30/ 50 lm CAR/PDMS/DVB fibres allowed obtaining volatile extracts close to the odour of the bread reference in terms of odour similarity and odour intensity. This could be due to the trapping sensitivity of these two fibres in regard to the one of the 100 lm PDMS. Indeed the 100 lm PDMS preferentially traps non-polar compounds (Bicchi et al., 2005; Bicchi, Cordero, & Rubiolo, 2004; Guerrero, Marin, Mejias, & Barroso, 2006; Tienpont, David, Bicchi, & Sandra, 2000; Zuin et al., 2006), while the two others are composed of polymeric multiphases which permit them to trap non-polar and polar compounds. The different nature of their phases could then explain the low quantity of bread volatile compounds trapped on the 100 lm PDMS fibre and thus a low intensity and a low representativeness of the corresponding extracts. The extraction time effect revealed that extracts obtained for 30 or 60 min extraction time were characterised by an odour and intensity closer to the reference one. Thus, an extraction time of 15 min was not sufficient to trap bread volatile compounds. Table 5 Multiway ANOVA of HS-SPME conditions effects on odour similarity and odour intensity scores Sensory test Effects

Odour similarity P-value

Odour intensity P-value

A: Fibres B: Extraction time C: Extraction temperature AB AC BC

0.0000 0.0001 0.0007 0.2353 0.0986 0.0045

0.0000 0.0000 0.0544 0.0079 0.0175 0.0909

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

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Table 6 Graphs 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.

The extraction temperature had only a significant effect on the odour similarity. An extraction temperature of 25 C did not allow obtaining volatile extracts similar to the bread odour reference. An explanation of this effect could be the absence of volatilisation of heavy molecular compounds when low temperature was applied. Thus only a small part of bread volatile compounds were trapped on SPME fibres. An extraction temperature of 35 C permitted to obtain volatile extracts which were representative of the bread odour reference. A higher temperature of 50 C allowed obtaining extracts which were as intensive as the reference but characterised by an odour different from the bread one. The formation and the release of additional compounds under this temperature, like Maillard volatile compounds, could explain the low representativeness of the corresponding extracts. A significant interaction between the extraction time factor and the extraction temperature factor occurred for the odour similarity (Tables 5 and 7). This interaction revealed that volatile extracts were significantly closer to the bread odour reference when a temperature of 35 C was associated to a time of 30 min whatever the fibre type was.

Odour intensity was influenced by an interaction between the fibre factor and the extraction time factor, as well as between the fibre factor and the extraction temperature factor. The first interaction indicated that a 75 lm CAR/PDMS fibre associated with an extraction time of 30 min or 60 min led to volatile extracts closer to the reference in terms of intensity. The same results were obtained with a 50/30 lm CAR/PDMS/DVB fibre. The second interaction revealed that a 75 lm CAR/PDMS or a 50/ 30 lm CAR/PDMS/DVB fibre associated with an extraction temperature of 35 C or 50 C permitted to obtain volatile extracts which were characterised by higher intensity. The LSD test which was realised after the one-way ANOVA performed on the means judge’s scores obtained for each sample, permitted to differentiate and rank the 27 volatile samples according to their odour similarity to the bread reference (Fig. 1). The same study was undertaken on their odour intensity proximity (Fig. 2). The results shown in Fig. 1 illustrated the previous ANOVA analysis. Indeed, four extracts had odorant characteristics close to the ones of the bread reference and belonged to the first LSD group. These extracts were

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Interaction

Odour similarity

Odour intensity

AB: Fibre/time

No significant effect

Odour intensity scores

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

Time 15 min 30 min 60 min

4.3 3.8 3.3 2.8 2.3 1.8 1.3

CAR/PDMS PDMS CAR/PDMS/DVB

Odour intensity scores

Fibre

No significant effect

Odour similarity scores

AC: Fibre/temperature

BC: Time/temperature

3.6 3.1 2.6 2.1 1.6 1.1 CAR/PDMS PDMS CAR/PDMS/DVB

Fibre

Fibre

7.1

Temperature 25°C 35°C 50°C

4.1

No significant effect

Temterature 25°C 35°C 50°C

6.1 5.1 4.1 3.1 15 min

30 min

60 min

Time

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

Odour similarity Identical to the reference 10

9 8 7

Scores

6 5 4 3 2 1

PDMS -1 5min - 50°C

PDMS - 60min - 50°C

PDMS - 15min - 35°C

PDMS - 15min - 25°C

PDMS - 30min - 25°C

PDMS - 60min - 35°C

PDMS - 60min - 25°C

PDMS - 30min - 50°C

CAR/PDMS - 15min - 50°C

CAR/PDMS/DVB - 15min - 25°C

CAR/PDMS - 30min - 25°C

CAR/PDMS - 15min - 35°C

CAR/PDMS/DVB - 30min - 25°C

CAR/PDMS/DVB - 15min - 35°C

PDMS - 30min - 35°C

CAR/PDMS - 30min - 50°C

CAR/PDMS/DVB - 60min - 25°C

CAR/PDMS/DVB - 15min - 50°C

CAR/PDMS/DVB - 60min - 50°C

CAR/PDMS - 15min - 25°C

CAR/PDMS/DVB - 30min - 50°C

CAR/PDMS - 60min - 25°C

CAR/PDMS - 60min - 50°C

CAR/PDMS/DVB - 60min - 35°C

CAR/PDMS - 60min - 35°C

CAR/PDMS/DVB - 30min - 35°C

CAR/PDMS - 30min - 35°C

Very different from the reference 0

Extracts 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 which belonged to the first LSD group at a confidence level of 95%.

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Odour intensity

More intense than the 10 reference 9 8 7

Scores

6

Identical to the reference

5 4 3

PDMS - 60min - 50°C

PDMS - 15min - 50°C

PDMS - 60min - 35°C

PDMS - 30min - 35°C

PDMS - 15min - 25°C

PDMS - 30min - 50°C

CAR/PDMS - 15min - 25°C

CAR/PDMS - 15min - 50°C

CAR/PDMS/DVB - 15min - 25°C

PDMS - 60min - 25°C

CAR/PDMS/DVB - 15min - 35°C

CAR/PDMS/DVB - 30min - 25°C

PDMS - 30min - 25°C

PDMS - 15min - 35°C

CAR/PDMS/DVB - 60min - 25°C

CAR/PDMS/DVB - 15min - 50°C

CAR/PDMS - 60min - 25°C

CAR/PDMS - 30min - 50°C

CAR/PDMS - 15min - 35°C

CAR/PDMS/DVB - 30min - 35°C

CAR/PDMS/DVB - 30min - 50°C

CAR/PDMS/DVB - 60min - 35°C

CAR/PDMS - 60min - 35°C

CAR/PDMS - 30min - 35°C

CAR/PDMS - 30min - 25°C

CAR/PDMS/DVB - 60min - 50°C

1 Less intense than the 0 reference

CAR/PDMS - 60min - 50°C

2

Extracts 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 which belonged to the first LSD group at a confidence level of 95%.

obtained with a 75 lm CAR/PDMS fibre associated with an extraction temperature of 35 C and an extraction time of 30 min or 60 min (noted CAR/PDMS-30 min-35 C and CAR/PDMS-60 min-35 C). In the same way, a 30/50 lm CAR/PDMS/DVB fibre, associated with an extraction time of 30 min or 60 min, and an extraction temperature of 35 C led to extracts which were close to the odour of the bread reference (noted CAR/PDMS/DVB-30 min35 C and CAR/PDMS/DVB-60 min-35 C). Moreover, it could be seen in Fig. 1 that extracts obtained for 30 min were closer from the reference than the two ones obtained with an extraction time of 60 min. According to Fig. 2, the extracts which had an odour intensity close to the odour intensity of the bread reference also corresponded to the HS-SPME conditions determined after the ANOVA analysis (Tables 5–7). Six HS-SPME extracts had an odour intensity close to the reference and belonged to the first LSD group. Within the first LSD group obtained for the odour intensity test, three extracts were also determined to have an odour similarity close to the bread reference. CAR/ PDMS-30 min-35 C and CAR/PDMS-60 min-35 C volatile extracts were, indeed, representative of the odour of bread. CAR/PDMS/DVB-60 min-35 C also led to extracts which were close to the bread odour reference in terms of odour similarity and odour intensity. Even if the intensity of the CAR/PDMS/DVB-30 min-35 C sample was a little less intense than the one of the three extracts cited before

(this extracts belonged to the second group of the intensity LSD test), it could also be considered to be representative of the bread odour because of its high score obtained for the odour similarity test. Thus, four different SPME conditions led to volatile extracts which were representative of the bread odour reference in terms of odour similarity and odour intensity. The study of the qualitative composition of the 27 samples was then undertaken in order to explain their different odorant perceptions. It consisted in identifying volatile compounds present in the samples as well as in quantifying their relative amount. Volatile compounds identified in the 27 extracts are presented in Table 8. A PCA was then performed on the relative area counts of volatile compounds identified under each condition. We noted a good inertia of PCA formed by the two first axes which explained 70.8% of total information. Each dimension was correlated with different bread volatile compounds. The correlation plot (Fig. 3) showed that the first axis opposed ethanol to the other compounds, especially to 2-ethoxy-1-propanol, 2-methylpyrazine, furfural, butyric acid, dihydro-2-methyl-3(2H)-furanone, 2,3-pentanedione, 5-methyl-2-furfural, hexanal and pyrrole. The second dimension was negatively correlated with 2-methylpropanal, 3-methylbutanal, 1-propanol, and 2-methyl-1-propanol (Fig. 3). Fig. 4 shows the representation of the 27 extracts on this bidimensional plot. This plot displays that extracts

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

Volatile compounds

Odorant attributes

78-84-2 96-17-3 590-86-3 64-17-5 431-03-8 71-23-8 600-14-6 66-25-1 78-83-1 1569-02-4 111-13-7 123-51-3 3777-69-3 71-41-0 109-08-0 513-86-0 3188-00-9

Maltyb,c Maltyb,c Maltyb,c,d Alcoholica Buttera,b,c,d Alcoholica Butterb,c Greenb,c,d, grassa, fata Alcoholica, wine likea

111-27-3

2-Methylpropanal 2-Methylbutanal 3-Methylbutanal Ethanol 2,3-Butanedione 1-Propanol 2,3-Pentanedione Hexanal 2-Methylpropanol 1-Ethoxy-2-propanol 2-Heptanone 3-Methyl-1-butanol 2-Pentylfuran 1-Pentanol 2-Methylpyrazine 3-Hydroxy-2-butanone Dihydro-2-methyl-3(2H)furanone 1-Hexanol

64-19-7

Acetic acid

98-01-1 109-97-7 1192-62-7 513-85-9 620-02-0 107-92-6 98-00-0

Furfural Pyrrole 2-Acetylfuran 2,3-Butanediol 5-Methyl-2-furfural Butyric acid Furfuryl alcohol

a b c d

Fruitya, cinnamona Maltyb,d alcoholicb,d Fruitya Fusel-like sweeta Burnta, sweeta Buttera, yoghurta, creama Rancida, buttera Grassa, woodya, milda, sweeta Acida,b, pungenta,b, sour a,b Burnta Burnta, sweeta Smokyb, roastyd Bitterb,c, almondb,c, sweeta Rancida,b, sweatyb Milda, warm oilya, burnta

Fenaroli (2002). Pozo-Bayo´n et al. (2006). Rychlik and Grosch (1996). Schieberle and Grosch (1994).

obtained with a 100 lm PDMS fibre were characterised by a higher quantity of ethanol and a lesser extent of the other compounds (dot circle). This result could be explained by two facts. One explanation could refer to the abundance of ethanol in the initial bread samples. Thus, despite its polar nature, ethanol was trapped in high quantity on this fibre. The second reason could be the low affinity of the other bread volatile compounds for this fibre. As a result, except ethanol, little amounts of volatile compounds were trapped on it, which may explain the low similarity and intensity scores given to these samples. 30/50 lm CAR/PDMS/DVB fibre permitted to extract higher quantity of Maillard volatile compounds than 75 lm CAR/PDMS and 100 lm PDMS fibres. These results 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 fibre allowed to extract Maillard compounds in high amounts. The formation and the release of such volatile compounds occurred under high temperature (50 C) or/and long time (60 min). Thus, under these conditions, Maillard reaction may happen in bread samples, leading to the formation

of furfural and furan derivatives which result in a loss of bread samples water (Pozo-Bayo´n et al., 2006). The results also revealed that for three of the four HSSPME conditions determined to be representative of the bread odour, the corresponding extracts had a close qualitative composition. Moreover, their composition differed from the one of the other extracts. These extracts corresponded to CAR/PDMS-30 min-35 C, CAR/PDMS60 min-35 C and CAR/PDMS/DVB-30 min-35 C. It could then be suggested that a representative odorant extract was characterised by a particular qualitative composition, which was only obtained under these three extraction conditions (continuous line). The three extracts were essentially represented on the second dimension. Their contribution to its global inertia was, respectively of 11.1% for CAR/PDMS-30 min-35 C, of 9% for CAR/PDMS60 min-35 C and 4.5% for CAR/PDMS/DVB-30 min35 C. These extracts were characterised by higher relative amounts of 2-methylpropanal, 3-methylbutanal, 1-propanol, and 2-methyl-1-propanol (Figs. 3 and 4). It could also be mentioned that they tended to contain 3-methyl-1-butanol, 2-methylpropanol, 2-methylbutanal, 3-hydroxy-2butanone and 2,3-butanedione in a relative high amount, while they were composed of medium quantity of ethanol. 2-methylbutanal, 3-methylbutanal, and 2-methylpropanal are Strecker aldehydes and they are characterised by a malty odour (Table 8). Associated with buttery and alcoholic notes, given by 2,3-butanedione and 3-hydroxy2-butanone on one hand, and by the 1-propanol and 2-methylpropanol on the other hand, they may conduct to a mix characterised by a bread odour. Nevertheless, it must not be forgotten that an odour is a result of interactions between volatile compounds. Thus high quantities of these volatile compounds in volatile extracts were not the only reasons to their bread odour. Indeed, these volatiles compounds interacted with others which were present in lower concentrations. It was the resulted mix which conducted to a bread odour. The last extract determined to be representative of the bread odour was not characterised by the same qualitative composition. Indeed CAR/PDMS/DVB-60 min35 C extract was essentially correlated with the first dimension (Fig. 4). Its inertia contribution was of 13%. Thus, this extract was composed of lower quantity of ethanol than the other samples, and higher relative quantity of furan derivatives (dihydro-2-methyl-3(2H)-furanone, 5-methyl-2-furfural and furfural) and pyrrole, butyric acid, 2-ethoxy-1-propanol, 2-methylpyrazine, hexanal, and 2,3-pentanedione. It may also be assumed that a bread odour could be obtained when Maillard compounds as furan derivatives, 2-methylpyrazine and pyrrole which are characterised by burnt and sweet notes are present in high relative quantity with fatty and green notes given by 2,3-pentanedione, hexanal, and butyric acid compounds (Table 8). To conclude, four volatile extracts were then found to be close to the bread odour. According to the study of their

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

Acetic acid

1179

1-Hexanol

PC 2 - 19.5%

1-Pentanol 2,3-Butanediol

2-Pentylfuran

Pyrrole Furfuryl alcohol 2-Heptanone Hexanal Butyric acid 2-Methylpyrazine 5-Methyl-2-furfural Furfural

Ethanol

2-Acetylfuran

1-Ethoxy-2propanol

Dihydro-2-methyl3(2H)-furanone 2,3-Pentanedione 3-Hydroxy-2butanone 2,3-Butanedione 3-Methyl-1-butanone 2-Methylbutanal 2-Methyl-1-propanol

1-Propanol

3-Methylbutanal 2-Methylpropanal

PC 1 - 51.3% Fig. 3. Correlation plot of qualitative data obtained for the 27 HS-SPME extracts in the two first dimensions.

4 CAR/PDMS/DVB- 60 min - 50°C CAR/PDMS/DVB- 60 min - 35°C PDMS- 60 min - 50°C PDMS- 30 min - 50°C CAR/PDMS/DVB- 15 min - 50°C

PDMS- 30 min - 35°C

2

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

CP 2 - 19.5%

PDMS- 15 min - 50°C

CAR/PDMS/DVB- 30 min - 50°C

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

PDMS- 30 min - 25°C

0 CAR/PDMS/DVB- 15 min - 35°C CAR/PDMS- 15 min - 25°

CAR/PDMS- 30 min - 50°C

CAR/PDMS- 15 min - 35°C CAR/PDMS/DVB- 60 min - 25°C

CAR/PDMS- 60 min - 50°C

CAR/PDMS- 15 min - 50°C CAR/PDMS- 30 min - 25°C

-2

CAR/PDMS/DVB- 30 min - 25°C CAR/PDMS- 60 min - 25°C CAR/PDMS/DVB- 30 min - 35°C CAR/PDMS/DVB- 15 min - 25°C CAR/PDMS- 60 min - 35°C CAR/PDMS- 30 min - 35°C

-4 -5

-2

1

4

7

CP 1 - 51.3% 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 bread odour.

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qualitative composition, three of these four extracts were characterised by a quite similar qualitative composition based on higher amounts of certain Strecker aldehydes, 2,3-butanedione, 1-propanol, and 2-methylpropanol. The other HS-SPME conditions led to a different qualitative composition, characterised by a lower quantity of ethanol, and higher quantities of Maillard furan derivatives (furfuryl alcohol and 2-pentylfuran), pyrrole and hexanal. While these extracts were close to the bread odour, their different qualitative composition could result in different consumers flavour perceptions. To analyse these sensory differences more precisely, a flash profile was conducted on these four extracts.

3.2. Flash profile A flash profile was performed in order to get some insights of the four optimum bread extracts flavour perceptions. 32 attributes were generated by the panel (Table 9). A PCA was performed to characterise the four extracts according to the odorant descriptors generated by all the panellists. Fig. 5 displays the configuration obtained by PCA. The examination of the correlation plot indicates

Table 9 Odorant attributes mentioned by the flash profile panel Individual attributes

Number of quotations

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

1 1 2 4 1 1 3 4 3 1 1 1 5 2 4 1 1 2 1 2 2 1 1 4 1 1 1 1 5 1 1 1 2

that the two first principal dimensions explained 73.4% of the total variance. Because of a different number of terms generated by each judge, and because of the difficulty to interpret them, only the attributes with an absolute correlation value higher than 0.8 were retained for the interpretation of the two first axes. According to this correlation plot, the first dimension was essentially positively associated with ‘‘Roasted’’, ‘‘Caramel’’ and ‘‘Cocoa’’ attributes. It was negatively correlated with 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 characterised by several attributes groups. They were distinctly placed in each quarter of the product plot. According to its right bottom position, CAR/PDMS-30 min-35 C sample 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 the left top quarter, was perceived to have both ‘‘Bread’’, ‘‘Fatty’’ and ‘‘Sweet bakeries’’ notes. CAR/PDMS60 min-35 C extract tended to have ‘‘Bread’’, ‘‘Cake’’ and ‘‘Buttery’’ notes. Finally, CAR/PDMS/DVB-60 min35 C sample was essentially characterised by ‘‘Green’’, ‘‘Fresh’’ and ‘‘Oily’’ attributes. It could be noticed that CAR/PDMS-30 min-35 C, CAR/PDMS-60 min-35 C and CAR/PDMS/DVB-30 min-35 C samples were all characterised by close attributes which could be gathered under ‘‘Bread’’ and ‘‘Sweety’’ notes. This could be due to their qualitative compositions which are quite similar (Figs. 3 and 4). Nevertheless, as these samples were characterised by different sensory descriptors by the panellists, it could be thought that little qualitative differences existed between them. This is shown on Figs. 7 and 8 which display the qualitative composition of the four representative extracts after a PCA. The two first principal dimensions accounted for about 88% of the total variance. It could be seen that CAR/PDMS-30 min-35 C sample was composed of higher quantities of ethanol (alcohol), 3-methylbutanal (malty) and 2-methylpropanal (malty) than the three others. It could then be supposed that higher amount of these three components could lead to a bread odour containing also ‘‘Roasted’’, ‘‘Caramel’’ and ‘‘Cocoa’’ attributes. Following the first dimension, this extract was opposed to the CAR/PDMS/DVB-60 min35 C extract. As it was shown in Fig. 4, its qualitative composition was really different from the others. This could be the result of its odorant specificity which was characterised by ‘‘Green’’, ‘‘Fresh’’ and ‘‘Oily’’ notes. CAR/PDMS-60 min-35 C and CAR/PDMS/DVB30 min-35 C samples were opposed on the second dimension. The first one contained more 2-heptanone (fruity, cinnamon) and hexanal (green, grass, and fat), which could lead to its ‘‘Fatty’’ perception. 2,3-butanedione (butter), 3-hydroxy-2-butanone (yoghurt, butter, and cream) and

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

Bread

Bread Vanilla

Fat oil

Brioche

Crumb

PC 2 - 33.2%

Flour

1181

Cocoa

Commercial bread Cake

Butter

Butter Caramel

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

Bread

Cardboard Vanilla Foot Bakerie odour Cocoa Roasted Sweet Caramel Cocoa Toasted bread Crumb Flour Anise Crust Caramel Roasted

Cardboard

Linseed oil

Wet grass Rusk Alcohol Hazelnut Linseed oil

Butter Mild - Sweet

Flour Dough F oot

Flour Hazelnut

PC 1 - 40.2% Fig. 5. Representation of the descriptive variables retained for the flash profile in the two first dimensions.

6 CAR/PDMS/DVB30 min - 35°C CAR/PDMS60 min - 35°C

PC 2 - 33.2%

3

0

-3 CAR/PDMS30 min - 35°C CAR/PDMS/DVB60 min - 35°C

-6 -7

-3.5

0

3.5

7

PC 1 - 40.2% Fig. 6. Plot of the four HS-SPME extracts according to the odorant descriptors retained for the flash profile in the two first dimensions.

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

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

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1-Ethoxy-2propanol

Ethanol

Hexanal

2-Heptanone

2-Pentylfuran

PC 2 - 22.7%

1-Pentanol

1-Hexanol 1-Propanol

2-Methylbutanal Butyric acid Pyrrole 2-Methylpyrazine 2,3-Butanediol Acetic acid Furfuryl alcohol Furfural 5-Methyl-2-furfural

3-Methylbutanal

2-Methylpropanal

2-Acetylfuran

2-Methyl-1-propanol

3-Methyl-1-butanone 2,3-Pentanedione 2,3-Butanedione

3-Hydroxy-2butanone

PC 1 - 65.4% Fig. 7. Correlation plot of the volatile compounds identified in the four HS-SPME representative extracts in the two first dimensions.

4 CAR/PDMS/DVB 30 min - 35°C

PC 2 - 22.7%

2 CAR/PDMS 30 min - 35°C

0 CAR/PDMS/DVB 60 min - 35°C

-2 CAR/PDMS 60 min - 35°C

-4 -6

-3

0

3

6

PC 1 - 65.4% Fig. 8. Plot of the four HS-SPME representative extracts according to their qualitative composition in the two first dimensions.

This could be linked to little or important qualitative differences which existed between them. 4. Conclusion HS-SPME has been successfully applied to extract partially baked bread volatile compounds. Among the 27 different HS-SPME samples obtained, four were character-

ised by an odour really close to the bread one. Thus a CAR/PDMS or a CAR/PDMS/DVB fibre associated with an extraction time of 30 min or 60 min and an extraction temperature of 35 C allowed obtaining volatile extracts representative of the bread odour. Completed by a recent descriptive sensory analysis, the flash profile, these four extracts could have been differentiated according to specific odorant descriptors. These sensory results could be

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

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