Esopolisaccaridi di origine microbica come postbiotici per lo sviluppo di nuovi alimenti funzionali

Exopolysaccharides of microbial origin provide, thanks to their technological and functional properties, an extraordinary opportunity for the development of new food products with high added value. Although microbial EPS are known to enhance the sensory and health-related char-acteristics of foods, it is still a field that requires further scientific analysis, especially in relation to the need to increase yields and clarify some aspects related to their interactions with the gut microbiota. Thus, the primary goal of this Ph.D. project was to isolate and characterize novel microbial EPS produced by LAB with desirable bioactivities for the development of new func-tional food products. First, LAB were isolated from fermented foods and screened for EPS production to identify the highest performers. Through a qualitative and quantitative approach, twelve strains of LAB, in-cluding Lb. plantarum, Lb. paracasei, Lc. lactis, and Leuc. mesenteroides, were identified, which could produce more than one gram of EPS per liter. Some of these strains were selected for further re-search (Chapter 2). In an effort to improve EPS yields, the impact of both traditional and non-traditional strategies was examined. It was found that an initial pH of 8, which is significantly higher than the opti-mal, can greatly stimulate EPS biosynthesis in most strains. The use of pretreatments with MIPEF has been also identified as a highly promising strategy, resulting in a production increase of EPS by at least eight times (Chapter 3). The results of these first steps have shone the spotlight on three strains, whose EPS were sub-jected to an in-depth chemical, morphological, and functional characterization. An EPS produced by Leuc. mesenteroides B3, isolated from an Italian semi-hard cheese, was iden-tified as a mixture of two dextrans having different Mw. This EPS showed to have potential as an antimicrobial and antibiofilm agent, especially against L. monocytogenes. It also stimulated bifidobacteria, potentially making them more robust during food processing and storage (Chap-ter 4). EPS from Leuc. mesenteroides F02A5, isolated from raw milk cheese, is a high-Mw dextran with a linear structure. EPS displayed antimicrobial activity against some foodborne pathogens, as well as radical scavenging capacity. Moreover, the polymer was characterized by high solubility and capacity to retain water, which could be very useful in specific food formulations (Chapter 5). Leuc. mesenteroides PM01A5 strain, isolated from sourdough, produced an EPS made of a mixture of dextran and levan. This polymer exhibited antimicrobial activity and particularly stood out for its strong antioxidant potential (Chapter 6). At the end of this path of exploration of the potential of microbial EPS, in collaboration with the research group supervised by Prof. Paul Cotter, from the Food Bioscience Dept. of Teagasc Food Research Centre, Cork, Ireland, two of the most promising EPS were used to enrich a soymilk fermented beverage. One of them was shown to drastically increase the alpha diversity of the gut microbial community during an ex vivo faecal fermentation, also stimulating the prolif-eration of the beneficial bacterial species Bif. adolescentis, Bif. longum, Anaerostipes hardus, and Fae-calibacterium praustnizii, therefore offering exciting prospects for potential functional uses (Chapter 7).

Exopolysaccharides of microbial origin provide, thanks to their technological and functional properties, an extraordinary opportunity for the development of new food products with high added value. Although microbial EPS are known to enhance the sensory and health-related characteristics of foods, it is still a field that requires further scientific analysis, especially in relation to the need to increase yields and clarify some aspects related to their interactions with the gut microbiota. Thus, the primary goal of this Ph.D. project was to isolate and characterize novel microbial EPS produced by LAB with desirable bioactivities for the development of new functional food products. First, LAB were isolated from fermented foods and screened for EPS production to identify the highest performers (Chapter 2). Through a qualitative and quantitative approach, twelve strains of LAB, including Lb. plantarum, Lb. paracasei, Lc. lactis, and Leuc. mesenteroides, were identified, which could produce more than one gram of EPS per liter. The initial step of the research has revealed three Leuconostoc strains that produced the highest yields. These strains have been used as the basis of Chapter 3, Chapter 4, and Chapter 5, where the EPS were analyzed in-depth with regards to their chemical, morphological, and functional properties. An EPS produced by Leuc. mesenteroides B3, isolated from an Italian semi-hard cheese, was identified as a mixture of two dextrans having different Mw. This EPS was shown to have potential as an antimicrobial and antibiofilm agent, especially against L. monocytogenes. It also stimulated bifidobacteria, potentially making them more robust during food processing and storage (Chapter 3). This EPS from Leuc. mesenteroides F02A5, isolated from raw milk cheese, is a high-Mw dextran with a linear structure. EPS displayed antimicrobial activity against some foodborne pathogens, as well as radical scavenging capacity. Moreover, the polymer was characterized by high solubility and capacity to retain water, which could be very useful in specific food formulations (Chapter 4). Leuc. mesenteroides PM01A5 strain, isolated from sourdough, produced an EPS made of a mixture of dextran and levan. This polymer exhibited antimicrobial activity and particularly stood out for its strong antioxidant potential (Chapter 5). At the end of the exploration of the potential of microbial EPS, in collaboration with the research group supervised by Prof. Paul Cotter, from the Food Bioscience Dept. of Teagasc Food Research Centre, Cork, Ireland, two of the most promising EPS were used to enrich a fermented soy beverage. One of them was shown to drastically increase the alpha diversity of the gut microbial community during an ex vivo faecal fermentation, also stimulating the proliferation of the beneficial bacterial species Bif. adolescentis, Bif. longum, A. hardus, and F. praustnizii, therefore offering exciting prospects for potential functional uses (Chapter 6). Finally, in an effort to improve EPS yields, the impact of both traditional and non-traditional strategies was examined. It was found that an initial pH of 8, which is significantly higher than the optimal, can greatly stimulate EPS biosynthesis in most strains. The use of pretreatments with MIPEF was also identified as a highly promising strategy, resulting in a production increase of EPS by at least eight times (Chapter 7).