INVESTIGATING THE BIODIVERSITY IN SPONTANEOUS FERMENTATIONS AS A SOURCE OF HIGH-PERFORMANCE MICROORGANISMS

This PhD project was aimed at the investigation of spontaneously fermented food products with the goal of selecting highly performing strains to be used as starter cultures, in order to optimize the fermentation process and give to the final product an added value from a technologic, safety or sensory point of view. This project is divided in two parts dealing with two different fermentation processes. The first part is focused on sourdough fermentation and its potential to improve the baking performance of alternative grains such as spelt. Firstly, the dominating lactic acid bacteria (LAB) and yeasts were isolated and studied for their performance in fermentation as well as resistance to stress conditions. From the selected strains, one strain of Pediococcus pentosaceus was selected as a potential starter. To design a mixed starter culture, other LAB and yeast strains isolated from cereal fermentations were studied. First, we studied two LAB species, Weissella cibaria and W. confusa, that have interesting pro-technologic characteristics such as a good ability to produce exopolysaccharides, to degrade arabinoxylans and to inhibit the growth of some mold species. On the other hand, the two species have raised concerns as potential opportunistic pathogens. For this reason, combined genotypic and phenotypic studies were performed to assess the safety of the two species. Subsequently, an alternative non-Saccharomyces yeast species, Kazachstania unispora, was investigated as a leavening agent. The species had a good resistance to stress conditions and a good ability to ferment glucose, but lacked the ability to utilize maltose, the main carbon source in dough, for this reason it performed a slow leavening depending on the LAB to release free glucose. The selected strains were applied to a spelt-based sourdough bread with promising results; the LAB increased the mold-free shelf-life and improved the texture and conservation of the product, that received a high liking score in the sensory evaluation. The second part of the project regarded the cocoa fermentation and the possibility of using selected LAB as adjunct cultures to improve the quality of the chocolate in a controlled fermentation setup. Firstly, LAB and yeast strains were isolated and identified from natural cocoa fermentations. Two strains belonging to the species Lactiplantibacillus fabifermentans and Furfurilactibacillus rossiae were selected for further studies. We evaluated their adaptation to conditions associated with cocoa fermentations, such as low pH, high temperatures and high osmotic pressure as well as their ability to grow in conjunction with yeasts and acetic acid bacteria, whose activity is essential for cocoa fermentation. The two strains were then used as adjunct cultures in cocoa fermentations and the quality and sensory profile of the chocolate obtained was evaluated. This work allowed us to highlight the potential of autochthonous microbial strains with high level adaptation to the food matrix that allow not only to obtain a successful and reliable fermentation but to add to the safety, taste and quality of the final product.