Hanna El-Nakat

Proton-transfer-reaction mass spectrometry for the study of the production of volatile compounds by bakery yeast starters

The aromatic impact of bakery yeast starters is currently receiving considerable attention. The flavor characteristics of the dough and the finished products are usually evaluated by gas chromatography and sensory analysis. The limit of both techniques resides in their low-throughput character. In the present work, proton-transfer-reaction mass spectrometry (PTR-MS), coupled to a time-of-flight mass analyzer, was employed, for the first time, to measure the volatile fractions of dough and bread, and to monitor Saccharomyces cerevisiae volatile production in a fermented food matrix. Leavening was performed on small-scale (1 g) dough samples inoculated with different commercial yeast strains. The leavened doughs were then baked, and volatile profiles were determined during leavening and after baking. The experimental setup included a multifunctional autosampler, which permitted the follow-up of the leavening process on a small scale with a typical throughput of 500 distinct data points in 16 h. The system allowed to pinpoint differences between starter yeast strains in terms of volatile emission kinetics, with repercussions on the final product (i.e. the corresponding micro-loaves). This work demonstrates the applicability of PTR-MS for the study of volatile organic compound production during bread-making, for the automated and online real-time monitoring of the leavening process, and for the characterization and selection of bakery yeast starters in view of their production of volatile compounds.

Volatile Compound Production During the Bread-Making Process: Effect of Flour, Yeast and Their Interaction

Bread is one of the most consumed products around the world, justifying the continuous research and development activities on how to improve its sensory, chemical and industrial characteristics. Volatile organic compounds (VOCs) play a key role in this regard because they take shape during the leavening process and are enhanced upon baking. In this study, proton-transfer reaction mass spectrometry (PTR-MS), coupled to a time-of-flight (ToF) mass analyser, was undertaken in order to analyse the effects of Saccharomyces cerevisiae strains as well as the type of wheat flour used in the bread-making process on VOC production. The results showed a greater impact of yeast strains over the expected flour influence. This observation was confirmed when the leavened dough samples were baked and the volatile profiles determined. However, the peak-by-peak monitoring, followed by a tailored statistical approach, revealed not only the effect of changing ingredients but also different kinds of yeast/flour interaction. Such findings shed a new light on the selection of ingredients for each bread recipe depending on the desired volatile profile of the baked product and on the potential of PTR-MS in analysing protechnological microbes/matrix interaction during food fermentations.