Proton-Transfer-Reaction Mass-Spectrometry (PTR-MS) for the study of the aromatic potential of bakery starter strains

The bio-preservation of perishable edible raw materials through fermentations represents the first biotechnological application and one of the first forms of food processing in human history. Flavor is one of the factors which mainly characterizes the degree of typicality of fermented products and influences consumers’ acceptability. Many Volatile Organic Compounds (VOCs) responsible for flavor (and off-flavor) perception are of microbial origin. Hence, microbial Volatile Organic Compounds (mVOCs), influencing the quality of food, affect consumer preference on fermented food, bread in our case. The huge number of geographical, compositional, microbiological and technological variables highlights the important need for tailored technologies to improve consumer acceptance of these traditional fermented foods. Direct-Injection Mass Spectrometric (DIMS) technologies, associating time resolution with high sensitivity and robustness, offer interesting insights in the field. Proton-Transfer-Reaction (PTR), combined to a Time-of-Flight (ToF) Mass Spectrometer (MS) is an analytical approach based on chemical ionization which belongs to the DIMS technologies. These techniques consented the rapid determination of VOCs in samples, assuring high sensitivity and accuracy. In general, PTR-MS doesn’t require neither sample preparation nor sample destruction, which allows real time and non-invasive analysis. PTR-MS features are exploited in many fields, from environmental and atmospheric chemistry to medical and biological sciences. In the last years, PTR-ToF-MS has been also applied in food science and technology, encompassing studies such as comparison of headspace versus nose-space VOC analysis, simulated in vivo conditions (e.g. simulating human mouth), VOC fingerprinting as a profiling methodology, VOCs associated with different producers, impact of different technological processes on VOC content, as well as the on-line monitoring of VOCs released during food processing. In this thesis, the recent upgrades we introduced on this technique, for the first time, are discussed and validated. In fact, in addition to the Switchable-eagent-Ion tested to study a simple Ethylene molecule, we developed an analytical methodology based on the coupling of PTR-ToF-MS with an autosampler and tailored data analysis tools, in order to increase the degree of automation and, consequently, to enhance the potential of this technique. This approach, permitted the screening of larger and more complex sample sets (i.e. fermenting dough), to analyze several experimental modes (e.g. different flour types, different yeast starters, different incubation hours), in order to monitor the bread-making bioprocess in terms of VOC content. In this work, the results of our approach on the simple chosen model are reported. Afterwards, this methodology is applied on a complex matrix which has never been studied before using this technique: dough, sourdough and baked bread (a traditional recipe adapted from Southern Italy). Hence, we report: i) the detection of VOCs released during alcoholic fermentation of the dough (on-line bioprocess monitoring), ii) the study of the interaction between different ingredients, iii) the monitoring of VOCs arising upon baking, iv) as well as the volatile profile of a sourdough model based on the realization of the complete volatomes of Saccharomyces cerevisiae and Lactobacillus sanfranciscensis. The general aim of this project is to conceive ‘tailored’ approaches to improve authenticity preservation and innovation management in the field of traditional fermented foods, a fascinating sector of the food industry relevant for the economy and for human nutrition. In addition, DIMS techniques, and especially PTR-MS, if considered high-throughput and rapid applications in ‘foodomics’ analysis, represent an intriguingly opportunity for the formulation of new hypotheses in food science and nutrition, particularly in the light of the recent attention attributed to fermented foods as valuable models of microbial ecosystems.