Sourdough fermentation processes: meta-analysis, impact of pH evolution, and online real-time monitoring by selected ion flow tube-mass spectrometry

Promovendus/a: Simon Van Kerrebroeck

Promotor(en): Prof. Dr. ir. Luc De Vuyst

Food fermentations are dynamic processes, which are generally monitored offline. Although online analysis of physicochemical parameters such as temperature and pH has become routine and online measurement of exhaust gases is possible, dynamic studies for the monitoring of process parameters and fermentation properties, in particular the production of volatile compounds, are lacking. This is particularly important for the follow-up of sourdough fermentation processes, which are started with non-sterile flour and other ingredients, are subject to contamination from the environment, in particular if performed spontaneously or through backslopping, are fermented by communities of lactic acid bacteria (LAB) and yeasts under different process conditions, and are destined for the production of baked goods. The latter are often evaluated, both by consumers and producers, as to their aroma and flavour, whether or not by objective means.

The present study contributed to the development of methodologies to monitor sourdough fermentation processes online and in real-time, in parallel with off-gas analysis, based on selected ion flow tube-mass spectrometry (SIFT-MS). This is an easy-to-use and promising technique in the field of food and flavour analysis. In a first instance, ethanol as major volatile sample compound was detected with an optimized protocol. However, its high fermentor headspace concentrations influenced the measurements of other volatile sample compounds that are characteristic for the sourdough aroma profile. Therefore, an adapted workflow for the analysis of the SIFT-MS data was developed subsequently, which enabled the monitoring of the volatile sample compounds acetoin and ethyl acetate, together with ethanol, during the production of liquid wheat sourdoughs obtained by fermentation with several potentially interesting hetero- and homofermentative volatileproducing LAB starter culture strains and an acetic acid bacterial starter culture strain. Finally, SIFT-MS allowed to distinguish sourdoughs and breads from different origins.