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Searching the missed flavour: chemical and sensory characterisation of flavour compounds released during baking
W.L.P. Bredie and M.A. Petersen (Editors) Flavour Science: Recent Advances and Trends 9 2006 Elsevier B.V. All rights reserved.
605
Searching the missed flavour: chemical and sensory characterisation of flavour compounds released during baking Barbara Rega, Aur61ie Guerard, Murielle Maire and Pierre Giampaoli ENSIA- UMR Scale, 1 av. des Olympiades, Massy 91300, France
ABSTRACT An original 'on-line' system coupled with SPME (solid phase microextraction) and GCMS analysis was developed in order to extract and analyse aroma compounds released during baking. Four different SPME fibres were used in order to investigate their extraction efficiency and how well they represented the odour produced during baking. A similarity test showed that the global odour emerging from SPME extracts was close to that of the reference (the odour of the baking cake). The hedonic test on SPME extracts and gas-chromatography coupled to olfactometry allowed to identify key odorant zones related with the 'tasty' odour of cake baking. 1. I N T R O D U C T I O N The baking process of amylaceous products leads to the formation of numerous volatile compounds which determine the sensory quality of final products and increase consumer acceptance. One of the most important reactions taking place is the Maillard reaction which leads to the formation of coloured compounds as well as a large number of volatile aroma compounds like pyrazines which are responsible for typical nutty and crust odours [1]. Although the baking process causes flavour development, it is also responsible for a strong loss in pleasant aroma compounds which are released in steam during the thermal treatment. Concerning baked products, the typical flavour of bread, crackers, and cookies was largely studied [2,3], and a few studies have been made on flavours produced during extrusion cooking [4]. The aim of this study was to develop an on-line device to analyse aroma compounds released during the baking of a model sponge cake in order to gain knowledge in which volatile compound contributes to the pleasant odour diffusing out of the oven.
606 2. M A T E R I A L S A N D M E T H O D S
Ingredients and making procedure were established following the CANAL Arle Project protocol [5]. During cake baking, vapours were carried to a flask (flow = 170 cm3/s) containing the SPME fibre. SPME extraction of volatile compounds was performed dynamically in two ways: (i) during the whole time of baking (25 min) and (ii) at different baking intervals (5-10 min, 10-15 min, 15-20 min and 15-25 min). Four different SPME fibres were used: 100 btm PDMS, 65 btm PDMS/DVB, 75 Jam CAR/PDMS and Stableflex 50/30 btm DVB/CAR/PDMS (Supelco Bellfonte, PA). The extraction temperature was optimised to 15 ~ by preliminary tests. All samples were immediately analysed in triplicate by GC-MS. SPME fibres were desorbed into a Fisons gas chromatograph equipped with a Trio 1000 mass detector and a DB-Wax column (J&W Science, i.d. 0.32 ram, 30 m, film thickness of 0.5 lam). Mass spectral matches were determined by comparison with NIST (Gaithersburg, MD), ENSIA (France) and INRAMASS (INRA, France) mass spectra libraries. Linear Kovats' Indices of authentic compounds were used to confirm identifications. A similarity test was made using a direct olfactometry device according to Rega et al. [6] and working with eight trained panellists. In order to familiarise subjects with the odour of the sponge cake baking, they were allowed to memorise this odour during the cake making. The similarity test was performed in duplicate on the five samples presented in Latin square: four SPME extracts (25 min) and a sponge cake aroma. A dummy product (the sponge cake aroma) was always presented first. Sniffers were first asked to smell and memorise the reference (the sponge cake just taken out of the oven and put in a sealed box). Then they evaluated samples rating similarity to the reference using a 10 cm scale ranging from 0 to 10 (close to/far from the reference). ANOVA and Newman-Keuls test were performed on similarity rates (p<0.05). In order to find interesting aroma compounds released from the cake during baking, thirty eight panellists were asked to hedonically evaluate the SPME extracts obtained at different cooking times by the DVB/CAR/PDMS fibre, lso-intense extracts were obtained at 5-10 rain, 10-15 rain, 15-20 min and 15-25 rain of baking. The hedonic test was performed using direct olfactometry. Samples were presented in a Latin square. Panellists were asked to rank samples according to their preference and then to rate them using a 10 cm scale ranging from 0 (dislike) to 10 (like). They were also invited to give free semantic descriptions. Friedman test and Page test were performed on ranking, ANOVA and Newman-Keuls test were performed on hedonic rates (p<0.05). Gas chromatography-olfactometry analysis (GCO) was performed on the most pleasant fractions using experienced sniffers in order to identify volatiles involved in the 'tasty' odours of cake baking. Chromatographic conditions were the same as previously mentioned but the GC effluent was split 1:1 between the FID detector and the sniffing port (250 ~ For each odour stimulus, panellists recorded the detection time and gave a free semantic description.
607 3. R E S U L T S AND D I S C U S S I O N
The on-line device was able to efficiently extract a great number of volatile compounds, e.g. a large number of alcohols, heterocyclic compounds, aldehydes and ketones. Different SPME fibres led to very different chromatographic profiles. The DVB/CAR/PDMS fibre led to the highest number of extracted compounds, whereas the CAR/PDMS fibre allowed to extract very volatile compounds like the Strecker aldehyde 3-methylbutanal. The PDMS fibre was less effective. Table 1 shows that among the heterocyclic compounds extracted, a large number of mono- and dimethylpyrazines (which are known to be key odorants in bread crust) were identified as well as maltol and its precursor 2,3-dihydro-3,5-dihydroxy-6-methyl-4(H)-pyran-4-one. The similarity test showed that the odour of all total SPME extracts (25 min) were very close to that of the reference with similarity rates ranging from 3.8 to 4.3 despite the sponge cake aroma (7.7 and 8). Among SPME fibres, DVB/Car/PDMS gave the best similarity results (3.8), even though the Newman-Keuls test showed no significant differences among the SPME extracts. Table 1. Heterocyclic compounds extracted by on-line SPME. Identification 2-Pentylfuran Methylpyrazine 2,5-Dimethylpyrazine 2,6-Dimethylpyrazine 2,3-Dimethylpyrazine 2,3,5-Trimethy lpyrazine Acetylpyrazine Furfural 5-Hydroxymethylfurfural Maltol Furaneol 2,3-Dihy dro- 3,5-dihy droxy-6methyl-4(H)-pyran-4-one
t/I
DVB/Car/PDMS
Car/PDMS
PDMS
1215 1249 1305 1312 1329 1389 1605 1441 2461 2022 2066 2244
X X X X X X X X X X X X
X X X
X
X X X X X X X X
X X X X X
By means of the DVB/Car/PDMS fibre flavour compounds produced at different baking times (5-10 min, 10-15 min, 15-20 min and 15-25 min) were extracted. The direct olfactometry hedonic test showed that preference increased gradually with baking time (Page test significant at 5%, Table 2). The analysis of the free semantic descriptors contributed to explain hedonic results: the global odours of 10-15 min, 15-20 rain and 20-25 rain extracts are related to 'baking cake', 'sweet' and 'crust' descriptors (Figure 1) whereas the 'not tasty' descriptor was only used for the 5-10 rain extract.
608 Table 2. Preference rating and ranking test of the on-line SPME extracts during baking.
Preference rating Rank
5-10 min
10-15 min
15-20 min
20-25 min
4.08 2.89
4.68 2.47
5.03 2.28
5.16 2.36
Figure l. Sensory profile of SPME baking extraction. GC-Olfactometry was applied to a 15-25 rain baking extract. Six very interesting odour zones related with the 'tasty' flavour were identified. The main odour zone (relative to intensity and frequency o f detection) was related to 'praline', 'baking cake' and 'very pleasant' descriptors and it is most probably due to the presence o f acetylpyrazine. 4. C O N C L U S I O N The 'on-line' system coupled with SPME was able to extract volatile compounds released during the baking of a model cake. Instrumental as well as sensory analyses coupled with the direct olfactometry device allowed us to identify the vapour fraction mainly responsible for the 'tasty' odour released during the baking process. References
1. 2. 3. 4.
H. Maarse (ed.), Volatile compounds in foods and beverages, NY, USA (1991) 41. C. Prost, C.Y. Lee, P. Giampaoli and H. Richard, J. Food Sci., 58 (1993) 586. G. Zehentbauer and W. Grosch, J. Cereal Sci., 28 (1) (1998) 81. R.L. HeiniO, K. Katina, A. Wilhelmson, O. Myllym~iki, T. Rajamfiki, K. Latva-Kala, K.-H. Liukkonen and K. Poutanen, Lebensm. Wiss. Technol., 36 (2003) 533. 5. T. Hoffman, M. Rothe and P. Schieberle (eds.), State of the art in flavour chemistry and biology, proceedings of the 7th Wartburg symposium, Garching, Germany (2005) 408. 6. B. Rega, N. Fournier and E. Guichard, J. Agric. Food Chem., 51 (2003) 7092.
605
Searching the missed flavour: chemical and sensory characterisation of flavour compounds released during baking Barbara Rega, Aur61ie Guerard, Murielle Maire and Pierre Giampaoli ENSIA- UMR Scale, 1 av. des Olympiades, Massy 91300, France
ABSTRACT An original 'on-line' system coupled with SPME (solid phase microextraction) and GCMS analysis was developed in order to extract and analyse aroma compounds released during baking. Four different SPME fibres were used in order to investigate their extraction efficiency and how well they represented the odour produced during baking. A similarity test showed that the global odour emerging from SPME extracts was close to that of the reference (the odour of the baking cake). The hedonic test on SPME extracts and gas-chromatography coupled to olfactometry allowed to identify key odorant zones related with the 'tasty' odour of cake baking. 1. I N T R O D U C T I O N The baking process of amylaceous products leads to the formation of numerous volatile compounds which determine the sensory quality of final products and increase consumer acceptance. One of the most important reactions taking place is the Maillard reaction which leads to the formation of coloured compounds as well as a large number of volatile aroma compounds like pyrazines which are responsible for typical nutty and crust odours [1]. Although the baking process causes flavour development, it is also responsible for a strong loss in pleasant aroma compounds which are released in steam during the thermal treatment. Concerning baked products, the typical flavour of bread, crackers, and cookies was largely studied [2,3], and a few studies have been made on flavours produced during extrusion cooking [4]. The aim of this study was to develop an on-line device to analyse aroma compounds released during the baking of a model sponge cake in order to gain knowledge in which volatile compound contributes to the pleasant odour diffusing out of the oven.
606 2. M A T E R I A L S A N D M E T H O D S
Ingredients and making procedure were established following the CANAL Arle Project protocol [5]. During cake baking, vapours were carried to a flask (flow = 170 cm3/s) containing the SPME fibre. SPME extraction of volatile compounds was performed dynamically in two ways: (i) during the whole time of baking (25 min) and (ii) at different baking intervals (5-10 min, 10-15 min, 15-20 min and 15-25 min). Four different SPME fibres were used: 100 btm PDMS, 65 btm PDMS/DVB, 75 Jam CAR/PDMS and Stableflex 50/30 btm DVB/CAR/PDMS (Supelco Bellfonte, PA). The extraction temperature was optimised to 15 ~ by preliminary tests. All samples were immediately analysed in triplicate by GC-MS. SPME fibres were desorbed into a Fisons gas chromatograph equipped with a Trio 1000 mass detector and a DB-Wax column (J&W Science, i.d. 0.32 ram, 30 m, film thickness of 0.5 lam). Mass spectral matches were determined by comparison with NIST (Gaithersburg, MD), ENSIA (France) and INRAMASS (INRA, France) mass spectra libraries. Linear Kovats' Indices of authentic compounds were used to confirm identifications. A similarity test was made using a direct olfactometry device according to Rega et al. [6] and working with eight trained panellists. In order to familiarise subjects with the odour of the sponge cake baking, they were allowed to memorise this odour during the cake making. The similarity test was performed in duplicate on the five samples presented in Latin square: four SPME extracts (25 min) and a sponge cake aroma. A dummy product (the sponge cake aroma) was always presented first. Sniffers were first asked to smell and memorise the reference (the sponge cake just taken out of the oven and put in a sealed box). Then they evaluated samples rating similarity to the reference using a 10 cm scale ranging from 0 to 10 (close to/far from the reference). ANOVA and Newman-Keuls test were performed on similarity rates (p<0.05). In order to find interesting aroma compounds released from the cake during baking, thirty eight panellists were asked to hedonically evaluate the SPME extracts obtained at different cooking times by the DVB/CAR/PDMS fibre, lso-intense extracts were obtained at 5-10 rain, 10-15 rain, 15-20 min and 15-25 rain of baking. The hedonic test was performed using direct olfactometry. Samples were presented in a Latin square. Panellists were asked to rank samples according to their preference and then to rate them using a 10 cm scale ranging from 0 (dislike) to 10 (like). They were also invited to give free semantic descriptions. Friedman test and Page test were performed on ranking, ANOVA and Newman-Keuls test were performed on hedonic rates (p<0.05). Gas chromatography-olfactometry analysis (GCO) was performed on the most pleasant fractions using experienced sniffers in order to identify volatiles involved in the 'tasty' odours of cake baking. Chromatographic conditions were the same as previously mentioned but the GC effluent was split 1:1 between the FID detector and the sniffing port (250 ~ For each odour stimulus, panellists recorded the detection time and gave a free semantic description.
607 3. R E S U L T S AND D I S C U S S I O N
The on-line device was able to efficiently extract a great number of volatile compounds, e.g. a large number of alcohols, heterocyclic compounds, aldehydes and ketones. Different SPME fibres led to very different chromatographic profiles. The DVB/CAR/PDMS fibre led to the highest number of extracted compounds, whereas the CAR/PDMS fibre allowed to extract very volatile compounds like the Strecker aldehyde 3-methylbutanal. The PDMS fibre was less effective. Table 1 shows that among the heterocyclic compounds extracted, a large number of mono- and dimethylpyrazines (which are known to be key odorants in bread crust) were identified as well as maltol and its precursor 2,3-dihydro-3,5-dihydroxy-6-methyl-4(H)-pyran-4-one. The similarity test showed that the odour of all total SPME extracts (25 min) were very close to that of the reference with similarity rates ranging from 3.8 to 4.3 despite the sponge cake aroma (7.7 and 8). Among SPME fibres, DVB/Car/PDMS gave the best similarity results (3.8), even though the Newman-Keuls test showed no significant differences among the SPME extracts. Table 1. Heterocyclic compounds extracted by on-line SPME. Identification 2-Pentylfuran Methylpyrazine 2,5-Dimethylpyrazine 2,6-Dimethylpyrazine 2,3-Dimethylpyrazine 2,3,5-Trimethy lpyrazine Acetylpyrazine Furfural 5-Hydroxymethylfurfural Maltol Furaneol 2,3-Dihy dro- 3,5-dihy droxy-6methyl-4(H)-pyran-4-one
t/I
DVB/Car/PDMS
Car/PDMS
PDMS
1215 1249 1305 1312 1329 1389 1605 1441 2461 2022 2066 2244
X X X X X X X X X X X X
X X X
X
X X X X X X X X
X X X X X
By means of the DVB/Car/PDMS fibre flavour compounds produced at different baking times (5-10 min, 10-15 min, 15-20 min and 15-25 min) were extracted. The direct olfactometry hedonic test showed that preference increased gradually with baking time (Page test significant at 5%, Table 2). The analysis of the free semantic descriptors contributed to explain hedonic results: the global odours of 10-15 min, 15-20 rain and 20-25 rain extracts are related to 'baking cake', 'sweet' and 'crust' descriptors (Figure 1) whereas the 'not tasty' descriptor was only used for the 5-10 rain extract.
608 Table 2. Preference rating and ranking test of the on-line SPME extracts during baking.
Preference rating Rank
5-10 min
10-15 min
15-20 min
20-25 min
4.08 2.89
4.68 2.47
5.03 2.28
5.16 2.36
Figure l. Sensory profile of SPME baking extraction. GC-Olfactometry was applied to a 15-25 rain baking extract. Six very interesting odour zones related with the 'tasty' flavour were identified. The main odour zone (relative to intensity and frequency o f detection) was related to 'praline', 'baking cake' and 'very pleasant' descriptors and it is most probably due to the presence o f acetylpyrazine. 4. C O N C L U S I O N The 'on-line' system coupled with SPME was able to extract volatile compounds released during the baking of a model cake. Instrumental as well as sensory analyses coupled with the direct olfactometry device allowed us to identify the vapour fraction mainly responsible for the 'tasty' odour released during the baking process. References
1. 2. 3. 4.
H. Maarse (ed.), Volatile compounds in foods and beverages, NY, USA (1991) 41. C. Prost, C.Y. Lee, P. Giampaoli and H. Richard, J. Food Sci., 58 (1993) 586. G. Zehentbauer and W. Grosch, J. Cereal Sci., 28 (1) (1998) 81. R.L. HeiniO, K. Katina, A. Wilhelmson, O. Myllym~iki, T. Rajamfiki, K. Latva-Kala, K.-H. Liukkonen and K. Poutanen, Lebensm. Wiss. Technol., 36 (2003) 533. 5. T. Hoffman, M. Rothe and P. Schieberle (eds.), State of the art in flavour chemistry and biology, proceedings of the 7th Wartburg symposium, Garching, Germany (2005) 408. 6. B. Rega, N. Fournier and E. Guichard, J. Agric. Food Chem., 51 (2003) 7092.