On-line high-throughput analysis of the volatilome of microorganisms that have agroindustrial relevance

Yeast and bacterial species are widely used for leavening, brewing, wine making or dairy fermentations and play a key role in producing the characteristic sensory profile and perceived quality of these products through the volatile organic compounds (VOCs) they generate. These VOCs synthetized by microorganisms as secondary metabolites, not only impart important sensory notes but also have important technological functions. As such, an on-line and non-invasive screening of the microorganism volatilome is of high importance to better understand and control these processes and support innovation in this traditional sector by unlocking the flavor generation process. This contribution describes our activities investigating the potential of using ProtonTransfer-Reaction Time-of-Flight Mass Spectrometry (PTR-ToF-MS) coupled with multipurpose head-space automated sampling (MHSA) to enable the efficient monitoring of agroindustry-relevant microbiological processes: dough leavening, lactic acid fermentation, brewing and wine making. This experimental setup also enabled the measurement of VOCs produced by yeast grown on solid medium. Automation of the analytical process as provided by MHSA guaranteed reproducibility over the whole microorganism life cycle, the accurate control of process parameters (temperature and sampling times). Analysis could be completed as frequently as every second but typically the headspace of each sample was measured for one minute while displacing the headspace with zero air or pure nitrogen. In addition, the fermentation processes can automatically be monitored for several hours in the case of dough leavening and lactic acid fermentations or days for alcoholic fermentations or yeast colonies grown on a solid medium. The set-up allows the monitoring of 128 samples at the same time. To deal with data matrices containing several hundred of mass peaks for each measurement multivariate data analysis is needed to provide the general overview of biological processes and phenotypic variability among different microbial strains. Observations of single VOC emission curves allow the opportunity to study known metabolic pathways and unravel unknown ones. In general, PTR-ToF-MS coupled to MHSA allows insight into the dynamic nature of the microorganism volatilome and, consequently, on flavor.