On-line dynamic HS-SPME for monitoring endogenous aroma compounds released during the baking of a model cake Barbara Rega * , Aurélie Guerard, Julien Delarue, Muriel Maire, Pierre Giampaoli AgroParisTech-UMR 1121 SCALE-1, av. Des Olympiades, 91744 Massy, France article info Article history: Received 9 November 2007 Received in revised form 6 March 2008 Accepted 8 May 2008 Keywords: Thermal process Volatile compounds Maillard reaction Lipid oxidation Sponge cake Dynamic SPME GC–Olfactometry Direct-GC–Olfactometry Sensory analysis abstract This work shows that using a dynamic SPME device combined with an instrumented oven, it is possible to monitor the release of a large amount of volatile compounds generated during the baking process of a real cereal product (sponge cake model) by directly sampling its baking vapours. The steam assisted dynamic SPME device made it possible to extract volatile compounds with very different volatility and hydropho- bicity, such as 5-hydroxymethylfurfural and 2-methyl-propanal. Time dependent analyses of baking vapours made it possible to simultaneously follow the release of several odour compounds and thermal reaction markers at different stages of their generation in the sponge cake model. The release of newly formed aroma compounds during baking significantly affected the odour quality of baking extracts as shown by odour profiles and sensory preferences evaluated by Direct-GC–Olfactometry. GC–Olfactome- try analysis was carried out on the final baking fractions to gain an understanding of the compounds which could contribute to overall odour quality. Ó 2008 Published by Elsevier Ltd. 1. Introduction During a thermal process such as baking, food products undergo intense transformation due to heat and mass transfer. Such changes are also partially governed by the initial composition of food ingredients which constitute the medium of the reactions (Chevalier, Colonna, Valle, & Lourdin, 2000). The baking of cereal products leads to a huge quantity of newly formed volatile com- pounds which play a major role in developing the flavour of the fi- nal product. These compounds are mainly the result of the Maillard reaction which occurs between reducing sugars and the -NH 2 func- tion of amino acids, peptides and proteins (Baltes, 1982). However, depending on raw material composition and processes, the Mail- lard reaction is not necessarily the only thermal reaction occurring during baking. In fact, both caramelisation and lipid oxidation can also take place. These reactions are known to be involved in the generation of odour active compounds such as aliphatic aldehydes and furfurals (Grosch & Schieberle, 1997; Kroh, 1994; Whitfield, 1992). Over the past few years numerous studies have dealt with the identification and quantification of the molecular compounds which have an impact on the flavour of the most common cereal products such as bread (Schieberle & Grosch, 1985; Schieberle & Grosch, 1992), the French baguette (Zehentbauer & Grosch, 1998), and cookies (Prost, Lee, Giampaoli, & Richard, 1993). The goal of such work has been to gain a deeper understanding of the role played by fermentation, enzyme activity and food components such as sugars and fat. Pozo-Bayon, Ruiz-Rodriguez, Pernin, and Cayot, (2007) recently showed that changing the formula of a sponge cake by substituting eggs with a leavening agent, produced important changes in some key aroma compounds such as meth- ional. Few interesting studies have been made on the impact of specific thermal processes, such as extrusion, on the generation of flavour compounds and its sensory impact (Heiniö et al., 2003). An extensive work about baked cereal products reviews bib- liographic data about aroma generation and summarises the possi- ble elaboration methods that can be used to control or modify flavour in this type of product (Pozo-Bayón, Guichard, & Cayot 2006a, 2006b). However, it has recently been pointed out that in addition to having a strong impact on organoleptic quality (i.e. col- our and flavour development) some thermally driven reactions can have an effect on nutritive value, produce antioxidative compo- nents and have toxicological implications. These findings explain why numerous research groups are today involved in research pro- jects aimed at gaining increased understanding of the reaction mechanisms occurring in food and determining ‘‘global” food qual- ity (Cost action 927; Martins, Jongen, & van Boekel, 2001; van Boe- kel, 2006). 0308-8146/$ - see front matter Ó 2008 Published by Elsevier Ltd. doi:10.1016/j.foodchem.2008.05.028 * Corresponding author. Fax: +33 (0) 169935020. E-mail address: Barbara.rega@agroparistech.fr (B. Rega). Food Chemistry 112 (2009) 9–17 Contents lists available at ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem