Journal of Cereal Science 45 (2007) 78–87 Reduction of (E)-2-nonenal and (E,E)-2,4-decadienal during sourdough fermentation Nicoline Vermeulen a , Michael Czerny b , Michael G. Ga¨nzle a,c , Peter Schieberle b , Rudi F. Vogel a,à a Technische Universita ¨t Mu ¨nchen, Technische Mikrobiologie, Weihenstephaner Steig 16, D-85350 Freising, Germany b Deutsche Forschungsanstalt fu ¨ r Lebensmittelchemie, Lichtenbergstrasse 4, D-85748 Garching, Germany c University of Alberta, Departement of Agricultural, Food and Nutritional Science, 4-10 Agriculture/Forestry Centre, Edmonton, Alta., Canada T6G 2P5 Received 10 April 2006; received in revised form 12 July 2006; accepted 16 July 2006 Abstract (E)-2-Nonenal and (E,E)-2,4-decadienal are key aroma compounds in wheat bread crumb. The fate of these unsaturated aldehydes in sourdoughs fermented with homo- and heterofermentative lactobacilli or baker’s yeast was investigated, and the metabolic pathways in these microorganisms identified. Clear differences were observed between homofermentative lactobacilli, heterofermentative lactobacilli and Saccharomyces cerevisiae. Heterofermentative strains rapidly reduced the concentrations of these aldehydes in dough, whereas S. cerevisiae displayed a lower activity. Lactobacillus sanfranciscensis reduced the aldehydes to the corresponding unsaturated alcohols, whereas S. cerevisiae reduced both the aldehyde moiety and the double bond, resulting in the formation of the corresponding saturated alcohols. S. cerevisiae first reduced the aldehyde moiety and then the double bond. In L. sanfranciscensis, the reduction of aldehydes is coupled to the oxidation of NADH to NAD + , which enables this heterofermentative strain to produce additional ATP from glucose. L. sakei, a strain that produces only lactic acid during sourdough fermentation, did not metabolise the unsaturated aldehydes at all. Both L. sakei and S. cerevisiae appeared to enhance aldehyde formation during the first hours of dough fermentation, probably due to the hydrogen peroxide production by these two strains. r 2006 Elsevier Ltd. All rights reserved. Keywords: Wheat sourdough fermentation; (E)-2-nonenal; (E,E)-2,4-decadienal; Lactobacilli; Baker’s yeast 1. Introduction A large and increasing amount of wheat bread and other baked products is produced using sourdough fermentation (De Vuyst and Neysens, 2005; Meuser and Valentin, 2004). The advantages of using sourdough and baking improvers based on sourdough are their beneficial effects on flavour (Hansen and Hansen, 1994a; Schieberle, 1996; Thiele et al., 2002), texture (Brandt et al., 2003), microbial shelf life (Lavermicocca et al., 2000) and delayed staling (Corsetti et al., 1998). The improved aroma of sourdough breads is caused by the microbial activity during fermentation and does not only rely on chemical acidification. Microbially fermented sourdoughs are reported to contain higher levels of volatile compounds than chemically acidified doughs (Hansen and Hansen, 1994a). Levels of volatiles in sourdough breads depend on the sourdough starter used (Czerny et al., 2005; Damiani et al., 1996; Hansen and Hansen, 1996; Hansen et al., 1989; Martinez-Anaya et al., 1990), and sensory panels use different attributes to describe sourdough bread made using different starters (Hansen and Hansen, 1996; Hansen et al., 1989). In traditional fermenta- tions, sourdough is used as the sole leavening agent. However, in most industrial applications, the combination of sourdough and baker’s yeast as leavening agent is applied. Depending on the fermentation conditions, the sourdough microflora is composed of yeasts and homofermentative as well as heterofermentative lactobacilli (Vogel et al., 1999). ARTICLE IN PRESS www.elsevier.com/locate/yjcrs 0733-5210/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jcs.2006.07.002 Abbreviations: cfu, colony-forming units; CI, chemical ionisation; EI, electron impact; HRGC/MS, high-resolution gas chromatography/mass spectrometry; MS, mass spectrometry; TD/HRGC/MS, two-dimensional high-resolution gas chromatography/mass spectrometry à Corresponding author. Tel.: +49 8161 7135169; fax: +49 8161 713327. E-mail address: rudi.vogel@wzw.tum.de (R.F. Vogel).