Real-Time monitoring of flavoring starter cultures for different food matrices using PTR-MS

In fermented foods, volatile organic compounds (VOCs), which are often metabolic products of microorganisms, form a subset of the chemical compounds contributing to the sensory perceptions arising during product consumption. Direct injection mass spectrometry (DIMS) techniques allow for the direct and real-time measurement of VOC release without the need for laborious sample treatment, extraction procedures, and chromatographic separation. DIMS has been successfully applied in different fields, including characterizing the formation of flavor compounds associated with fermentation bioprocesses in foods and beverages. In this chapter, following a general overview on DIMS for the study of fermentation generated VOCs, the use of proton transfer reaction time-of-flight mass spectrometry (PTR-TOF-MS to investigate VOC generation during the fermentation bioprocesses in yeast-based fermentations and to characterize the flavor contributions of starter cultures is described. To this extent, a panel of five experiments is presented that demonstrates a pipeline of increasing complexity where DIMS is used to monitor VOC release in association with a) yeasts grown in a standard culture media, b) the growth of different yeast starter cultures in a real food matrix, c) the interaction between yeast starter cultures and different wheat flours, d) the interaction between different combinations of starter cultures grown in multiple food matrices, and e) the contribution of commercial starter cultures to specific flavor attributes in a food matrix. Fermentation is globally recognized as one of the key sustainable technologies in food science, and DIMS offers a low-cost, time-saving, and low-impact methodology to investigate fundamental themes and support agroindustry applications. Hence, the proposed approach is of interest to the fields of food biotechnology and flavor science but, this coupling of ‘green’ biotechnological and analytical solutions also represents a bridge towards improved sustainability of agro-food systems.